bluuebunny/crossref_metadata_2025 huggingface dataset:
N, N‐diisopropyl‐bis(4‐chlorobenzyl) phosphoramidite: A versatile phosphitylating agent for the phosphorylation of hydroxy amino acids and preparation of protected phosphopeptides
Authors: de Bont H. B. A. , van Boom J. H. , Liskamp R. M. J.
Published: September 2010

N, N‐diisopropyl‐bis(4‐chlorobenzyl) phosphoramidite is an easily accessible phosphitylating agent, which readily phosphorylates Boc‐Ser‐OMe, Boc‐Thr‐OMe and Boc‐Tyr‐OMe in good to high yields after t‐BuOOH or MCPBA oxidation. The Boc‐group can be removed without affecting the phosphate 4‐chlorobenzyl groups and vice versa. Extension of the Boc‐deprotected phosphoamino acids with a subsequent amino acid yields the corresponding protected phosphopeptides
Dioxygen uptake and catalytic activity of some monomeric copper(II) compounds containing an N,S donor ligand. The X‐ray structure of bis[5‐methyl‐4‐(ethylthiomethyl)imidazole]bis(tetrafluoroborato)copper(II)
Authors: Tullemans A. H. J. , Bouwman E. , de Graaff R. A. G. , Driessen W. L. , Reedijk J.
Published: September 2010

The synthesis and characterization of the copper tetrafluoroborate compound containing the bidentate N,S ligand 5‐methyl‐4‐(ethylthiomethyl)imidazole (memi), [Cu(memi)2(BF4)2], is described. The activities of this compound and of [Cu(memi)2(H2O)2](NO3)2 as oxidation catalysts have been determined in the reaction of 2,6‐dimethylphenol with molecular dioxygen to give polyphenylene oxide (PPO) and diphenoquinone (DPQ). For optimum catalysis, an additional base is required in order to dehydronate the phenol. Triethylamine proved to be most useful as a base. Initial reaction rates encountered are between 1 × 10−5 and 6 × 10−5M O2/s and ca. 50% of the phenol was converted after a reaction time of one hour. Less than 10% phenol was converted into DPQ. Both compounds have comparable reactivities.

A single crystal of [Cu(memi)2(BF4)2] was used in an X‐ray structure determination: monoclinic space group C2/c, a = 13.844(4) Å, b = 11.251(1) Å, c = 15.753(4) Å, β = 111.39 (2)°, Z = 4 and T = 293 K. The structure was solved using heavy‐atom techniques and refined by least‐squares methods to a residual R value of 0.050. The copper ion is in a centrosymmetric distorted octahedral environment with all chemically identical donor atoms in trans positions. The tetrafluoroborate anions are coordinated to the copper ion with relatively short distances, i.e. 2.55 Å; Cu‐N and Cu‐S distances are 1.93 and 2.41 Å.
Highly active heterogeneous rhodium catalysts for the liquid‐phase hydrogenation of aromatic and other unsaturated compounds under mild conditions
Authors: Timmer Klaas , Thewissen D. Harry M. W. , Meinema Harry A. , Bulten Eric J.
Published: September 2010

Highly active heterogeneous rhodium hydrogenation catalysts ‐ rhodium on support ‐ have been prepared by pyrolysis of commercially available Rh4(CO)12, highly dispersed on a suitable support, e.g. SrTiO3, TiO2‐anatase, TiO2‐rutile, BaTiO3 or SrZrO3. The inactive materials initially obtained were activated by exposure to air at room temperature. The activities of these catalysts were determined in the liquid‐phase hydrogenation of aromatic compounds at atmospheric pressure and at low temperatures (max. 70 °C). They appear to be at least twice as active as catalysts prepared from impregnated RhCl3 or [RhCl(CO)2]2 on SrTiO3 or a commercially available catalyst (5% Rh on Al2O3).

The gas‐phase hydrogenation of benzene at room temperature takes place exothermally. Very high activities were also found in the liquid‐phase hydrogenation of alkenes and alkynes, whereas low activities were shown in the hydrogenation of nitriles. Almost no activity was observed in the liquid‐phase hydrogenation of nitro compounds and ketones.

Catalysts, prepared from Rh6(CO)16, showed lower activities as compared with those prepared from Rh4(CO)12. Hardly any activity was found using Ir4(CO)12 as starting carbonyl cluster and no activity was observed when Ru3(CO)12, Co4(CO)12, Os3(CO),2 or Fe3(CO)12 was used.
Study of the promotion effect of inorganic oxides on Pt catalysts for the epoxidation of 1‐octene with hydrogen peroxide
Authors: Strukul Giorgio , Zanardo Andrea , Pinna Francesco , Schmidt Manfred , Goor Gustaaf
Published: September 2010

The promotion effect of a variety of inorganic oxides on the catalytic epoxidation of 1‐octene with hydrogen peroxide catalyzed by (cis‐Ph2PCH = CHPPh2)Pt(CF3)X (X = CH2Cl2, ·OH) in the liquid phase is reported. Catalysts were prepared either by mixing the oxides directly in the reaction medium or by impregnation of the oxides with the complexes prior to catalysis. A significant increase in the catalytic activity is obtained under certain experimental conditions and this is interpreted as a cooperation effect taking place at the interface between solid support and solution.
Steric and electron‐withdrawing effects of substituents governing chemical stability and catalytic activity of Mn(III)‐tetraarylporphyrins in HOCl/ClO− alkene expoxidations
Authors: Banfi S. , Montanari F. , Quici S.
Published: September 2010

Mn(III)‐tetrakis(2,4,6‐trimethyl‐3,5‐dihalogenophenyl)porphyrins 5‐7 (halogen = Cl, Br, I) have been synthesized and their catalytic activity has been tested in HOCl/ClO− alkene epoxidations. These porphyrins are characterized by structural separation of the two parameters governing chemical stability towards the oxidants: the steric protection of both the metal centre and of the meso positions of the porphyrin ring; and the electron‐withdrawing effect of substitutents (methyl groups and halogen atoms in the o,o′ and m,m′ positions, respectively, of the meso‐aromatic rings). The stability of 5–7 towards oxidative degradation is similar to that of Mn(III)‐tetrakis(2,6–dichlorophenyl)porphyrin (1). Catalytic activities of the porphyrins 5‐7 and 1 are optimized under quite different conditions. This behaviour can be explained in terms of mono‐ (K1) and bis‐coordination (β2) constants of porphyrins 1, 5 and 6 with the axial ligand, 1‐hexylimidazole, which account for the concentration of the mono‐ligated species Mn(P)L and of the free ligand at the equilibrium.
Ab‐initio calculations on oxomanganese porphyrin chloride. II. An explanation of its reactions with alkenes
Authors: den Boer D. H. W. , Zwaans R. , van Lenthe J. H. , van der Made A. W.
Published: September 2010

Minimal‐basis‐set gradient‐SCF calculations on oxomanganese porphyrin chloride in which the oxygen atom bridges a metal‐nitrogen bond (Cs structure) are reported. In comparison with the earlier reported results of similar calculations on a C4v structure, a lower energy is found for the Cs structure. Electronic and steric arguments are brought forward to explain available experimental information on the reactions of the complex with alkenes.
Reduction of 1‐(5‐uracilylmethyl)pyridinium salts by thiols to thymine derivatives. A model of the thymidylate synthase reaction
Authors: Vega Erwin , de Waard Eduard R. , Pandit Upendra K.
Published: September 2010

1‐(5‐uracilylmethyl)pyridinium salts react with 9, 10‐dihydrophenanthridine, Hantzsch ester or thiols (RSH, R = p‐nitrobenzyl, t‐butyl) to form thymine derivatives. The mechanisms of the reactions are discussed.
On the mechanism of formation and fragmentation of [8]paracyclophane in the gas phase
Authors: Kraakman Paulus A. , Eeken Paulus J. K. M. , de Wolf Willem H. , Bickelhaupt Friedrich
Published: September 2010

Regiospecifically labelled 3‐[(13C)methylene]spiro[5.7]trideca‐1,4‐diene (2a′) and (1‐13C)‐dispiro[2.2.6.2] tetradeca‐4,13‐diene (7a′) were prepared. By flash vacuum thermolysis (FVT) at 600°C, 2a′ was converted into [8]paracyclophane (1a′) in 95% yield. The label in 1a′ was found at the benzylic position(s). At 750°C, 1a′ fragmented by cleavage of the homobenzylic bonds finally yielding (after extrusion of one or more molecules of propene or ethene) p‐ethyl‐ (4e′) and p‐propyl‐(4d′) styrene. The styrenes were labelled at both benzylic carbon atoms. The product spectrum obtained by FVT of 7a′ was more complex. At 600°C, 1a′, 7a′ and 3‐ vinylspiro[5.6]undeca‐4,13‐diene (11a′) were found. Compound 1a′ was labelled at both the benzylic and homobenzylic positions, whereas 11a′ was labelled only at the two carbon atoms of the vinyl group. At 750 °C, the p‐(n‐alkyl)styrenes 4a′, 4d′ and 4e′, the p‐(sec‐alkyl)styrenes 14d′ and 14e′ and p‐divinylbenzene (15′) were found. Compound 4a′ was labelled only on both carbon atoms of the vinyl group, 4d′ and 4e′ also at the benzylic carbon atom of the alkyl group and 4e′ at the terminal methyl group. The p‐(sec‐alkyl)styrenes 14d′ and 14e′ were labelled exclusively at the benzylic carbon atom and the sec‐methyl group of the sec‐alkyl chain. The distribution of the label in the pyrolysis products is in line with the previously suggested routes for their formation. A full explanation for the (low‐percentage) incorporation of label at some unexpected positions will only be available after further investigation.
A practical route toward the preparation of 4,5:7,8‐di‐O‐isopropylidene KDO ethyl ester
Authors: Boons G. J. P. H. , van der Klein P. A. M. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Condensation of 2,3: 5,6‐di‐O‐isopropylidene‐D‐mannopyranose with (ethoxycarbonylmethylene)triphenylphosphorane afforded the expected Wittig product. Reaction of the latter with chlorotrimethylsilane followed by methyl methanethiosulfate, in the presence of I. DA and after removal of the trimethylsilyl and unmasking of the dimethyl thioketal function, gave the title compound in a good overall yield.
Enantioselective syntheses of isotopically labelled α‐amino acids. Preparation of (ϵ‐13C)‐L‐α‐aminoadipic acid and five isotopomers of L‐lysine with 13C, 15N and 2H in the δ‐ and ϵ‐positions
Authors: Raap J. , van der Wielen C. M. , Lugtenburg J.
Published: September 2010

An asymmetric synthesis of the six‐carbon α‐amino acids (ϵ‐13C)‐L‐α‐aminoadipic acid and various isotopomers of L‐lysine is described. The synthesis is based on a general method starting from the bis‐lactim ether of cyclo(D‐Val‐Gly) and simple labelled reagents like K13CN, K13C15N, 13CH3CN and LiAl2H4. Using this route (ϵ‐13C)‐L‐α‐aminoadipic acid was prepared in 31% yield based on the labelled potassium cyanide. Five different isotopomers of L‐lysine were prepared in high overall yield (45% based on the labelled starting compound): (ϵ‐13C)‐L‐lysine, (ϵ‐13C,ϵ‐15N)‐L‐lysine, (δ‐13C)‐L‐lysine, (ϵ‐2H2)‐L‐lysine and (ϵ‐13C,ϵ‐2H2)‐L‐lysine. The isotopomers were characterized using various spectroscopic techniques, e.g., 1H NMR, 2H NMR, 13C NMR, 15N NMR and mass spectrometry. The 31.2‐ppm and the 27.6‐ppm peak in the 13C NMR spectrum of lysine could be unambiguously assigned to the β‐ and δ‐carbons, respectively. This means that the assignment previously reported is incorrect.
Photoreduction of aryl ketones by amides, lactams and various nitrogen‐containing heterocycles
Authors: Gramain Jean‐Claude , Remuson Roland , Jeandrau Jean‐Pierre , Lemaire Jacques
Published: September 2010

Benzophenone is photoreduced by amides and lactams. The hydrogen atom α to the nitrogen atom is abstracted regioselectively; coupling of the two resulting radicals leads to adducts with a 1‐phenylethanolamide structure. The use of this general reaction in synthetic reactions is demonstrated: adducts of benzophenone with amides, lactams, 2,4‐imidazolinediones tetrahydro‐2H‐1,3‐oxazin‐2‐one and 2‐oxazolidinone, and of dibenzosuberone, 9H‐xanthenone, 9H‐thioxanthenone and α‐tetralone with 1‐methyl‐2‐pyrrolidinone, N,N‐dimethylacetamide and N,N‐diethylacetamide are described. Kinetic parameters for dibenzosuberone and 9H‐thioxanthenone are given. Knowledge of the rate constants of photoreduction (kr) and autodeactivation (kaT) allows optimization of the experimental procedure to provide adducts in good yields.
Gas‐phase oxygenation of benzene derivatives around 300 K with O(3P) atoms produced by microwave discharge of N2O. Part 2. Kinetic H/D isotope effects
Authors: Sol Veronica M. , Louw Robert , Mulder Peter
Published: September 2010

The possible pathways for the formation of (chloro)phenol, following the addition of O(3P) to (chloro)benzene, have been examined using deuterated substrates: C6D6 (also in admixture with C6H6) and p‐deuterochlorobenzene. Whereas with O‐C6H6 adduct biradicals, loss of H\documentclass{article}\pagestyle{empty}\begin{document}\[^\bullet\]\end{document} to give phenoxy radicals predominates, only one‐third of the O‐C5D6 intermediates undergo the corresponding reaction. Phenoxy radicals lead to phenol by transfer of an H(D) atom from cyclohexadienyl‐type radicals, formed from H\documentclass{article}\pagestyle{empty}\begin{document}\[^\bullet\]\end{document} (D\documentclass{article}\pagestyle{empty}\begin{document}\[^\bullet\]\end{document}) and substrate.

Analogously, in reactions of p‐deuterochlorobenzene, loss of H is a major reaction after addition of an oxygen atom to a meta position, whereas loss of D (to give p‐chlorophenol) occurs only with 35% of the corresponding O(3P) adduct biradicals. The isotopic composition of phenol formed from p‐DC6H4Cl (via p‐DC6H4O\documentclass{article}\pagestyle{empty}\begin{document}\[^\bullet\]\end{document}; generated by ipso substitution) revealed that H transfer to phenoxy radicals primarily gives the keto tautomers as major products. Isomerization of (chloro)‐benzene‐O(3P) adduct biradicals to the corresponding phenols also appears to involve mainly, keto tautomers.

The reaction of O(3P) with p‐deuterochlorobenzene showed a slight change in the o/m/p distribution; this can be explained by the absence of a net secondary H/D kinetic isotope effect for O(3P) addition to the para site and a normal secondary isotope effect for meta addition.
Intramolecular amine coordination versus NMe C‐H Activation: The stereoselective synthesis of a tantala(V)azacyclopropane complex
Authors: Abbenhuis Hendrikus C. L. , Grove David M. , van Mier Guido P. M. , van Koten Gerard , Spek Anthony L.
Published: September 2010

A stereoselective C‐H activation reaction of a NMe group of [Ta{C6H4CH(Me)NMe2−2}‐(CH2Ph)2Cl2 (1b) affords toluene and a species which was isolated as the new pentagonal bipyramidal Ta(V) tetrahydrofuran (THF) adduct [Ta{C6H4(CH(Me)N(Me)CH2)‐2}(CH2Ph)Cl2‐ (THF)] (2). The chirality of the arylamine leads to a single structurally characterized diastereoisomer in which intramolecular coordination of the modified amine group produces a triangular Ta‐CH2‐N unit.
The influence of substituents on the geometry of the cyclopropane ring. IV. The molecular and crystal structure of 1‐amino‐1‐phenylcyclopropane
Authors: de Boer J. S. A. M. , Stam C. H.
Published: September 2010

Crystals of 1‐amino‐1‐phenylcyclopropane, C9H11N, grown from the liquid are mono‐clinic, space group P21/n, a = 27.565(5), b = 6.047(6), c = 18.024(4) Å, β = 96.76(2) = (110 K). Z = 16. The final R for 4086 independent observed reflections is 0.057. The 4 molecules in the asymmetric unit have the bisecting conformation for the phenyl group and the s‐trans pyramidal conformation for the NH2 group. The average distal bond length in the cyclopropane ring is 1.503(4) Å; the average vicinal length is 1.520(3) Å (corrected for libration).
Crown‐ether‐substituted phthalocyanines. Control of supramolecular organization by monovalent and divalent metal salts
Authors: Sielcken Ot E. , Drenth Wiendelt , Nolte Roeland J. M.
Published: September 2010

Aggregation of crown‐ether‐substituted phthalocyanines with monovalent metal ions (K+, Rb+, and Cs+) results in cofacially ordered phthalocyanine stacks. Aggregation with Ba2+ leads to the formation of phthalocyanine networks.
Two‐step chemo‐enzymatic synthesis of octyl 6‐O‐acyl‐α‐D‐glucopyranoside surfactants from glucose
Authors: de Nijs M. P. , Maat L. , Kieboom A. P. G.
Published: September 2010

Three novel carbohydrate surfactants were synthesized by lipase‐catalyzed transesterification of octyl 2‐D‐glucopyranoside, obtained from the acid‐catalyzed reaction of glucose and octanol. The 6‐OH was regioselectively acylated with ethyl octanoate, ethyl acetoacetate and diethyl succinate as acyl‐donating agents. Several lipases have been investigated as biocatalysts. For each esterification, various combinations of lipase, ester and cosolvent were studied, from which a preparative‐scale synthesis was developed. The new compounds were tested for physical properties (melting behaviour, surface tension and CMC): it appears that all 6‐acyl derivatives have surfactant characteristics. The 6‐octanoyl derivative was also found to have liquid‐crystal properties.
The synthesis of polyhydroxycarboxylates. Part 6. N‐Alkylation of amino compounds by a Michael‐type addition with maleate
Authors: van Westrenen J. , van Haveren J. , Alblas F. J. , Hoefnagel M. A. , Peters J. A. , van Bekkum H.
Published: September 2010

The N‐alkylation of aminopolyols and amino acids by a Michael‐type addition with maleate or fumarate in aqueous medium occurs readily at 90°C. Maleate reacts faster than fumarate by virtue of the higher free energy of the ground state. For a series of amino compounds, the second‐order rate constants are related to the nucleophilicity of the nitrogen and the steric hindrance involved. Subsequent N‐alkylation of aminohydroxyl compounds and LaIII‐ion‐catalyzed O‐alkylation of hydroxyl groups with maleate is shown to be a promising way to synthesize new chelating agents.
Photochemical behaviour of cyclic s‐cis α‐oxo oxime ethers. Ab‐initio investigation on ethanedial monooxime as model compound
Authors: Stunnenberg Frank , Rexwinkel Roel , Cerfontain Hans , Sevin A.
Published: September 2010

With the objective of understanding the photodissociation of cyclic s‐cisoid α‐oxo oxime ethers upon irradiation at λ 254 nm, an ab‐initio study has been performed using s‐cis‐ethanedial monooxime as model compound. In accordance with previously presented experimental observations, the calculations demonstrated (i) that the initial step in the photodissociation is NO homolysis and (ii) that NO scission takes place with the (E), but not with the (Z) isomer, due to the presence of a relatively low‐lying doubly excited (nπ*)(nπ*) state with the (Z) isomer, causing this isomer to decay via Z‐E isomerization.
Photochemistry of α‐oxo oximes. Part 11: Photochemical E‐Z isomerization of two 2‐(methoxyimino)‐1‐indanones. Evidence for excimer formation upon direct excitation at λ 300 nm
Authors: Buys Theo S. V. , Cerfontain Hans , Geenevasen Jan A. J.
Published: September 2010

Photochemical E‐Z isomerization of 2‐(methoxyimino)‐1‐indanone (1) and its 7‐methyl derivative (2) was studied under conditions of direct irradiation (λ 350 and 300 nm) and triplet photosensitization. The decay ratios k5/k6 for triplet photosensitization and direct irradiation at λ 350 nm are the same for a given compound, indicating that isomerization of the studied α‐oxo oxime ethers upon direct irradiation at λ 350 nm also proceeds from the (lowest) excited triplet state. Upon direct irradiation at λ 300 nm, the photostationary state (pss) was found to depend on the concentration of the 2‐(methoxyimino)‐1‐indanone: at high concentrations, the (E)‐isomer strongly dominates (>90%), whereas, at low α‐oxo oxime ether concentrations, a substantial amount of the (Z)‐isomer is present (up to 35%). The concentration dependence of the pss is explained in terms of excimer formation of the S2(ππ*) state, the excimer being capable of inducing efficient E‐Z isomerization with a different decay ratio than that of the excited triplet monomer.
Gas‐phase reactions of benzene and derivatives triggered by hydrazine/ozone; hydroxylation vs. degradation
Authors: Sol Veronica M. , Mulder Peter , Louw Robert
Published: September 2010

The reactions of benzene derivatives C6H5X (X = H, Cl, CH3 and CF3) with hydrazine and ozone in the dark (a source of OH radicals) have been studied in a flow reactor at ambient temperature.

(Substituted) phenols were formed, but these were relatively unimportant compared to N‐heterocyclic compounds (condensation products of cis‐butenedial and analogues with hydrazine) and other (degradation) products.

Benzene and (trifluoromethyl)benzene follow a similar path as toluene, also with oxidative ring opening as major reactions.
He I and He II photoelectron spectra and semi‐empirical calculations on the three geometric isomers of 3,3,4,4‐tetramethyl‐1,2‐bis(methoxyimino)cyclobutane
Authors: Stunnenberg Frank , Cerfontain Hans , Terpstra Andries
Published: September 2010

The experimental (PES) and calculated (MNDO) ionization potentials of the three geometric isomers of 3,3,4,4‐tetramethyl‐1,2‐bis(methoxyimino)cyclobutane [E,E)‐, (E,Z)‐ and (Z,Z)‐1] are reported. The derived electronic structures are compared with those of the three isomeric five‐membered ring homologues 2. The three different orientations of the two methoxy groups in 1 have only a small effect on the energy of the π levels since the three isomers of 1 are planar [or, as in the (Z, Z)‐isomer, almost so], but they have a significant effect on the order of the n+ and n− levels. The variations in the lone‐pair order are discussed in terms of through‐bond and through‐space interactions.
Controlled hydrolysis, an important side reaction in phosphazene chemistry
Authors: Brandt Krystina , van de Grampel Johan C. , Meetsma Auke , Jekel Andries P.
Published: September 2010

Reaction of (NPCl2)3 (1) with the monosodium salt of uracil in the presence of Bu4NBr as phase‐transfer catalyst gives apart from an uracil phosphazene derivative (N3P3Cl5)2C4N2H2O2 (2) appreciable amounts of two hydrolysis products, viz. [N3P3Cl5O] [Bu4N] (3) and an oxygen‐bridged dimer (N3P3Cl5)2O (4). 31P NMR data are given as well as the X‐ray structure of 4.
Photochemistry and spectroscopy of three α‐oxo oxime ethers: 4‐(methoxyimino)‐2,2,3,3‐tetramethylcyclobutanone, 3,3,5‐trimethyl‐4(5H)‐isoxazolone and 6‐(benzyloxyimino)‐2,2,5,5‐tetramethylcyclohexanone
Authors: Stunnenberg Frank , Cerfontain Hans , Geenevasen Jan A. J. , Hielkema Wim
Published: September 2010

Following our previous reports on the spectroscopy and photochemistry of methyl and ethyl ethers of simple acyclic and non‐strained cyclic α‐oxo oximes, we have now studied 4‐(methoxyimino)‐2,2,3,3‐tetramethylcyclobutanone (1), of which the ring is severely strained, 3,5,5‐trimethyl‐4(5H)‐isoxazolone (8), of which the (Z)‐oxime function is constrained in a five‐membered ring, and 6‐(benzyloxyimino)‐2,2,5,5‐tetramethylcyclohexanone (10), which is a benzyl ether. Upon irradiation of (E)‐1 with λ 254 nm, the main process is photodissociation, leading to the same type of products as obtained with the six‐membered ring homologue 3, but in addition to 2,2,3,3‐tetramethyl‐4‐oxobutanenitrile (13) and 2,2,3,3‐tetramethylcyclopropanone O‐methyloxime (21). The triplet‐sensitized irradiation of (E)‐l, in contrast to that of the higher homologues, leads, in addition to E‐Z isomerization, to photodissociation, yielding the same photoproducts as obtained after direct irradiation with 254 nm.

The 4‐isoxazolone 8 is photostable against radiation of 350 and 300 nm. Irradiation of 8 with λ. 254 nm leads to population of the excited singlet ππ* state and subsequent photodecomposition as a result of inital N‐O homolysis, the observed products being carbon monoxide, acetonitrile, acetone and small amounts of ethanol. The occurrence of the photodecomposition is in agreement with the theoretical prediction' that the excited singlet ππ* (Z)‐α‐oxo oxime ethers would give N‐O homolysis, provided that the other route of deactivation via Z‐E isomerization, which has a much lower energy barrier on the potential energy surface, cannot take place.

The photochemistry of the benzyl ether (Z)‐10, of which the intercarbonyl‐iminyl dihedral angle is approx. 45° and the π systems of the phenyl and the C = N‐O moieties are perpendicular to one another, with λ 350, 300 and 254 nm is different from that of the corresponding methyl ether 36 in two ways. Firstly, on using λ 350 and 300 nm decomposition was observed which is, however, slow relative to the Z‐E isomerization and, secondly, the photodecomposition products are of a different nature, since the assigned primary and secondary product from 10 are benzaldehyde and 6‐(benzoylamino)‐2,2,5,5‐tetramethylcyclohexanone (32), respectively.

Mechanisms have been presented to explain the formation of the photoproducts obtained from 1, 8 and 10.
Synthesis of potential UDP‐glucuronosyltransferase inhibitors containing a diphosphate function
Authors: Noort D. , van der Marel G. A. , van der Gen A. , J. H.  , Mulder G. J.
Published: September 2010

The synthesis of potential inhibitors of UDP‐glucuronosyltransferase, in which the β‐phosphate moiety of uridine 5′‐diphosphate is linked to phenolic or alcoholic hydroxyl groups, is described. Key intermediates in the formation of the diphosphate function are S‐(4‐methylphenyl) 2‐cyanoethyl phosphorothioate triesters which, after conversion into the corresponding S‐(4‐methylphenyl) phosphorothioate diesters, react with phosphate monoesters, in the presence of iodine, to give the target molecules.
Acylium salts: Synthesis of tris(3,4,5,6‐tetrahydro‐1,3,5‐triazinium) and tris(1,3,5‐oxadiazinium) salts
Authors: Tashtoush Hasan , Al‐Talib Mahmoud
Published: September 2010

Triacylium salts 5 reacted with nine equivalents of dialkylcarbodiimide to give substituted tris(3,4,5,6‐tetrahydro‐1,3,5‐triazinium) salts 6a‐e. However, triacylium salts 5 reacted with six equivalents of N,N‐dialkylcyanamide to give amino‐substituted tris(1,3,5‐oxadiazinium) salts 7a‐e.
1H‐ and 13C‐NMR spectroscopy of synthetic monosulfated methyl α‐D‐mannopyranosides
Authors: Contreras Raphael Ruiz , Kamerling Johannis P. , Vliegenthart Johannes F. G.
Published: September 2010

The syntheses of methyl α‐D‐mannopyranoside 2‐, 3‐, 4‐, and 6‐(sodium monosulfate) are presented. The various monosulfated methyl α‐D‐mannopyranosides have been studied by 1H‐ and 13C‐NMR spectroscopy, affording insight into the 1H‐ and 13C‐shift effects caused by sulfation at particular positions. The NMR parameters of these sulfated monosaccharide derivatives are important, for example, in the structural analysis of sulfated carbohydrate chains of N‐glycoproteins.
An approach toward the synthesis of racemic myo‐inositol 1‐([S] 3,4‐di‐palmitoyloxybutyl)‐sulfonate
Authors: Elie C. J. J. , Dreef C. E. , Brounts D. M. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Substitution of the triflate function in 1,2‐isopropylidene‐sn‐glycerol 3‐trifluoromethanesulfonate by the α‐lithio‐anion of 2,3,4,5,6‐penta‐O‐benzyl‐myo‐inositol 1‐methanesulfonate afforded, after acid hydrolysis of the acetonide function, followed by palmitoylation and removal of the benzyl groups, the racemic and isosteric methylenesulfonyl analogue IV of phosphatidyl‐D‐myo‐inositol.
Catalytic hydrogenation of D‐xylo‐5‐hexulosonic acid to gluconic and idonic acid
Authors: Caldeira M. M. , Wurtz E. , Peters J. A. , van Bekkum H.
Published: September 2010

The influence of the choice of catalyst and the presence of additives on the selectivity of the hydrogenation of D‐xylo‐5‐hexulosonic acid was investigated. Optimal amounts of idonic acid were obtained with palladium boride as the catalyst in aqueous solution at pH 9, 80 °C and 100 kg/cm2 H2. Under these conditions, the conversion is 100% and the molar ratio of idonic and gluconic acid in the reaction product is 3/1, whereas almost no side products (<5%) were formed.
Stereochemical aspects of the “tert‐amino effect”. Controlled cycloreversion of pyrrolo[1,2‐α]quinoline derivatives and enantioselective introduction of two new optically active centers
Authors: Kelderman E. , Noorlander‐Bunt H. G. , Verboom W. , Reinhoudt D. N. , van Eerden J.
Published: September 2010

Conversion of 2‐vinyl‐N,N‐dialkylanilines 2,3(a‐o) to pyrrolo[1,2‐α]quinolines 4–13 (a‐o) occurs via an irreversible suprafacial 1,5 hydrogen shift to a dipolar intermediate which subsequently cyclizes. In refluxing acetonitrile in the presence of zinc chloride, pyrrolo[1,2‐a]quinoline derivatives having two electron‐withdrawing groups (EWG) at C(4) show cycloreversion. Because of the longer lifetime of the stabilized dipolar intermediate, epimerization at C(4) and/or C(3a) can occur. Epimerization at C(3a) is prevented by a large methoxymethyl substituent at this stereocenter. Since the initial 1,5 hydrogen shift is irreversible, the stereochemistry at C(5) remains unchanged. In product 4j, two new optically centers at C(5) and C(4) were introduced in a controlled manner and at C(3a) “self‐reproduction of chirality” was obtained without the use of auxiliary chiral reagents.
Formation of pentafulvene in flash vacuum thermolysis of 5‐[7‐(2‐norbornenylidene)] meldrum's acid over bituminous carbon: Evidence for cyclopentadienylidene carbene
Authors: Wiersum Ulfert E. , Jenneskens Leonardus W.
Published: September 2010

The formation of pentafulvene (12)and benzene (11) upon flash vacuum thermolysis of 5‐[7‐(2‐norbornenylidene)] Meldrum's acid (9) over a hydrogen donating bituminous carbon matrix, provides the first experimental evidence for the occurrence of cyclopentadienylidene carbene (2) as a discrete species on the C6H4. energy surface.
A new synthetic methodology for 1,3‐diynes
Authors: Brandsma L. , Verkruijsse H. D. , Fossatelli M.
Published: September 2010

1,3‐Diyne derivatives, (3) and related highly unsaturated compounds have been obtained with excellent overall yields by functionalization of the readily available 1‐ethylthio‐1,3‐butenyne (1) followed by reaction of the derivatives (2) with sodamide in liquid ammonia.
Reversible carbonylation of cationic palladium 2,6‐bis[(dimethylamino)methyl]pyridine complexes: The first X‐ray structure of a cationic aroyl‐palladium complex
Authors: Markies Bertus A. , Wijkens Peter , Boersma Jaap , van Koten Gerard , Spek Anthony L.
Published: September 2010

(1‐Naphthyl)(2,6‐bis[(dimethylamino)methyl]pyridine}palladium(II) trifluoromethanesulphonate (1b, [Pd(1‐C10H7)(NN′N)]OTf) was prepared in 60% yield starting from bis(dibenzylideneacetone)palladium(0) (Pd(dba)2) and 1‐iodonaphthalene. (1‐Naphthoyl){2,6‐bis[(dimethylamino)methyl]pyridine}palladium(II) trifluoromethanesulphonate (2b, [Pd(C(O)‐1‐C10H7)(NN′N)]OTf), characterized by X‐ray crystallography, was obtained by insertion of carbon monoxide into the palladium‐carbon bond of lb in acetone solution. This insertion process was shown to be reversible.
Chemo‐enzymatic synthesis of specifically stable‐isotope labelledL‐glutamic acid and 2‐oxoglutaric acid
Authors: Cappon J. J. , Baart J. , van der Walk G. A. M. , Raap J. , Lugtenburg J.
Published: September 2010

(3‐13C)‐, (4‐13C)‐, (5‐13C) and (3,4‐13C2)‐2‐oxoglutaric acid were prepared starting from the simple 13C‐enriched compounds: ethyl bromoacetate and paraformaldehyde, via a single reaction scheme on the gram scale in high yield. This reaction scheme allows specific 13C enrichment of every carbon position and any combination of positions. (3‐13C)‐, (4‐13C)‐, (5‐13C), (3,4‐13C2) and (15N)‐L‐glutamic acid were prepared by converting the corresponding 2‐oxoglutaric acids via an enantioselective enzymatic conversion. The labelled L‐glutamic acids and 2‐oxoglutaric acids were characterized by 1HNMR, 13CNMR and mass spectrometry.
Acceleration of enzyme‐catalyzed reactions in organic solvents by crown ethers
Authors: Broos Jaap , Martin Marie‐Noëlle , Rouwenhor Inge , Verboom Willem , Reinhoudt David N.
Published: September 2010

Crown ethers can strongly enhance the transesterification of N‐acetyl‐1‐phenylalanine ethyl ester with 1‐propanol catalyzed by α‐chymotrypsin in various organic solvents. Of the different crown ethers tested, 18‐C‐6 gave the best results. It was found that a macrocyclic effect is responsible for the observed rate enhancement. It is proposed that the water‐ and cation‐complexing ability of crown ethers plays a key role in the observed rate enhancement.
Nucleophilic substitution in diphenylmethyl derivatives. II. Methanolysis of α substituents of diphenylacetic acid and its derivatives
Authors: Strazzolini Paolo , Poiana Marco , Verardo Giancarlo , Giumanini Angelo G.
Published: September 2010

The nucleophilic displacement of α substituents of diphenylacetic acid and its methyl ester by MeOH under a variety of experimental conditions allowed us to establish that the reaction occurs rapidly in one of the following structural combinations: (a) carboxylate anion and a good leaving group; (b) carboxylic group and a less reactive leaving group; (c) methyl ester and proton‐activated, poor leaving group. The importance of internal hydrogen bonding (case b) was the governing factor in the outcome of the reaction of hydroxydiphenylacetic acid (3a) and its methyl ester 3b with acetyl chloride. The key intermediate in substitution at the α carbon is thought to be a carbocation stabilized both by the attached phenyl groups and, to a smaller extent, by the carboxyl group.
The influence of substituents on the geometry of the cyclopropane ring. V. The molecular and crystal structure of 1‐amino‐1‐methylcyclopropane
Authors: de Boer J. S. A. M. , Stam C. H.
Published: September 2010

Crystals of 1‐amino‐1‐methylcyclopropane, C4H9N, grown from the liquid, are tetragonal, space group I41/a, a = 18.142(3), c = 5.882(1) Å, (169K), Z = 16. The final R for 733 independent observed reflections is 0.040. The molecule has the s‐trans pyramidal conformation for the amino group. The bond‐length asymmetry induced by the substituents is small and about equal to that in aminocyclopropane. The average CC bond length is 1.513 Å (corrected for libration).
A study on the use of phenylacetyl disulfide in the solid‐phase synthesis of oligodeoxynucleoside phosphorothioates
Authors: Roelen H. C. P. F. , Kamer P. C. J. , van den Elst H. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Sulfurization of protected [i.e., 2‐cyanoethyl, methyl and 2‐(4‐nitrophenyl)ethyl] internucleosidic phosphite triesters can be conveniently executed with the easily accessible reagent, phenylacetyl disulfide (1). High‐quality oligodeoxynucleotides containing predetermined combinations of natural and phosphorothioate linkages can be obtained via a solid‐phase approach by using reagent 1 and 2‐(4‐nitrophenyl)ethyl‐protected phosphoramidites.
Formation of 1,2,4‐benzenetriol by hydrothermal treatment of carbohydrates
Authors: Luijkx G. C. A. , van Rantwijk F. , van Bekkum H.
Published: September 2010

Conversion of dilute aqueous solutions of 5‐hydroxymethyl‐2‐furaldehyde and D‐fructose under near‐critical conditions led to the formation of 1,2,4‐benzenetriol in relatively high yields.
The use of phosphorus oxychloride in the synthesis of amino acid p‐nitroanilides
Authors: Rijkers D. T. S. , Hemker H. C. , Nefkens G. H. L. , Tesser G. I.
Published: September 2010

Phosphorus oxychloride is described as a condensing agent in the preparation of nitroanilides. The condensation was free of racemization with amino acid derivatives of the urethane type and the current amino protective groups can be applied. The yields are high to excellent.
Fluorescence of and photoinduced electron injection into the C70 fullerene chromophore
Authors: Verhoeven Jan W. , Scherer Taco , Heymann Dieter
Published: September 2010

The fluorescence of the C70 fullerene chromophore in three solvents is reported. Quenching of this fluorescence by organic electron donors occurs as a result of photoinduced electron transfer. With aniline‐type donors ground‐state charge transfer complex formation is evident from curved Stern‐Volmer plots as well as from additional long wavelength absorption.
Cation exchange in the system CaII or MgII + complexing‐agent + zeolite‐NaA: Equilibria in water‐ethanol
Authors: Ebaid A. R. , Barakat A. K. , Khalifa N. A. , Kandil A. T. , Maesen Th. L. M. , van Bekkum H.
Published: September 2010

The ion‐exchange behaviour of CaII and MgII with zeolite NaA in ethanol‐water systems has been studied. The ion‐exchange isotherms show that the affinity of the zeolite for CaII and MgII ions decreases with increasing ethanol content, i.e. decreasing dielectric constant of the media. When adding nitrilotriacetate (NTA) as a complexing agent, the selectivity of zeolitic NaA for CaII and MgII ions was found to decrease. The exchange phenomena observed are discussed in relation with water distribution and cation coordination preferences. Cation‐anion coordination in mixed solvents was studied using 35Cl NMR.
Fluorescence spectroscopic study of the formation of hydrophobic microdomains in aqueous solutions of poly(alkylmethyldiallylammonium bromides)
Authors: Yang Ya Jiang , Engberts Jan B. F. N.
Published: September 2010

The conformational state of poly(alkylmethyldiallylammonium bromides) was studied in aqueous solutions using pyrene as a fluorescence probe. The results are indicative for the formation of hydrophobic microdomains in the case of several copolymers which possess sufficiently hydrophobic alkyl side chains. For these materials the polymer main chain is flexible enough to form a compact‐coil conformation which allows intramolecular micellization. The effect of temperature and of the addition of NaBr and DMSO on microdomain formation was briefly investigated.
Studies on the conversion of 3,3‐dimethyl‐2‐butanone into geminal isocyano tosyl alkenes
Authors: van Leusen Daan , van Leusen Albert M.
Published: September 2010

3,3‐Dimethyl‐2‐butanone (pinacolone) was converted in a two‐pot, three‐step process in 67% overall yield into (E)‐1‐isocyano‐2,3,3‐trimethyl‐1‐tosyl‐1‐butene (1), or 1‐isocyano‐3,3‐dimethyl‐2‐methylene‐l‐tosylbutan(2), as an important departure from the previously reported one‐pot conversion to 2,3,3‐trimethylbutanenitrile (13). In addition, the synthesis procedure for 13 has been improved.
An alternative synthesis of (+)‐sesbanimide A
Authors: Vloon W. J. , van Den Bos J. C. , Willard N. P. , Koomen G.‐J. , Pandit U. K.
Published: September 2010

D‐(+)‐xylose has been converted to (+)‐sesbanimide A in sixteen steps. The synthetic scheme involves an unusual tricyclic silylated derivative (9a) of the monobenzoylated product of the earlier described glutarimide intermediate (7). Compound 9a is a pivotal intermediate for the construction of ring C of (+)‐sesbanimide A.
Regioselective synthesis of nucleopeptidic bioconjugates enzymatic catalysis with ultrasonic irradiation
Authors: Criton Marc , Dewynter Georges , Montero Jean‐Louis
Published: September 2010

The regioselective acylation of adenosine by phenylalanine was carried out using subtilisin in reverse mode. Under ultrasonic irradiation, the bioconversion affords only the S' aminoester.
Synthesis of (3′→5′) methylene acetal linked dinucleosides containing cytosine bases
Authors: Quaedflieg P. J. L. M. , van der Marel G. A. , Kuyl‐Yeheskiely E. , van Boom J. H.
Published: September 2010

5′‐O‐Methoxyacetyl‐3′‐O‐methylthiomethylene‐2′‐deoxy‐uridine could be condensed with 3′‐O,N3‐di‐benzoyl‐thymidine using NIS I cat. TfOH as the activating system, to give the (3′→ 5′) methylene acetal linked dinucleoside. After removal of the methoxyacetyl group and tritylation of the 5′‐hydroxyl function, the uridine moiety was converted into cytidine via the corresponding 4‐triazolo analogue. Subsequent N4‐benzoylation of cytidine and phosphitylation of the 3′‐terminus afforded the fully protected d(C∧T) phosphoramidite dimer 9.
New developments in thermally stable polymers
Authors: Hergenrother Paul M.
Published: September 2010

Advances in high‐temperature polymers since 1985 are discussed with the emphasis on the chemistry. High‐temperature polymers refer to materials that exhibit glass‐transition temperatures > 200°C and have the chemical structure expected to provide high thermooxidative stability. Specific polymers or series of polymers were selected to show how the chemical structure influences certain properties. Poly(arylene ethers) and polyimides are the two principal families of polymers discussed. Recent work on poly(arylene ethers) has concentrated on incorporating heterocyclic units within the polymer backbone. Recent polyimide work has centered on the synthesis of new polymers from novel monomers, several containing the trifluoromethyl group strategically located on the molecule. Various members in each of these polymer families display a unique combination of properties, heretofore unattainable. Other families of polymers are also briefly discussed with a polymer from an AB maleimidobenzocyclobutene exhibiting an especially attractive combination of properties.
Synthesis of functionalized phenylalanine derivatives by ring opening reactions of 3‐arylaziridine‐2‐carboxylic esters
Authors: Legters Johan , Thijs Lambertus , Zwanenburg Binne
Published: September 2010

Ring‐opening reactions of 3‐arylaziridine‐2‐carboxylic esters with various nucleophiles are described. Racemic methyl 3‐(4‐methoxyphenyl)‐, 3‐phenyl‐ and 3‐(4‐nitrophenyl)aziridine‐2‐carboxylate (1a, 1b and 1c, respectively) were selected as substrates. In the absence of acid, no ring opening occurred. On treatment with ethereal hydrogen chloride, 1a gave a mixture of diastereomers 2a, whereas 1b and 1c gave mixtures of regioisomers 2b/3b and 2c/3c, respectively. Boron‐trifluoride etherate catalyzed reaction of 1a with benzenethiol and indole also resulted in the formation of diastereomeric ring‐opened products 4a and 6a, respectively, due to the electron‐releasing properties of the p‐methoxy group. Only C3 attack was observed. Under the same conditions, 1b and 1c gave a clean SN2‐type ring opening, leading to diastereomerically pure products 4b, 4c, 6b and 6c. Reaction of 1b with acetic acid gave 7 in an SN2‐type ring opening at C3, followed by an O→N acyl shift. Treatment of enantiopure (+ )‐(2S,3R)‐1b with benzenethiol, indole and acetic acid gave the corresponding enantiomerically pure β‐functionalized α‐amino acid derivatives. Functionalization of 1b at nitrogen strongly increased the reactivity: N‐acylaziridine 8 isomerized to trans‐oxazoline 11 when treated with boron trifluoride etherate in acetonitrile.
Conversion of aziridine‐2‐carboxylic esters into 2H‐azirine‐2‐carboxylic esters
Authors: Legters Johan , Thijs Lambertus , Zwanenburg Binne
Published: September 2010

Aziridine‐2‐carboxylic esters 1 were converted into 2H‐azirine‐2‐carboxylic esters 4 in two steps. Treatment of 1 with tert‐butyl hypochlorite in ether gave smooth N‐chlorination. Reaction of N‐chloroaziridines 2 with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) or 1,4‐diazabicyclo[2.2.2]‐octane (DABCO) gave 2H‐azirine‐2‐carboxylic esters 4 in moderate yields, with concomitant formation of aziridines 1. Aziridines 1 could readily be N‐brominated with N‐bromosuccinimide. Treatment of N‐bromoaziridines 3 with base, however, did not lead to azirine formation. N‐Halogenated aziridines 2 and 3 exist as mixtures of invertomers, which slowly interconvert in solution.
Synthesis and spectroscopic characterization of the doubly locked 9E,11Z retinal model systems 7E,13E‐11,19–10,20‐dimethanoretinal and its 13Z isomer
Authors: Groesbeek M. , Robijn G. W. , Lugtenburg J.
Published: September 2010

7E,13E‐11,19‐10,20‐dimethanoretinal (1) and its 13Z isomer 2 were prepared from β‐ionone, using the novel synthon 2‐(diethoxyphosphinyl)‐5,5‐dimethoxyhexanenitrile. This synthon was also used to prepare 7E,9E,13E‐10,20‐methanoretinal (3) and its 13Z isomer 4 in high yield, starting from β‐ionone. Spectroscopic analysis (mass, 1H and 13C NMR and UV/Vis) of these compounds is discussed. The introduction of the methano bridges leads to minimal steric and electronic changes. The photostationary state reached from 1 and 2 has the 13Z form 2 as the main constituent. This is one of the very few with a Z form as the main constituent of the photostationary state. 1 and 2 are very sensitive to acid‐catalyzed isomerization of the 13‐C14‐C double bond. The presence of the 11,19‐methano bridge is responsible for this efficient Z‐E isomerization.
Towards a rational design of resolving agents. Part IV. Crystal packing analyses and molecular mechanics calculations for five pairs of diastereomeric salts of ephedrine and a cyclic phosphoric acid
Authors: Leusen Frank J. J. , Slot Hubert J. Bruins , Noordik Jan H. , van der Haest Albertus D. , Wynberg Hans , Bruggink Alle
Published: September 2010

Detailed structural studies of five pairs of diastereomeric salts of ephedrine and halogen‐substituted chiral cyclic phosphoric acids indicate a correlation between the efficiency of the resolution process and the lattice energy difference between the salts of a diastereomeric pair. Attempts to model such a correlation quantitatively by lattice energy calculations with Molecular Mechanics (MM) methods have not yet been successful. The MM techniques proved unable to reproduce the crystal structures with sufficient accuracy. However, the results of the analyses qualitatively support the presumed correlation, and show that the five resolutions are directed by different acid‐base interactions in the hydrophobic layers.
Synthesis of 5β‐alkylthebaines, 5β‐alkyl‐10α‐ethylthebaines and 5β,10α, 10β‐triethylthebaine; Diels‐Alder reactions to 5β‐alkyl‐ and 5β‐alkyl‐10α‐ethyl‐6α, 14α‐ethenoisomorphinans (chemistry of opium alkaloids, Part XXXVI
Authors: Woudenberg R. H. , Oosterhoff B. E. , Lie T. S. , Maat L.
Published: September 2010

5β‐Ethylthebaine (3), together with 5β‐butylthebaine (4), was obtained from thebaine (1) after reaction with butyllithium and ethyl iodide. With butyllithium and diethyl sulfate, thebaine yielded 5β‐ethylthebaine (3), 5β, 10α‐diethylthebaine (5), and 5β, 10α, 10β‐triethylthebaine (6). The ratio of the compounds (3:4 and 3:5:6) depended on the excess of reagents used. Employing the reversed sequence of addition of reagents, that is, first diethyl sulfate and then butyllithium, we prepared 5β, 10α‐diethylthebaine (5) and 5β‐methyl‐10α‐ethylthebaine (8) from 5β‐ethylthebaine (3) and 5β‐methylthebaine (7), respectively. These alkylation reactions are discussed in terms of Pearson's hard‐soft acid‐base theory.

Diels‐Alder reaction of 3, 5 and 8 with ethyl acrylate gave exclusively 7α‐substituted 6α, 14α‐ethenoisomorphinans 9, 10 and 11, respectively. Esters of the cycloadducts 9 and 11 were converted into their tertiary alcohols 12 and 13 with methylmagnesium bromide. The 3‐methoxy group in 12 and 13 was hydrolyzed with a solution of potassium hydroxide in 1,2‐ethanediol to give phenols 14 and 15.
Dual behaviour of sepiolites as single electron acceptors or Lewis acids: Reactivity of two α‐acetoxystyrenes adsorbed on a iron(III)‐exchanged sepiolite
Authors: Baldoví Vicenta , Corma Avelino , García Hermenegildo , Iborra Sara , Miranda Miguel A. , Primo Jaime
Published: September 2010

Iron(III)‐exchanged sepiolites exhibit dual behaviour as catalysts in the reactions of α‐acetoxystyrenes 1a,b; operating as Lewis acids (to give 2–5) in thermolysis reactions under reduced pressure or as single‐electron acceptors (to give 7) in photolysis under aerobic conditions.
Palladium‐catalyzed allylation of α‐hydroxy acids
Authors: Moorlag Henk , de Vries Johannes G. , Kaptein Bernard , Schoemaker Hans E. , Kamphuis Johan , Kellogg Richard M.
Published: September 2010

Mandelic and lactic acids are converted to the 1,3‐dioxolan‐4‐ones by treatment with acetone dimethyl acetal. Deprotonation followed by treatment with an allyl acetate and a catalytic amount (1 mol %) of palladium catalyst afforded the allylated dioxolanones, which could be hydrolyzed to the corresponding α‐allyl α‐hydroxy acids. The lithium enolate of the dioxolanone of mandelic acid was also coupled with methallyl, cinnamyl, geranyl and (E)‐1‐methyl‐2‐butenyl acetates. The zinc enolate of the dioxolanone of lactic acid reacted smoothly with allyl acetate in a catalyzed reaction whereas no detectable reaction was observed when the lithium enolate was used. This appears to be the result of complications arising from the enhanced basicity of the lithium compared to zinc enolate.

Various attempts were made to achieve enantioselectivity using chiral ligands on the palladium catalyst. The zinc enolates were found to provide better results although the enantioselectivity was only modest, about 30% enantiomeric excess being the best result obtained. Chiraphos proved to be the best optically active ligand of a variety tested.