bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and folded conformation of some 5,15‐diaryloctamethylporphyrins with a sulfonyloxy group in the aryl part
Authors: Sanders G. M. , van Dijk M. , Koning G. P. , van Veldhuizen A. , van der Plae H. C.
Published: September 2010

The porphyrins 1a‐g were synthesized. In CDCl3 solution 1a and 1b occur to an important extent in a folded conformation, as is indicated by an upfield shift of 2‐3 ppm for the tosylprotons in the 1H NMR spectrum. For compounds with longer chains or an ester instead of a sulfonyloxy group the upfield shift is much smaller.
Reduction of unsaturated β‐oxo esters: Synthesis of unsaturated β‐hydroxy esters and of unsaturated 1,3‐diols
Authors: van den Goorbergh J. A. M. , Nonneman L. E. Y. , van der Gen A.
Published: September 2010

The β‐carbonyl group of the unsaturated β‐oxo esters 1 and 2 can be selectively reduced using sodium tetrahydroborate in methanol to give the γ‐ and δ‐unsaturated β‐hydroxy esters 3 and 4, respectively. The unsaturated 1,3‐diols 5 and 6 were obtained by reduction of the β‐carbonyl group as well as the ester function of unsaturated β‐oxo esters 1 and 2 using lithium tetrahydroaluminate. For the conversion of γ‐unsaturated β‐oxo esters 1, with R1 = H and R2 = aryl, into the corresponding unsaturated diols 5, hydrobis(2‐methylpropyl)aluminum was used to prevent reduction of the double bond.
Synthesis of 5‐, 6‐, 7‐ and 18‐mono‐13C‐labelled retinals
Authors: Courtin J. M. L. , Lam G. K.'T , Peters A. J. M. , Lugtenburg J.
Published: September 2010

Four retinals labelled at positions 5, 6, 7 and 18 with 13C were obtained via simple schemes involving only a few steps with > 98% chemical purity and 92% 13C incorporation. (5‐13C)Retinal was obtained in 26% yield from K13CN. (6‐13C)‐ and (7‐13C)Retinal were obtained in 37% yield from (2‐13C)‐ and (1‐13C)acetonitrile, respectively, while (18‐13C)retinal was obtained in 8 steps and 4% yield starting from 13CH3I. Their 13C‐ 1H and 13C‐ 13C NMR coupling constants were determined.
A novel water‐soluble fluorescent probe: Synthesis, luminescence and biological properties of the sodium salt of the 4‐sulfonato‐3,3′,5,5′‐tetramethyl‐2,2′‐pyrromethen‐1,1′‐BF2 complex
Authors: Wories H. J. , Koek J. H. , Lodder G. , Lugtenburg J. , Fokkens R. , Driessen O. , Mohn G. R.
Published: September 2010

The reaction of the 3,3′,5,5′‐tetramethyl‐2,2′‐pyrromethen‐1,1′‐BF2 complex with chlorosulfonic acid and its subsequent neutralisation with sodium bicarbonate yields the titled compound 1, which, in addition to appropriate thermal and photochemical stability, possesses excellent fluorescent properties. As a preliminary assay of its potential usefulness as a fluorescent probe in medical and biological research, the chemical was administered intravenously to rats and possible signs of toxicity were recorded. The rats showed no apparent detrimental effects and excreted the compound in the urine within three hours. In tests in which Salmonella and E. coli strains were used as indicators of genotoxicity, no mutagenic effects were observed.
Reductive introduction and oxidative removal of the 4‐methoxybenzyl ether in the presence of the azido group. Synthesis of 2‐azido‐2‐deoxy sugars having chain extension at C‐4
Authors: Kloosterman M. , Kuyl‐Yeheskiely E. , van Boom J. H.
Published: September 2010

3,4,6‐Tri‐O‐acetyl‐2‐azido‐2‐deoxy‐α‐D‐glucopyranosyl bromide was converted in four steps into allyl 2‐azido‐3‐O‐benzoyl‐2‐deoxy‐4,6‐O‐(4‐methoxybenzylidene)‐β‐D‐glucopyranoside. Treatment of the latter with sodium cyanoborohydride and hydrogen chloride in oxolane (THF) gave allyl 2‐azido‐3‐O‐benzoyl‐2‐deoxy‐6‐O‐(4‐methoxybenzyl)‐(β‐D‐glucopyranoside. Further, 3,4,6‐tri‐O‐acetyl‐2‐azido‐2‐deoxy‐α‐D‐galactopyranosyl bromide was converted in five steps into allyl 2‐azido‐3‐O‐benzoyl‐2‐deoxy‐6‐O‐(4‐methoxybenzyl)‐β‐D galactopyranoside. The 4‐methoxybenzyl ether could be removed in the presence of the azido function using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ).
The preparation of 1‐aminopurinium mesitylenesulfonates by reaction of purines with O‐(mesitylenesulfonyl)hydroxylamine
Authors: Kos N. J. , Jongejan H. , van der Plas H. C. , van Veldhuizen A.
Published: September 2010

A number of 1‐aminopurinium mesitylenesulfonates have been prepared in reasonable to good yields by treatment of the corresponding purines with O‐(mesitylenesulfonyl)hydroxylamine. The structure of these salts has been established by means of 1H and 13C NMR spectroscopy, using, as diagnostic tools, the J(H‐2, H‐6), 3J(C‐2, H‐6) and 3J(C‐6, H‐2) coupling constants for compounds which are unsubstituted at positions 2 and 6 and the 13C Δδ values of C‐2 or C‐6 and C‐8 for C‐2 or C‐6 substituted purinium salts.
The chemistry of small‐ring compounds. Part 49. A route to oxaspiropentanes, undisturbed by rearrangement
Authors: Hofland A. , Steinberg H. , de Boer Th. J.
Published: September 2010

The title compounds have been prepared in 70‐90% yield by epoxidation of appropriate cyclopropylidene compounds with KHSO5 in a phosphate buffer in the presence of acetone. The latter is converted into an unstable dioxirane, which acts as the oxygen‐transferring agent.
Synthesis of some modified 2′‐5′‐linked oligoriboadenylates of 2‐5A core
Authors: Visser G. M. , Tromp M. , van Westrenen J. , Schipperus O. , van Boom J. H.
Published: September 2010

The synthesis of three analogues of 2′‐5′‐linked oligoriboadenylates is reported. Two trimers, having at the 2′‐end a 3′‐amino‐ (or 3′‐tetradecanamido)‐3′‐deoxy‐riboadenosine, were assembled via a phosphotriester approach. In the same way, we also prepared a tetramer carrying at the 2′‐end β‐L‐riboadenosine instead of β‐D‐riboadenosine. The non‐terminal building unit 3′,5′‐O‐(tetraisopropyldisiloxane‐1,3‐diyl)‐N6‐benzoyladenosine and the appropriately protected modified riboadenosines were coupled using the phosphorylating agent 2‐chlorophenyl‐O,O‐bis(1‐benzotriazolyl) phosphate. The removal of all protecting groups from the intermediate trimers and tetramer was effected by ammonolysis, followed by treatment with fluoride ions.
Synthesis of retinals isotopically labelled at positions 11, 12, 14 and 20
Authors: Pardoen J. A. , van den Berg E. M. M. , Winkel C. , Lugtenburg J.
Published: September 2010

Five retinals, having different combinations of 2H, with one having 2H and 13C labels at positions 11, 12, 14 and 20, were obtained with a chemical purity of above 98%, a level of 2H enrichment greater than 95% and with 13C enrichment of 99%. The retinals concerned are (20,20,20‐2H3)‐, (12,20,20,20‐2H4)‐, (12,14,20,20,20‐2H5)‐, (11,14‐2H2)‐, (12,14‐2H2)‐ and (12,14‐2H2,20‐13C)retinal.
Chemistry of four‐membered cyclic nitrones. Reaction with a non‐nucleophilic base: Stereoselective ring opening of in situ generated 1,2‐dihydroazetes and structure elucidation of the resulting α,β‐unsaturated oximes by X‐ray analysis
Authors: van Eijk Peter J. S. S. , Reinhoudt David N. , Harkema Sybolt , Visser Richard
Published: September 2010

The four‐membered cyclic nitrones (2,3‐dihydroazete 1‐oxides) 1a‐g isomerize to the corresponding oximes 3 and 4 on treatment with potassium tert‐butoxide. In N,N‐dimethylformamide at room temperature, oxime 4 is formed preferentially; in tetrahydrofuran, both the oximes 3 and 4 are formed. The oximes 3c‐e are converted into the corresponding 6H‐1,2‐oxazin‐6‐ones 5c‐e by reaction in acetic acid. The oxime 4a has the (E,E) stereochemistry and the O‐benzoyl derivative of 3b (6) the (Z,E) stereochemistry, as shown by X‐ray analysis. In solution, NOE difference spectroscopy indicates the (Z,E) and (E,E) configuration for 3a and 4a, respectively. The α,β‐unsaturated ketone (Z)‐8 was prepared by reaction of (Z,E)‐3b with bispyridine silver permanganate. Reaction of (Z)‐8 with hydroxylamine in pyridine yields (Z,E)‐3b and the 6H‐1,2‐oxazin‐6‐one 5b, which is formed by rapid cyclization of (Z,Z)‐3b.

The conversion of nitrones 1 into the corresponding oximes 3 and 4 is explained in terms of an electrocyclic ring opening of an intermediate N‐hydroxy‐1,2‐dihydroazete. In this electrocyclic reaction, a strong preference for outward rotation of the hydroxy group is observed.
Energy migration in rare‐earth compounds
Authors: Blasse G.
Published: September 2010

The luminescence processes in several rare‐earth compounds are discussed, viz. sensitization, one‐step energy transfer, multi‐step energy transfer (migration) and trapping. Results are given for compounds containing Eu3 +, Tb3+ and Gd3+. The dimensionality of the rare‐earth sublattice (three, two or one) influences the migration and examples are presented. The case of Eu3+ is the first for which one‐, two‐ and three‐dimensional migration has been observed for one and the same optically active ion. Gadolinium compounds can be applied in luminescent lamps, where they improve the lamp output considerably.
Configuration‐dependent conformational transmission in trigonal‐bipyramidal Pv compounds. Enhanced gauche (‐) population around the C(5)‐C(6) linkage in 6‐Pv phosphorylated tetramethyl‐α‐D‐galactopyranoside
Authors: de Vries N. K. , Buck H. M.
Published: September 2010

A 300‐MHz 1H NMR variable‐temperature study of the 1′‐phosphorylated trigonal‐bipyramidal (TBP) tetrahydropyran‐2‐methyl model compound 4 is reported. For this compound, in which both the equatorial and axial sites undergoing phosphorus pseudorotation bear a tetrahydro‐pyran‐2‐methyl group, a precise conformational analysis of the C(1′)‐C(2) bond is possible. The thermodynamic parameters which result from this analysis allow the assignment of the proton resonating at low field as H(1′). It is shown that, for the group situated axially in the Pv TBP, an enhanced gauche (‐) population [O(1′) and O(1) trans‐situated] occurs around C(1′)‐C(2) (290 K, 59%; 230 K, 74%) as compared to the corresponding Piv compound 3 (298 K, 10%). The same conformational transmission is observed for 6‐phosphorylated pyranosides, but in this case is found to depend upon the configuration at C(4). It appears that 6‐phosphorylated methyl 2,3,4‐tri‐O‐methyl‐α‐D‐galactopyranoside shows a conformational change around C(5)‐C(6) towards a higher g− population, going from 6‐Piv to 6‐Pv TBP, which is absent in the corresponding 6‐phosphorylated methyl 2,3,4‐tri‐O‐methyl‐α‐D‐glucopyranoside. Apparently, the configuration at C(4) is jointly liable for the transmission in the Pv TBP.
Photochemistry of α‐oxo oximes. Part 9. The γ‐hydrogen abstraction in α‐oxo oxime ethers
Authors: Buys Theo S. V. , Cerfontain Hans , Geenevasen Jan A. J. , Stunnenberg Frank
Published: September 2010

The photochemistry (λ 300 nm) of the α‐oxo oxime ethers 1a and 2a has been studied with the objective of detecting any γ‐H abstraction. Direct irradiation of (Z)‐1a results only in (E)‐(Z) isomerization, whereas direct irradiation of the isomeric α‐oxo oxime ether 1b and the corresponding α‐diketone 1c leads mainly to cyclobutanol formation. The absence of cyclobutanol formation with 1a is ascribed to the higher angle of twist of the intercarbonyl‐iminyl angle of the reacting excited state of 1a, as compared with those of both 1b and 1c.

The photodeuteration of the 7‐methyl hydrogens of 2a, using C2H3O2H as (co)‐solvent, is a very inefficient process (Φ 7.0 × 10−5), and that of the benzylic hydrogens of the related ketone 3a is even more inefficient (Φ ≤ 0.5 × 10−5). The inefficiency is ascribed mainly to the relatively low rate of γ‐H abstraction in the excited triplet (nπ*) state as well as to the very short life‐times of the ground state (Z)‐enols resulting from the relatively high rate of reketonization. The higher photodeuteration yield of the α‐oxo oxime ether 2a, as compared with the benzylic hydrogens of 3a, is ascribed to stabilization of the triplet 1,4‐diradical formed by γ‐hydrogen abstraction of the excited triplet (Z)‐2a, which results from electron delocalization and intramolecular hydrogen bonding.
NAD(P)H models XXII. Magnesium ion mediated acid catalysis of the reduction of imines by Hantzsch ester
Authors: van Niel J. C. G. , Kort C. W. F. , Pandit U. K.
Published: September 2010

Reduction of imines (2a‐e) derived from n‐butylamine and p‐substituted benzaldehydes, in the presence of magnesium perchlorate, by Hantzsch ester (1), in acetonitrile, proceeds via the corresponding iminium salts formed by protonation of the imines by [Mg(H2O)L5]2+ complexes. These complexes are produced by reaction of Mg2+ ions with water, which is associated with the solvent acetonitrile. Within the range 1.67 × 10−3‐26.11 × 10−3 M of added water, the rate of the reaction shows a direct dependence upon the concentration of water. Rates of reduction of the iminium perchlorates of 2a‐e exhibit a Hammett relationship with a ρ value of + 1.83.
Sulfur trioxide sulfodeprotonation of the rigidly bridged 1,6:8,13‐propane‐1,3‐diylidene[14]annulene
Authors: de Wit Peter , Kruk Cor , Cerfontain Hans
Published: September 2010

The sulfodeprotonation of 1,6:8,13‐propane‐1,3‐diylidene[14]annulene (1) with sulfur trioxide in dioxane and nitromethane at 20°C has been studied. Reaction of1with SO3in (2H8)dioxane yields initially only the 2‐sulfonic acid which is subsequently converted into about equal amounts of the 2,9‐ and 2,12‐disulfonic acid. Upon using 6.0 and 8.0 equiv. of SO3in (2H8)dioxane, the very rapid formation of the 2,9‐ and 2,12‐disulfonic acids is followed by a relatively slow conversion into a mixture of the 2,4,9‐, 2,4,12‐ and 2,5,9‐trisulfonic acids in a ratio ofca.3/3/2. Reaction of1with 8.5 equiv. of SO3in (2H3)nitromethane gave the 2,4,9,11‐, 2,4,9,12‐, 2,4,10,12‐ and 2,5,9,12‐tetrasulfonic acid in yields of 20, 39, 35 and 6%, respectively. The observed sulfonic acid isomer distributions are discussed in terms of the directing effects of the “ideal” [14]annulene and the sulfo substituent(s) already present.
The benzylic effect in nucleophilic attack on oxiranes
Authors: Lynas‐Gray Jack I. , Stirling Charles J. M.
Published: September 2010

Reactivities of 2‐phenyloxirane (4) and trans‐2,3‐diphenyloxirane (6) towards nucleophiles are comparable with those of non‐benzylic oxiranes; in aryloxiranes for which an antiperpendicular trajectory of the nucleophile orthogonal to the plane of the aryl ring is required, considerable increases in reactivity over non‐benzylic models are found.
13C NMR studies of p‐substituted nitrosobenzenes
Authors: Al‐Tahou Baheeja M. , Gowenlock Brian G.
Published: September 2010

The 13C NMR spectra of a wide range of monomeric para‐substituted nitrosobenzenes have been determined and the results related to a wide range of published data for other para‐disubstituted benzenes. It is shown that the nitroso substituent exercises a different pattern of effect for the 13C chemical shifts at the ipso C atom from at least twenty eight other substituents. It is noted that when the para substituent is a π‐donor, the nitroso group functions in a different manner from that operative when the para substituent is a π‐acceptor, a general possibility that has already been suggested in the recent literature.
Synthesis and spectroscopic study of 1,1′‐methylene‐2,2′‐pyrromethen‐5[1H]‐one and its 3,4‐dihydro and 2,3,4,6‐tetrahydro derivative
Authors: van Es J. J. G. S. , Koek J. H. , Erkelens C. , Lugtenburg J.
Published: September 2010

The Z‐syn‐locked 1,1′‐methylene‐2,2′‐pyrromethen‐5(1H]‐one 1, prepared in 45% yield in a one‐pot reaction from the previously reported 1,1′‐methylenebis(pyrrole‐5‐carbaldehyde) (8), exhibits a brilliant fluorescence with a high quantum yield (1.0) in contrast to the parent 2,2′‐pyrromethen‐5[1H]‐one systems. The λmax of emission and the quantum yield are solvent dependent. Catalytic reduction of 1 affords the 3,4‐dihydro derivative 2 in 80% and the 2,3,4,6‐tetrahydro derivative 3 in 80% and 95% yields, respectively. Compounds 2 and 3 exhibit no fluorescence, however 2 shows a very efficient photoFries‐type rearrangement. Advanced 1H NMR techniques had to be applied in order to obtain the complete analysis of the 1H NMR spectrum of 3, which showed the conformational details of its reduced bicyclic moiety.
Photochemistry of 3‐methyl‐1,2‐dihydronaphthalene
Authors: Laarhoven W. H. , Berendsen N.
Published: September 2010

Irradiation of the title compound (6) with a broad spectrum lamp at room temperature afforded 2‐methylidene‐1,2,3,4‐tetrahydronaphthalene (8) and 2‐methylnaphthalene (7). Apart from 8, irradiation of 6 at −45°C also afforded 5‐methylbenzobicyclo[3.1.0]hex‐2‐ene (12) 1‐methylidene‐2‐(2‐tolyl)cyclopropane (13) as well as a small amount of 2‐methyl‐1,4‐dihydronaphthalene (14). Both 12 and 13 originate from the ring‐opened product of 6. Compound 14 is probably formed via a retro di‐π‐methane rearrangement from 12.

Irradiation of 6 in n‐propylamine afforded the same photoproducts, 14 being the main one in this case.
The bonding of H2 in W(CO)5(H2), a reactive intermediate stabilized and identified in liquid xenon
Authors: Andréa Ronald R. , Vuurman Michael A. , Stufkens Derk J. , Oskam Ad
Published: September 2010

Liquid Xenon (LXe) appears to be an ideal solvent for the study of reactive intermediates in photochemical reactions because of its complete inertness and transparency in both the IR and UV/Visible spectral regions. Photolysis of a H2‐doped solution of W(CO)6 in LXe at 193 K leads to the formation of W(CO)5H2 having CO stretching modes at 2098.4 (A21), 1972.2 (E) and 1970.5 cm−1 (A11) and v(H‐H) at 2707 cm−1. From a comparison of these CO stretching frequencies with those of other W(CO)5L complexes it is concluded that the W(dπ) → H2(σ*u) interaction is stronger than expected theoretically.
The meta photocycloaddition of fluoroarenes to cyclopentene
Authors: Osselton E. M. , Krijnen E. S. , Lempers E. L. M. , Cornelisse J.
Published: September 2010

The meta photocycloaddition of fluorobenzene and disubstituted fluoroarenes to cyclopentene has been investigated. From the effects of the various substituents and the varying product ratios it can be concluded that the reaction must proceed via a polar mechanism.
Photochemical reactions of 1‐acetyl‐3‐methylbicyclo[1.1.0]butane
Authors: Cerfontain Hans , Geenevasen Jan A. J.
Published: September 2010

The photochemistry of 1‐acetyl‐3‐methylbicyclo[1.1.0]butane in various solvents usingλ 254 and 300 nm radiation has been studied. In inert solvents, photoisomerization occurs with formation of 3 and 4 with subsequent photoconversion of 3 into 5. The (3 + 5)/4 ratios are significantly greater forλ 254 than forλ 300 nm radiation, illustrating direct reaction from the π* excited state(s). Additional photoreduction to 6 was observed forλ 300 nm in hydrogen‐donating solvents, especially in diisopropyl ether and toluene. In carbon tetrachloride, atλ 300 nm, mainly the HCl addition compound 10 is formed via ketone‐photosensitized decomposition of CCl4. Similarly, with methanol, 2‐propanol and water as solvent or addendum, the 1,3‐addition products 7–9 are obtained. Under all of these conditions, no photoproducts containing the intact bicyclo[1.1.0]butyl group were found, illustrating the high chemical reactivity of this severely strained group.

Mechanisms for the formation of the photoisomerization, photoreduction and 1,3‐dipolar addition products are proposed.
Effect of pressure on the (2 + 2) cycloaddition of ethoxycyclopropane to tetracyanoethylene
Authors: Wiering Petrus G. , Steinberg Herbert
Published: September 2010

The pressure dependence of the (2 + 2) cycloaddition of ethoxycyclopropane 1 to tetracyanoethylene in various solvents has been studied.

Only 3‐ethoxy‐1,1,2,2‐cyclopentanetetracarbonitrile 2 is formed in p‐dioxane and acetonitrile. The reaction in benzene, however, also gives rise to the ring‐opened enol ether 4E/Z, which rapidly reacts further with TCNE. The volume of activation is found to be −29.2 cm3/mole (CH3CN) and − 33.7 cm3/mole (p‐dioxane). These findings point to a two‐step cycloaddition mechanism involving a dipolar transition state.
The use of sulfenyl halides in the synthesis of mercapturic acids and their esters
Authors: Buijs Wim , van der Gen Arne , Eid Mohammed I. A. , Onkenhout Willem , Vermeulen Nico P. E.
Published: September 2010

A new method for the synthesis of mercapturic acids (N‐acetyl‐S‐substituted‐L‐cysteines), based on the addition of sulfenyl halides to olefins, is described. Alkenes and alkynes of widely different structure have been converted in this way into fully characterized mercapturic acids and their methyl esters.
Synthesis and reactions of 3‐alkoxy‐2H‐azirines
Authors: Ghosez L. , Sainte F. , Rivera M. , Bernard‐Henriet C. , Gouverneur V.
Published: September 2010

3‐Alkoxy‐2H‐azirines 4 have been prepared by treatment of enol ethers 6 with iodine azide followed by base‐catalysed elimination of HI and thermolysis of the resulting vinyl azide 5. Azirines 4 readily undergo electrophilic additions, to yield products resulting from cleavage of either the N(1)‐C(3) or the N(1)‐C(2) bond. Reaction of 4 with trimethylsilyl cyanide yields highly functionalized aziridines 12. Thermolysis of 4 produces C‐alkoxy‐N‐vinylmethanimines.
Synthesis of 5‐deazaflavin adenine dinucleotide (5‐dFAD) using a modified triester approach
Authors: Smit P. , Stork G. A. , van der Plas H. C. , den Hartog J. A. J. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Starting from D‐ribose and 3,4‐xylidine, a fifteen‐step synthesis is described for the preparation of 5‐dFAD (18). The synthesis involves as key intermediates, 5‐deazariboflavin (8), its 2′,3′,4′‐tris‐O‐(tetrahydropyranyl) derivative (12) and 2′,3′,4′‐tris‐O‐(tetrahydropyranyl)‐5′‐O‐(morpholinophosphonyl)‐5‐deazariboflavin (15).
4,5α‐epoxy‐3‐methoxy‐8β‐nitro‐6β, 14β‐ethenomorphinan, a novel type Diels‐Alder adduct from 6‐demethoxy‐17‐formylnorthebaine and nitroethene (Chemistry of opium alkaloids, part XXIII)
Authors: Prazeres M. A. , Peters J. A. , Linders J. T. M. , Maat L.
Published: September 2010

4,5α‐Epoxy‐3‐methoxy‐8β‐nitro‐6β, 14β‐ethenomorphinan (5) was isolated as one of two major cycloaddition products of 6‐demethoxy‐17‐formylnorthebaine (3) and nitroethene. Structure elucidation was mainly based on 1H NMR data.
Crystal and Molecular Structure of 1,2‐Diphenylcyclopentene, C17H16. A redetermination
Authors: Smits J. M. M. , Beurskens Paul T. , Laarhoven W. H.
Published: September 2010

The structure of the title compound was determined by X‐ray analysis, using CuKα radiation, graphite crystal monochromator, λ=1.5418 Å, C17H16, Mr =220.31, monoclinic, space group P21, a=9.0270(9), b=9.5267 (16), c=8.0327(6) Å,β=112.366(7)°, V=638.8 Å3, Z=2, Dc=1.145 Mg/m3, μ(MoKα)=4.92 cm−1, F(000)=236.0, T=290 K. Final conventional R‐factor = 0.044, Rw =0.063 for 2222 unique reflections and 201 variables. The structure was solved by MULTAN.
Crystal and Molecular Structure of Ethyl‐α((E)‐hydroxyimino)‐β‐(2(α,α‐dimethylallyl) indol‐3‐yl)propanoate, C18H22N2O3.1/6 CH2CL2
Authors: Bosman W. P. , Beurskens Paul T. , Smits J. M. M. , Plate Ralf , Ottenheijm Harry C. J.
Published: September 2010

The structure of the title compound was determined by X‐ray analysis, using MOKα radiation, graphite crystal monochromator, λ=0.71069 Å, C18H22N2O3. 1/6 CH2Cl2, Mr=376.53, monoclinic, space group P21/c, a=12.297 (11), b=17.781(6), c=16.612(3) Å,β=93.91(3)°, V=3624(3) Å3, Z=8, Dc=1.35 Mg/m3, μ(MoKα)=1.6 cm−1, F(000)=1399.0, T=290 K. Final conventional R‐factor = 0.096, Rw=0.119 for 3060 unique reflections and 419 variables. The structure was solved by an orientation and translation search on a known fragment and expanded with DIRDIF.
On the relative stabilities of zeolitic silicas
Authors: Ooms G. , van Santen R. A.
Published: September 2010

A simple quantum‐chemical calculation method has been used to obtain a first estimate of the relative stabilities of zeolitic silicas. When applied to dealuminated faujasite, mordenite and ZSM‐5, the method indicated faujasite to be less stable than mordenite and ZSM‐5. However, the calculated differences in heat of formation between the dealuminated zeolites are very small. Hence, care must be taken in drawing any definite conclusions, particularly in view of the rather approximate nature of the calculation method.
Aromatic isomerizations and related reactions. Part 6 Reactions of the tetra‐ and pentamethylbenzenesulfonic acids and hexamethylbenzene in concentrated sulfuric acid; the mechanism of the Jacobsen reaction
Authors: Koeberg‐Telder Ankie , Cerfontain Hans
Published: September 2010

The chemical behaviour of the sulfonic acids of pentamethylbenzene (PMB) and the three tetramethylbenzenes (TeMB's) in concentrated aqueous sulfuric acid has been studied quantitatively using 1H and 13C NMR and UV spectroscopy. PMB‐sulfonic acid yields (protonated) hexamethylbenzene (HMB) and the 2,3,4,5‐ and 2,3,4,6‐TeMB‐1‐sulfonic acids in an initial ratio of 9/1/8 up to a substrate conversion of 36%; the ratio of HMB to the TeMB‐1‐sulfonic acids remains 1/1 and the only subsequent reaction is the relatively slow conversion of the 2,3,4,6‐ into the 2,3,4,5‐TeMB‐1‐sulfonic acid which is the only stable TeMB‐1‐sulfonic acid isomer in concentrated sulfuric acid.

2,3,5,6‐TeMB‐1‐sulfonic acid yields, as initial products, 2,3,5‐ and 2,4,5‐trimethylbenzene(TrMB)‐1‐sulfonic acid together with PMB‐1‐sulfonic acid in a ratio of ca. 1/3/4. The subsequent products are the 2,3,4,6‐ and 2,3,4,5‐TeMB‐1‐sulfonic acids, of which the former slowly isomerizes to the latter, together with some HMB.

2,3,4,6‐TeMB‐1‐sulfonic acid yields the stable 2,3,4,5‐isomer. It is proposed that the conversion proceeds via inter‐molecular trans‐methylations involving 1,3,5‐TrMB and PMB as intermediates, the concentrations of which, however, are below the limits of NMR detection.

Based on (i) the desulfonation‐sulfonation equilibrium data of the TrMB‐, TeMB‐ and PMB‐sulfonic acids, (ii) the strong rate decrease for the conversion of both 2,3,4,6‐ and 2,3,5,6‐TeMB‐1‐sulfonic acid in 98.4% H2SO4 in the presence of added cyclohexane and (iii) the very strong electron‐withdrawing and meta‐directing effect of the SO3−/SO3H substituent, it is proposed that all the conversions proceed inter‐molecularly, that the trans‐methylating reagent is the polymethylbenzene (and not the corresponding sulfonate) and that the substrate undergoing methylation is most likely to be once again the polymethylbenzene rather than its sulfonate ion.
Conformational effects of through‐bond interaction in N‐aryl‐piperidine derivatives
Authors: Krijnen B. , Beverloo H. B. , Verhoeven J. W.
Published: September 2010

Through‐bond interaction in an N‐aryl‐piperidine derivative carrying an electronegative substituent at C‐4 is found to stabilize axial arrangement of the aryl group, which demonstrates the possibility of long‐range stereoelectronic conformational control.
The chemistry of D‐gluconic acid derivatives. Part 1: Synthesis of 3,4;5,6‐di‐O‐isopropylidene‐D‐glucitol and 2,3;4,5‐di‐O‐isopropylidene‐aldehydo‐D‐arabinose from D‐glucono‐1,5‐lactone
Authors: Regeling Henk , de Rouville Egbert , Chittenden Gordon J. F.
Published: September 2010

Acid‐catalysed isopropylidenation of D‐glucono‐1,5‐lactone with 2,2‐dimethoxypropane yields methyl 3,4;5,6‐di‐O‐isopropylidene‐D‐gluconate. Convenient syntheses of the title compounds from this ester by reduction and oxidation sequences, together with the characterisation of the products and intermediates are described.
A specific 2,4‐disubstituted‐adamantane interaction with plasma‐grown aluminium oxide. An inelastic‐electron‐tunnelling spectroscopy study
Authors: Meijer E. W. , Raas M. C. , van Velzen P. N. T.
Published: September 2010

The interaction of several mono‐ and disubstituted adamantanes with plasma‐grown aluminium oxide has been studied using inelastic‐electron‐tunnelling (IET) spectroscopy. The IET spectra evidence the chemisorption of 2,4‐adamantanedione (1) onto the aluminium oxide surface as the carboxylate anion of bicyclic acid ketone 2, which is formed by ring opening of the β‐diketone. In the case of 4‐hydroxy‐2‐adamantanone (3), no ring opening to the corresponding bicyclic acid (4) is observed. 3 is chemisorbed as aluminium alkoxide through condensation. Stabilization by additional hydrogen bonding between the aluminium oxide and the keto group seems to be required since 1‐adamantanol, 2‐adamantanol and 2‐adamantanone do not adsorb onto the aluminium oxide. Even 5‐hydroxy‐2‐adamantanone is not bonded to the surface, indicating the necessity of a specific 2,4‐disubstituted adamantane bidentate interaction with aluminium oxide.
Photochemistry of estra‐5,7‐diene‐3β,17β‐diol 17‐acetate and its 9,10‐seco isomer, 10‐desmethyl analogues of pro‐ and previtamin D. 1. “Reversible” isomerization reactions
Authors: Koolstra R. B. , Cornelisse J. , Jacobs H. J. C.
Published: September 2010

In analogy with the photochemistry of 7,8‐didehydrocholesterol (provitamin D), irradiation of the 10‐desmethyl steroid estra‐5,7‐diene‐3β,17β‐diol 17‐acetate leads to a photoequilibrated mixture of steroid‐5,7‐dienes and 9,10‐seco‐5(10),6,8‐trienes. In addition, a thermally unstable bicyclo[2.2.0]hexene derivative is found. From the composition of the quasi‐photostationary state, the ratios of the quantum yields of the various interconversions are estimated. Differences with the photochemistry in the 10‐methyl series are discussed in relation to conformational differences.
The influence of substituents on the geometry of the cyclopropane ring: III. The molecular and crystal structure of phenylcyclopropane
Authors: de Boer J. S. A. M. , Loopstra B. O. , Stam C. H.
Published: September 2010

Phenylcyclopropane, C6H5C3H5, is monoclinic, with space group Pa, a = 15.761(4), b = 7.748(2), c = 5.854(2) Å, β = 103.01(1)°. V = 696.5(4) Å3 (‐ 100°C). Z = 4. The final R for 1192 independent reflections is 0.039. The two molecules in the asymmetric unit are very similar, the plane of the benzene ring bisecting the cyclopropane ring. The average distal bond length in the cyclopropane ring is 1.502(7) Å; the average vicinal length is 1.520(5) Å (corrected for libration).
An improved procedure for the acetalisation of alcoholic hydroxyl functions
Authors: Roelen H. C. P. F. , Ligtvoet G. J. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Acetalisation of 3′,5′‐di‐O‐acetyluridine in DMF with 4,4‐dimethoxytetrahydro‐4H‐pyran and 4,4‐dimethoxytetrahydro‐4H‐1‐thiopyran in the presence of trimethylsilyl chloride (TMSiCl) afforded, after removal of the acetyl groups, 2′‐O‐(4‐methoxytetrahydropyranyl)‐uridine and its sulfur analogue, respectively. It was also established that a 3′,5′‐O‐(tetraisopropyldisiloxane‐1,3‐diyl) protected ribonucleoside was rapidly isomerised into the corresponding 2′,3′‐isomer using the TMSiCl promoted acetalisation method.
Synthesis of diphosphorylated and diphosphonylated Lipid A monosaccharide analogues via phosphite intermediates
Authors: Westerduin P. , Veeneman G. H. , van Boom J. H.
Published: September 2010

The synthesis of two Lipid A monosaccharide analogues, 3‐O‐palmitoyl‐2‐deoxy‐2‐palmitamido‐α‐D‐glucopyranose 1,4‐diphosphate (1) and the corresponding 1,4‐bis(1H‐phosphonate) (2), is described. The introduction of the phosphate functions was achieved via phosphitylation of the anomeric and non‐anomeric hydroxyl groups with the monofunctional phosphitylating reagents benzyl 2‐cyanoethyl N,N‐diethylphosphoramidite (9) and salicyl phosphochloridite (10). Oxidation of the intermediate phosphite triester and subsequent removal of all the protective groups afforded the target molecules 1 and 2.
Empirical force field calculations. Part 28. Conformations and pseudorotations of 1,3‐dioxolane and some methyl‐substituted derivatives
Authors: van Duin M. , Hoefnagel M. A. , Baas J. M. A. , van de Graaf B.
Published: September 2010

The conformations and pseudorotations of 1,3‐dioxolane (1), cis‐ and trans‐4,5‐dimethyl‐1,3‐dioxolane (2 and 3) and the corresponding 2,2‐dimethyl derivatives (4, 5 and 6) have been studied with molecular mechanics using the MM2 force field. Free pseudorotation occurs in 1 and 4 (ΔE = 1.5 kJ/mol) and pseudolibration in 2, 3, 5 and 6 (ΔE = 6, 7, 11 and 14 kJ/mol, respectively). The steric energies of 3 and 6 are lower than those of 2 and 5 since the 4‐ and 5‐methyl groups can both occupy a pseudo‐equatorial position in the minimum energy conformation of the trans isomers. Estimates of ΔH°f (25°C, gas, kJ/mol) are: 2, ‐ 376.1; 3, ‐ 380.5; 4, ‐ 387.2; 5, ‐ 464.4; 6, ‐ 470.1. Vicinal proton coupling constants were calculated from the appropriate torsion angles and averaged over the pseudorotation circuit. They are in good agreement with experimental values. The 1,3‐dioxolanes can be used as model compounds for borate monoesters of vicinal diols. The 13C chemical shifts of C(2) in 1,3‐dioxolanes correlate well with the 11B chemical shifts in the corresponding borate monoesters.
The (apparently disrotatory) thermal ring opening of 4‐nitro‐1‐cyclobuten‐1 ‐amines
Authors: van Eijk Peter J. S. S. , Overkempe Cor , Trompenaars Willem P. , Reinhoudt David N. , Harkema Sybolt
Published: September 2010

A series of 4‐nitro‐1‐cyclobuten‐l‐amines 3 was isolated from the thermal (2 + 2) cycloaddition of nitro(cyclo)alkenes 1 and ynamines 2. Heating of 3a‐d yielded products corresponding with disrotatory ring opening viz. the 1,3‐dienes 6a‐d. Heating of 3e,f at 60°C gave the dienes 7a,b, as the result of a conrotatory ring opening reaction, together with the trans‐2‐nitrocyclobutenes 8a,b, as the result of a hydrogen shift in the cyclobutene ring. Upon prolonged heating at 80°C 8b was converted into the diene 7b. Treatment of 3e with acid yielded the 2‐nitrocyclobutenes 9a and 9b. The structures of 3a, 3f, 6a and 7b were elucidated by X‐ray analysis. The formation of 6a‐d is attributed to E/Z isomerization of the product, initially formed by a conrotatory ring opening.
Reaction of four‐membered cyclic nitrones with acetyl chlorideα. X‐Ray crystal structures of 2‐[(acetyloxy)amino]‐N,N‐diethyl‐2‐methyl‐4‐oxo‐3‐phenylpentanamide and 1‐acetyl‐3‐chloro‐N, N‐diethyl‐2‐methyl‐4‐methylene‐3‐phenyl‐2‐azetidinecarboxamide
Authors: van Eijk Peter J. S. S. , Trompenaars Willem P. , Reinhoudt David N. , Harkema Sybolt
Published: September 2010

Reactions of the four‐membered cyclic nitrones 1 with acetyl chloride differ strongly from those of other (cyclic) nitrones. In the presence of water, the nitrones 1 yield the 2‐[(acetyloxy)‐amino]‐N,N‐diethylalkanamides 4. The structure of 4b was confirmed by X‐ray analysis. In the absence of water, the N,N‐diethyl‐4‐methylene‐2‐azetidinecarboxamides 5 or the N,N‐diethyl‐2,3‐dihydro‐2‐azetecarboxamides 6 were obtained. X‐ray analysis elucidated the structure of 5a. Under acidic conditions, compounds 5a yielded the 2‐oxa‐5‐azabicyclo[2.1.1]hexan‐3‐one derivative 13. Acid hydrolysis of 6a gave the α‐chloroketone derivative 18 and the 2‐oxopropanamide derivative 19.
Macrocyclic receptor molecules with a pendant carboxylic acid group for the complexation of urea
Authors: Aarts Veronika M. L. J. , Grootenhuis Peter D. J. , Reinhoudt David N. , Czech Anna , Czech Bronislaw P. , Bartsch Richard A.
Published: September 2010

The synthesis of 5,5′‐di‐tert‐butyl‐3‐(carboxymethyl)biphenyl crown ethers and several lariat ethers with pendant carboxylic acid groups, together with the determinations of the pKa values of these crown ether carboxylic acids, are described. In addition, the complexation of urea by these crown ethers has been investigated. Both the larger‐ring biphenyl crown ethers (≥ 29 ring atoms) and lariat ethers (≥ 27 ring atoms) solubilized urea in chloroform. The data for urea complexation by the lariat ethers show that, for assistance in urea complexation, it is important for the carboxylic acid group to be located close to the macrocyclic ring. When the carboxylic acid group of the lariat ethers is located in an appropriate position, urea is complexed by 21–27% of these macrocyclic ligands, as is also the case with the biphenyl crown‐ether carboxylic acids. These results demonstrate that a pendant carboxylic acid group can assist in the complexation of a neutral molecule.
Reactivity of four‐membered cyclic nitrones in 1,3‐cycloaddition reactions. X‐Ray crystal structure of 7‐(2,6‐dichlorophenyl)‐N,N‐diethyloctahydro‐6‐methyl‐1,3‐dioxo‐2‐phenylazeto[1,2‐b]pyrrolo[3,4‐d]isoxazole‐6‐carboxamide
Authors: van Eijk Peter J. S. S. , Verboom Willem , van Veggel Frank C. J. M. , Reinhoudt David N. , Harkema Sybolt
Published: September 2010

The four‐membered cyclic nitrones 1 and 2 react with dimethyl acetylenedicarboxylate to give the corresponding cycloadducts 3,4. Upon reaction of 2a with phenylacetylene, the 5′‐substituted isoxazoline derivative 5 was obtained. Reaction of 2a with methyl propynoate yielded a 1:4 mixture of the 4′‐ and 5′‐cycloadductsδ, 7 and 6, respectively. Reaction of 2a‐c with N‐phenylmaleimide and of 2a with diethyl maleate yielded the corresponding azeto[1,2‐b]pyrrolo[3,4‐d]isoxazole derivatives, 8 and 9, respectively. The exclusive formation of the exo‐conformation of the cycloadducts was unequivocally proven by X‐ray analysis of 8a. Reaction of 2a with methyl 2‐propenoate (methyl acrylate) and 3‐buten‐2‐one (methyl vinyl ketone) gave regio‐ and stereoselectively the corresponding exo‐5′‐isoxazolidine cycloadducts, 10 and 11, respectively. The stereochemistry of the cycloadducts was deduced from the 1H NMR data. Both alkyne and alkene dipolarophiles approach the four‐membered cyclic nitrones from the sterically less hindered side, resulting in a (regio‐ and) stereoselective formation of the cycloadducts obtained.
Transition‐metal coordination compounds of a chelating imidazole‐thioether ligand. The molecular structure of diisothiocyanato[1,6‐bis(5‐methyl‐4‐imidazolyl)‐2,5‐dithiahexane]nickel(II)
Authors: Bouwman E. , de Gelder R. , de Graaff R. A. G. , Driessen W. L. , Reedijk J.
Published: September 2010

The synthesis and characterization of transition‐metal coordination compounds with the novel, tetradentate ligand 1,6‐bis(5‐methyl‐4‐imidazolyl)‐2,5‐dithiahexane (abbreviated bidhx) are described. The nitrates have the general formula M(bidhx)(NO3)2·nH2O (M = Co, Ni, Cu, Zn; n = 0 ‐ 2). With the isothiocyanate anion, monomers M(bidhx)(NCS)2 containing Co, Ni and Zn and Cu(bidhx)(NCS)(NO3) as well as a dimer Cu2(bidhx)(NCS)3 were isolated. In all compounds, bidhx acts as a tetradentate ligand with both thioether sulfurs and both imidazole nitrogens coordinating. All compounds are six‐coordinated in a distorted octahedral geometry, although, for the copper mixed‐anion compound, a five‐coordination in a square pyramidal geometry may also be possible. A single crystal of [Ni(NCS)2(bidhx)](MeOH) was used in a structure determination: monoclinic, space group C2/c, a = 13.0516(7) Å, b = 16.383(1) Å, c = 10.3758(9), Å, β = 101.095(6) deg, Z = 4 and T = 293 K. The structure was solved using heavy‐atom techniques and refined by least‐squares methods to an R value of 0.0508. The nickel ion is in a distorted octahedral environment with the two thiocyanates in a cis position. The nickel to nitrogen distances are ca. 2.04 Å; the nickel to sulfur distances are ca. 2.5 Å.
In situ nucleophilic activation in the propellane 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane and its hydrolysis in solution
Authors: Jurkschat K. , Tzschach A. , Dargatz M. , Pepermans H. , Gielen M. , Willem R.
Published: September 2010

The compound 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane (C9H18NSiCl) combines with water to form an association complex with the formula C9H18NSiCl·H2O. Proton NMR studies at various temperatures, concentrations and magnetic fields indicate that this compound exists in solution as an equilibrium mixture of the initial chloride and its association complex with water, a structure for which is proposed. Evidence is provided against a rigid hexacoordinate complex. The equilibrium is shown to correspond to a reversible hydrolysis of C9H18NSiCl which is nucleophilically activated by the intramolecularly coordinating nitrogen present in situ. The reverse reaction is the decomposition of the association complex C9H18NSiCl·H2O to C9H18NSiCl and free water. As a consequence, this paper presents a reversible hydrolysis of a chlorosilane interconverting two directly observable pentacoordinate species without addition of an external nucleophile, and proceeding with retention of configuration at the silicon atom. We further argue that this reaction cannot proceed through a rigid hexacoordinate octahedral intermediate, but could proceed through two non‐rigid species, the averaged dynamic behaviour of which is identical to a non‐octahedral hexacoordinate transition state.
The primary structure and some kinetic properties of phospholipase A2 from sheep pancreas
Authors: Verheij H. M. , Dijkman R. , de Haas G. H. , Raykova D. , Lenting H. B. M.
Published: September 2010

The complete amino acid sequence of ovine phospholipase A2 (EC 3.1.1.4) has been determined. The enzyme consists of a single polypeptide chain containing 123 amino acids, crosslinked by seven disulfide bridges, with a molecular weight of 13804. The enzyme differs at six positions from phospholipase A2 isolated from bovine pancreas1. Both enzymes show similar affinities for Ca2+ ions and hydrolyze monomeric substrates with comparable efficiency.

Using monomolecular surface films as a substrate, the ovine enzyme was shown to be able to hydrolyze lipids at slightly higher surface pressures than the bovine enzyme. Direct‐binding studies showed the higher affinity of the ovine enzyme for micelles of the substrate analogue, n‐hexadecylphosphocholine.

We suggest that this increased affinity is attributed to a substitution of Asn122 of the bovine enzyme for a tyrosine residue in its ovine counterpart.
Metal ion catalysis in the hydroxyalkylation of phenol with glyoxylic acid
Authors: Hoefnagel A. J. , Peters J. A. , van Bekkum H.
Published: September 2010

The hydroxyalkylation reaction of phenol with glyoxylic acid in aqueous medium is found to be homogeneously catalyzed by various metal ions. Catalysis with MII ions results in a reaction product with an ortho/para ratio of 0.2 to 1.1, whereas catalysis using higher valent cations, because of their ability to form mixed complexes with phenol and glyoxylic acid, affords a reaction product with an ortho/para ratio of 1.3 to 28. The catalyzed Cannizzaro reaction of glyoxylic acid was observed as a side‐reaction. Addition of a suitable inert ligand, e.g. oxalic acid or NTA, is shown to decrease the ortho/para ratio and to suppress the Cannizzaro reaction.

The coordination of glyoxylic acid and its hydrate with several cations has been studied by NMR techniques and a mechanism of the catalyzed hydroxyalkylation and Cannizzaro reaction is proposed.
The crystal structure of dicyclopentadienylmercury
Authors: Fischer Bart , van Mier Guido P. M. , Boersma Jaap , van Koten Gerard , Smeets Wilberth J. J. , Spek Anthony L.
Published: September 2010

Crystals of dicyclopentadienylmercury, Hg(η1‐C5H5)2, are tetragonal, space group I41, with unit cell dimensions a = 17.347(5)Å, c = 5.810(3)Å. The low‐temperature (100 K) crystal structure was solved using Patterson methods and subsequent difference Fourier techniques. Anisotropic full‐matrix least‐squares refinement with 1832 observed reflections and 100 parameters converged at R = 0.0385. In the solid state, dicyclopentadienylmercury consists of monomeric units in which the two cyclopentadienyl rings are covalently bonded to the mercury atom.
Single‐step conversion of aliphatic, aromatic and heteroaromatic primary amines into piperazine‐2,6‐diones
Authors: Kruse C. G. , Troost J. J. , Cohen‐Fernandes P. , van der Linden H. , van Loon J. D.
Published: September 2010

The development of a facile, single‐step method for the synthesis of 1,4‐disubstituted piperazine‐2,6‐diones (4) in excellent yields from the corresponding aliphatic, aromatic and heteroaromatic primary amines and iminodiacetic acids (1) is described. A possible mechanism is discussed and the presence of intermediate 6a is confirmed by high‐resolution proton NMR spectroscopy. The subsequent two‐step conversion of dione 4a into the deoxygenated 4‐unsubstituted piperazine 10 in high yield provides an attractive alternative to the currently available (hetero)arylpiperazine synthetic methods.
Photochemical reactivity of α‐phenyl β,γ‐enones. Singlet 1,3‐acyl shift, triplet aromatic di‐π‐methane (DPM) rearrangement and triplet aryl‐carbonyl bridging
Authors: Koppes Margareth J. C. M. , Beentjes Peter C. J. , Cerfontain Hans
Published: September 2010

The photochemistry of the series of α‐phenyl β,γ‐enones 6–10 has been studied under conditions of both direct (λ 300 nm) and triplet‐sensitized irradiation with the aim of determining the reactivity patterns of these “multi”‐chromophoric systems.

Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ‐enones, viz. the 1,3‐acyl shift, affording the corresponding (E)‐ and (Z)‐5‐phenyl‐4‐hexen‐3‐ones, decarbonylation of the radicals formed by α‐cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet‐excited state yielding small amounts of the corresponding acetophenones. The acetophenones are thought to be formed by initial β‐bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4‐ or 1,3‐oxa‐diradical.

Upon sensitized irradiation, the o‐methoxy‐ and p‐cyano‐substituted reactants 9 and 10 exhibit the di‐π‐methane rearrangement, leading to mixtures of the corresponding cis‐ and trans‐1‐acetyl‐1‐methyl‐2‐phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively. The formation of the 1,3‐AS and decarbonylation products illustrates the occurrence of α‐cleavage, whereas the acetophenones and di‐π‐methane products are formed via initial aryl‐carbonyl and aryl‐vinyl bridging, respectively.

The inability of the other α‐phenyl β,γ‐enones to undergo photocyclopropanation is discussed in terms of excitation‐energy partition. In the o‐methoxy‐ and p‐cyano‐substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ‐enone moiety. Subsequent triplet‐energy dissipation by a free‐rotor mechanism would then account for the stability of these systems. This was observed for (E)‐7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
Intramolecular exciplex formation in jet‐cooled, bichromophoric molecules, II; A dramatic effect of the acceptor electron‐affinity
Authors: Hemant R. M. , Wegewijs B. , Verhoeven J. W. , Kunst A. G. M. , Rettschnick R. P. H.
Published: September 2010

The jet‐cooled fluorescence properties of two bichromophoric molecules (1 and 2), differing only in the acceptor chromophore, are compared. The barrier to exciplex formation in 1, containing a powerful cyanonaphthalene acceptor chromophore, is much lower than that in 2 which contains a less powerful naphthalene acceptor chromophore. It is thus proposed that the barrier is not only of a conformational nature, but also related to the energy required for intramolecular charge separation in the Franck‐Condon excited conformation which may then be followed by a fast, electrostatically‐driven conformational change.
The nucleophilic addition‐elimination reaction on the carbonyl group of pivaloyl chloride, S‐methyl thiopivaloate and 1‐pivaloyl‐1,2,4‐triazole in the gas phase
Authors: van der Wel H. , Bruin G. J. M. , van der Linde S. J. J. , Nibbering N. M. M. , Engberts J. B. F. N.
Published: September 2010

The nucleophilic addition‐elimination reaction on the carbonyl group of the substrates (CH3)3CCOCl, (CH3)3CCOSCH3 and (CH3)3CCON‐CH = N‐N = CH [(CH3)3CCOTAZ] has been studied using Fourier‐Transform Ion‐Cyclotron‐Resonance (FT‐ICR) Mass Spectrometry.

The rates of reactions of (CH3)3CCOCl and (CH3)3CCOSCH3 appear to depend on the basicity of the nucleophiles with the more basic ones reacting most rapidly, while the reactions of (CH3)3CCOTAZ with various nucleophiles occur either at the collision rate for exothermic reactions or not at all for endothermic reactions.

These results are for (CH3)3CCOCl and (CH3)3CCOSCH3 in agreement with a double‐well potential model having the tetrahedral structure as central energy barrier.

The results for the substrate (CH3)3CCOTAZ, however, can be explained very well with a single‐well potential model, where the tetrahedral structure corresponds to an energy minimum.