bluuebunny/crossref_metadata_2025_split huggingface dataset:
The coordination chemistry of optically active ligands. Copper(II) and nickel(II) compounds containing (S)‐(+)‐1‐amino‐2‐propanol as a ligand
Authors: Nieuwpoort G. , Reedijk J. 
Published: September 2010

AbstractCopper(II) and nickel(II) compounds with (S)‐(+)‐1‐amino‐2‐propanol (S‐ap) are described and compared with the corresponding compounds containing racemic 1‐amino‐2‐propanol ((RS)‐ap) previously reported. Both ligands give analogous coordination compounds, except in the case of the chlorides of formula MCl2(ap)2, which are only obtained with (RS)‐ap. Similar differences were found in solution using conductometric titrations. Infrared and ligand field spectra for the racemic and optically active compounds are almost identical. Circular dichroism spectra show that Λ(δδδ) is the most stable configuration for the tris‐chelates. For the bis‐compounds the ligands could be assigned to cis‐ or trans‐positions by comparing the rotational strength of the d‐d transitions. In addition, the different melting points of the isomers are related to their different geometries. The comparison further indicates that in compounds with monodentate coordinating ap ligands steric hindrance is less important in the case of the compounds containing S‐ap.
Chelation of cis‐Pt(NH3)2Cl2 by the deoxynucleotide d(CCGG)
Authors: Marcelis A. T. M. , Canters G. W. , Reedijk J. 
Published: September 2010

AbstractThe main product of the reaction between cis‐Pt(NH3)2Cl2 and the deoxytetranucleotide d(C‐C‐G‐G) was isolated. A 1H NMR study shows that the two guanosine bases are chelating to cis‐Pt(NH3)2 via their N(7) atoms.
Chemistry of crown ethers. XVII. Triphase catalysis by immobilized benzo‐18‐crown‐6
Authors: van Zon A. , de Jong F. , Onwezen Y. 
Published: September 2010

AbstractSeveral immobilized benzo‐18‐crown‐6 derivatives have been synthesized and a study has been made of their activities as triphase catalysts in the reaction between 1‐bromooctane in toluene and aqueous potassium cyanide. In each case the reaction rate was proportional to the 1‐bromooctane concentration and to the amount of catalyst and also depended on the potassium cyanide concentration. Under non‐stirred conditions the activity per crown ether moiety was dependent on the degree of functionalization of the supporting polymer, being high for a highly substituted polystyrene/divinylbenzene resin and low for a sparingly substituted one. The beneficial effect of the high loading disappeared completely, however, under stirred conditions. The triphase catalyst can be used both with liquid‐liquid‐solid and with solid‐solid‐liquid systems and can be recovered without significant loss of activity.
Structure analysis of (+)‐1,3,4,14b‐tetrahydro‐2‐methyl‐2H‐dibenzo[b,f]pyrazino[1,2‐d][1,4]oxazepine monohydrobromide, a potential anti‐depressant
Authors: van Rij‐Oskam J. J. , van Egmond A. B. , Feil D. , Zeelen F. J. 
Published: September 2010

AbstractThe crystal structure and absolute configuration of the title compound were determined and compared with those of (+)‐1,2,3,4,10,14b‐hexahydro‐2‐methyldibenzo[c,f]pyrazino[1,2‐a]‐azepine monohydrobromide (mianserin hydrobromide), a related tetracyclic compound.
Stereoselective synthesis of the imidazole alkaloids (+)‐pilocarpine and (+)‐isopilocarpine. (Imidazole chemistry, Part IX)
Authors: Noordam A. , Maat L. , Beyerman H. C. 
Published: September 2010

AbstractA novel synthesis of (+)‐pilocarpine (10a) is described. L‐Histidine is converted into methyl (R)‐2‐bromo‐3‐(l‐methyl‐5‐imidazolyl)propionate (5) in which the configuration has been inverted. Alkylation of dibenzyl ethylmalonate with 5 yields the imidazole compound 6, again with inversion. Finally, 6 is converted into a mixture of (+)‐pilocarpine (10a) and (+)‐isopilocarpine (10b), the separation of which is well established.
Chemistry of crown ethers XVIII. Isolation and purification of 18‐crown‐6 by selective complexation with non‐ionic compounds
Authors: van Zon A. , de Jong F. , Reinhoudt D. N. , Torny G. J. , Onwezen Y. 
Published: September 2010

AbstractA number of non‐ionic compounds have been found to form solid complexes with 18‐crown‐6. The highest efficiencies of isolation and the highest selectivities were obtained with nitromethane, dimethyl carbonate and dimethyl oxalate. The usefulness of these compounds was demonstrated in the isolation of >98% pure 18‐crown‐6 from crude reaction mixtures.
Proton acid induced rearrangements of bicyclo[2.2.0]hexene carboxylic acids and esters
Authors: van Rantwijk F. , van der Stoel R. E. , van Bekkum H. 
Published: September 2010

AbstractBicyclo[2.2.0]hex‐5‐ene‐2‐endo‐carboxylic acids and their methyl esters give the corresponding γ‐lactones, together with isomerized products, upon treatment with hydrochloric acid in acetic acid. The reaction mechanism is discussed.
Photochemical reactions of quinoid α‐aryl‐substituted γ‐oxo‐α,β‐unsaturated carboxylic esters and amides. Formation of naphthacene and cycloheptatriene derivatives
Authors: Verboom W. , Brants J. J. M. , Bos H. J. T. 
Published: September 2010

AbstractIrradiation of the quinoid α‐aryl‐substituted γ‐oxo‐α,β‐unsaturated carboxylic esters 7a‐b and amides 10a‐b, derived from 9,10‐phenanthrenequinone, afforded, in addition to the Z/E isomers, the 8‐oxo‐8H‐benzo[f,g]naphthacene‐9‐carboxylic esters (13a‐b) and amides (15a‐b), respectively, by a dehydro‐cyclization of the stilbene system. Starting from the carboxylic ester 7c and amide 10d, with blocked ortho positions, cycloisomerization via an intramolecular (4 + 2)‐cycloaddition, with formation of the cycloheptatriene derivatives 16 and 17, was observed.Irradiation of the α‐aryl‐substituted γ‐oxo‐α,β‐unsaturated carboxamides 12, derived from 3,5‐ditert‐butyl‐o‐benzoquinone, afforded, in addition to the Z/E isomers, the corresponding cycloheptatriene‐carboxamides 18. Starting from the carboxamide 12b,Φ = 0.074 ± 0.006 for the Z → E isomerization,Φ= 0.039 ± 0.004 for the E → Z isomerization and for the cycloisomerization Φ= 0.0016 ± 0.0006.
Reactions of low‐valent titanium with various functional groups (phenyl derivatives)
Authors: Dams Rudy , Malinowski Marek , Geise Herman J. 
Published: September 2010

AbstractTitanium slurries, prepared by reduction of titanium chlorides with LiAlH4, are not only effective in couplings of ketones and aldehydes to alkenes, but also in reductive couplings and reductions of other functional groups.
Semi‐empirical calculations concerning the geometry of the cycloheptatrienyl anion
Authors: Zwaard A. W. , Brouwer A. M. , Mulder J. J. C. 
Published: September 2010

AbstractSemi‐empirical calculations (mostly MINDO/3) have been performed on singlet C7H7−. A preference for planar structures is evident from the calculations. Two different structures (an allylic structure and a pentadienylic structure, respectively) are found as absolute minima on the potential surface. They were found to be second‐order Jahn‐Teller deformations of the highly symmetrical (D7h) structure, the energy lowering on these distortions being about 9 kcal/mole. A first‐order Jahn‐Teller effect was found to be negligible. The related C5H5+ system is considered briefly for comparison.
Synthesis of 1‐alkoxy‐3‐buten‐1‐ynes and some homologues
Authors: van Rijn P. E. , Everhardus R. H. , Brandsma L. 
Published: September 2010

Abstract1‐Alkoxy‐3‐buten‐1‐ynes and the homologues ROCC‐CHCR′R″ (R′ and R″  H or alkyl, or R′R″  [CH2]5) have been obtained in satisfactory yields from allenic bis‐ethers RO‐CHCCH‐C(R′)(R″)OR and ethyllithium in diethyl ether. With excess ethyllithium, the enynes C2H5‐CC‐CHCR′R″ (R′  alkyl, R″  alkyl or H or R′R″  [CH2]5) were formed.
A MINDO/3 exploration of some (CH)2+8 structures
Authors: Klumpp Gerhard W. , Fleischhauer Jörg , Schleker Wolfgang 
Published: September 2010

AbstractWithin the context of a study aimed at a possible delocalized structure (IVb) of the cubane dication energies, charges and geometries have been calculated for three known and for four unknown types of dications derived from the (CH)82+ family.
Conformational analysis of an RNA triplet in aqueous solution: m62A‐U‐m62A studied by two‐dimensional nuclear magnetic resonance at 500 MHz
Authors: Lankhorst Peter P. , Groeneveld Cornelis M. , Wille Gerry , van Boom Jacques H. , Altona Cornelis , Haasnoot Cornelis A. G. 
Published: September 2010

AbstractThe complete assignment of the 18 ribose proton NMR signals of the trinucleoside diphosphate m62A(1)‐U(2)‐m62A(3) is given. The analysis was carried out by means of spin‐echo‐correlated spectroscopy and two‐dimensional J‐resolved spectroscopy at 500 MHz. Analysis of the chemical shifts and coupling constants demonstrates that the trimer does not form a classical right‐handed helix. Instead, the interior U(2) fragment appears to be “bulged‐out”, concomitant with a next‐nearest‐neighbour interaction between the terminal purine bases. An analogy with the behaviour of the first three residues in the tetramer m62A(1)‐U(2)‐m62A(3)‐U(4) is noted. An analysis of the coupling constants in terms of the N/S equilibrium and population distribution around the torsional degrees of freedom along the sugar‐phosphate backbone is presented.
Synthesis and reactivity of 22,23‐methylene‐2,3,17,18‐tetramethyl‐23‐hydro‐1, 19‐[21H,24H]‐bilindion‐10‐enium trifluoroacetate
Authors: de Groot J. A. , van der Steen R. , Lugtenburg J. 
Published: September 2010

AbstractThe biliverdinium salt 1 has been prepared in high yield and its behaviour towards nucleophiles studied. The reactions have been found to occur selectively on the central carbon atom 10 and to lead to bilirubin systems. In addition, the photoisomerisation of the bilirubin model compound 5, prepared from 1, has been investigated.
Effect of pressure on the (2 + 2) cycloaddition of cyclopropanone diethyl acetal to tetracyanoethylene
Authors: Wiering Petrus G. , Steinberg Herbert 
Published: September 2010

AbstractThe pressure dependence of the (2 + 2) cycloaddition of cyclopropanone diethyl acetal to tetracyanoethylene in methylene chloride and acetonitrile has been studied. The reaction is about ten times faster in the less polar methylene chloride in the pressure range 1‐2000 atm. The volume of activation is found to be ‐20.9 cm3/mole (CH2Cl2) and ‐24.5 cm3/mole (CH3CN). The estimated volume of the transition state is equal in both solvents and is of the same order of magnitude as the partial molar volume of the cycloadduct 1,1‐diethoxy‐2,2,3,3‐tetracyanocyclopentane. These findings are in agreement with a concerted cycloaddition mechanism via a weak complex of the reactants.
Photochemical, transformations of tetracyclo [3. 3.0.02,4.03,6]OCT‐7‐ene
Authors: Stapersma J. , Klumpp G. W. 
Published: September 2010

AbstractCyclooctatetraene is a common product of photolysis of the title compound la. Depending on reaction conditions it is accompanied by benzene (solvent: cyclohexane, γ = 253.7 nm), benzene plus semibullvalene (acetone, 300 nm), and an oxetane (cyclohexane, 350 nm, presence of an equimolar amount of benzophenone).
An approach to the synthesis of [2]benzopyrano[3,4‐c]pyrroles; alternative dopaminergic molecules
Authors: Loozen H. J. J. , Brands F. T. L. , de Winter M. S. 
Published: September 2010

AbstractBenzyloxy‐substituted [2]benzopyrano[3,4‐c]pyrroles have been prepared by thermolysis of suitably substituted benzocyclobutenes, via an intramolecular Diels‐Alder reaction of the quinodimethane intermediate with an aldehyde function.Upon thermolysis of 3,4‐bis(benzyloxy)‐7‐[[(methoxycarbonyl)(2‐oxoethyl) amino]methyl]bicyclo‐[4.2.0]octa‐l,3,5‐triene (12), in refluxing bromobenzene,tras‐7,8‐bis(benzyloxy)‐2‐(methoxy‐carbonyl)‐l,2,3,3a,5,9b‐hexahydro[2]benzopyrano[3,4‐c]pyrrole (13) was isolated. Upon thermolysis of N‐alkyl‐N‐(2‐oxoethyl)bicyclo[4.2.0]octa‐l,3,5‐triene‐7‐carboxamides (such as 19, 29a‐d and 33a,b) in bromobenzene,trans/cismixtures of N‐substituted‐3,3a,5,9b,tetrahydro‐2H‐[2]‐benzopyrano‐[3,4‐c]pyrrol‐1‐ones were obtained in yields of 70 to 85%. In this way, 20, 21, 30a‐d, 31a‐d, 34a,b and 35a,b have been obtained. As starting materials, suitably substituted benzocyclo‐butenecarboxylic acids were used (7, 46 and 54). These compounds were converted into the acid chlorides and condensed with substituted 2‐(hydroxyethyl)amines to afford the N‐alkyl‐N‐(2‐hydroxyethyl)benzobicyclo[4.2.0]octa‐l,3,5‐triene‐7‐carboxamides 27, 28a‐d and 32a,b, which were then oxidized to the required N‐(2‐oxoethyl) derivatives by means of DMSO‐oxalyl chloride complex.Reduction of the tetrahydro‐2H‐[2]benzopyrano[3,4‐c]pyrrol‐1‐ones 20, 21, 30b, 30c and 35b with borane‐dimethyl sulfide complex or with LiAlH4‐AlCl3complex gave the hexahydro[2]benzo‐pyrano[3,4‐c]pyrroles 22, 23, 36, 37 and 38. Subsequently, these compounds were converted into catecholamines 24, 25, 39, 40 and 41 by catalytic reduction.
Aromatic sulfonation 84. Sulfonation of bi‐ and tri‐phenylene
Authors: Cerfontain Hans , Laali Khosrow , Lambrechts Hans J. A. 
Published: September 2010

AbstractThe mono‐ and di‐sulfonation of biphenylene (1) and triphenylene (2) with SO3 in nitromethane as solvent at 0°C has been studied. The monosulfonation of both 1 and 2 leads exclusively to the formation of the 2‐sulfonic acid. In the case of 1, this results from the lower cation localization energy of the 2‐ as compared with the 1‐substitution; with 2, the substitution at the 1‐position is prevented by large steric hindrance. The sulfonation of biphenylene‐2‐sulfonic acid yields 65 % 2,6‐ and 35 % 2,7‐disulfonic acid, while that of triphenylene‐2‐sulfonic acid yields 59% 2,6‐, 1% 2,7‐ and 40% 2,11‐disulfonic acid. For both bi‐ and tri‐phenylene‐2‐sulfonic acid, the reactivity order of the sterically accessible positions in the non‐sulfo‐containing rings is governed by the (electronic) directing effect of the 2‐SO3H substituent.
The use of immobilized enzymes in organic synthesis. Part 6. Oxidation of 1‐alkyl‐3‐carbamoylpyridinium chlorides by rabbit liver aldehyde oxidase
Authors: Angelino S. A. G. F. , Buurman D. J. , van der Plas H. C. , Müller F. 
Published: September 2010

AbstractA method is described for the oxidation of some 1‐alkyl‐3‐carbamoylpyridinium chlorides by reaction with immobilized rabbit liver aldehyde oxidase. With the 1‐methyl‐, 1‐ethyl‐and 1‐n‐propyl derivatives, only the 1‐alkyl‐1,6‐dihydro‐6‐oxo‐3‐pyridinecarboxamides have been obtained, but with the t‐Bu analogue the corresponding 4‐oxo compound was found as single product. The i‐Pr derivative gave rise to a mixture of the corresponding 4‐ and 6‐oxo compounds. From the kinetic data some information has been acquired with respect to the enzyme active‐site environment and the binding of the substrates to the enzyme.
A method for the determination of pyrite in coal
Authors: Kos C. H. 
Published: September 2010

AbstractA rapid and simple method for the determination of pyrite in coal, based upon a two‐step extraction of iron from coal is presented. After milling the coal in a tungsten‐carbide vessel, the non‐pyritic iron is first removed and then the pyritic iron dissolved. This is then followed by AAS analysis. Analysis of pyritic sulfur and total iron in four types of coal demonstrate the reliability of this method.
Synthesis of DNA on a solid support by the hydroxybenzotriazole phosphotriester approach
Authors: Marugg J. E. , van der Morel G. A. , de Vroom E. , Bosch D. , van Boom J. H. 
Published: September 2010

AbstractApplication of the phosphorylating agent 2‐chlorophenyl‐0,0‐bis(1‐hydroxybenzotriazolyl)‐phosphate enabled us to synthesize DNA fragments (e.g., d‐AGGATCCT and d‐GTTCGG) on a polystyrene solid support:
On the luminescence of lanthanide decatungstates. III. Tetrabutylammonium and brucinium salts
Authors: Blasse G. , Zonnevijlle F. 
Published: September 2010

AbstractThe luminescence properties of the following decatungstates have been investigated: X9LnW10O36 (X = tetra‐n‐butylammonium or brucinium; Ln = Sm, Eu, Dy). Due to the large X ions, the separation between the lanthanide ions is very large. Consequently no interaction between these ions occurs, not even in the case of Sm and Dy. The tetra‐n‐butylammonium salts contain a small number of alkali metal ions. The emission of Eu3+ has been used to analyse the composition in more detail. The brucinium salts do not luminesce efficiently upon tungstate excitation, since the excitation energy is lost, for the greater part, in the brucinium ions.
Synthesis and structure of 6‐exo‐hydroxy‐1,2‐diphenyl‐1‐phosphoniatricyclo [3.3.1.1]decane iodide, a derivative of 1‐phosphaadamantane
Authors: Meeuwissen H. J. , Sirks G. , Bickelhaupt F. , Stam C. H. , Spek A. L. 
Published: September 2010

AbstractThe annelation reaction between l,2,3,6‐tetrahydro‐1‐phenyl‐4‐(1‐pyrrolidinyl)phosphorin 1‐oxide (10) and 2,2‐bis(chloromethyl)acetophenone (7) leads to two stereoisomeric 7‐benzoyl‐3‐phenyl‐3‐phosphabicyclo[3.3.1]nonan‐9‐one 3‐oxides 11a and 11b. Their difference resides in the configuration at phosphorus, which also determines the conformation of the bicyclononane skeleton, as revealed from the crystal structures. Reduction of the two keto functions in 11a with NaBH4 to give 12a, followed by HSiCl3 reduction to the phosphine 13a and acid‐catalyzed ring closure, yields the title compound (4a), the structure of which was corroborated by an X‐ray crystal structure determination. Interestingly, the same sequence of reactions converts 11b into a 3.3 : 1 mixture of 4a and 4b; presumably, inversion of configuration at phosphorus occurs in the last step and is catalyzed by acid.
The conversion of primary amines into nitrones: An extension of the Kröhnke reaction
Authors: Katritzky Alan R. , Dabbas Nadira , Patel Ranjan C. , Cozens Andrew J. 
Published: September 2010

AbstractPrimary amines react with 2‐(ethoxycarbonyl)‐4,6‐diphenylpyryliums to form pyridiniums. These are hydrolysed to 2‐carboxylatopyridiniums which react with p‐nitroso‐N,N‐dimethylaniline to give nitrones.
Réactivité comparée de germyléneamines, de digermylamines et de cyclogermazanes vis à vis de nitrones et d'oxaziridines isomères
Authors: Ère‐Baudet Monique Rivi , Rivière Pierre , Castel Annie , Lacrampe Georges , Satgé Jacques 
Published: September 2010

AbstractL′addition de nitrones (R2C=NR′O) dans la liaison Ge‐N de germylamines acycliques (R3Ge)2NR′ conduit à des dérivés d'insertion dont la stabilité est discutée.Les nitrones réagissent sur les germylèneamines (R2Ge=NR′) par cycloaddition dipolaire 1‐3 conduisant à des 1,3,5,2‐oxadiazagermolidines thermiquement instables. La décomposition de ces nouveaux hétérocycles conduit à l'imine carbonée correspondant à la germylèneamine de départ, au germoxane via la germanone transitoire et au nitrène correspondant à la nitrone.La 2‐t‐butyl‐3‐phényloxaziridine conduit aux mêmes types de dérivés par ouverture de la liaison C‐O de cet hétérocycle.Les réactions des cyclogermazanes sur les nitrones ne commencent qu'aux environs de 120°C et conduisent à des résultats semblables à ceux obtenus avec les germylèneamines. Il est montré qu'en présence de nucléophiles (Et3N, HMPT), ces réactions se produisent dès 70°C. Les nucléophiles semblent agir comme catalyseurs de dépolymérisation des cyclodigermazanes en germylèneamines.Les mécanismes de formation et de décomposition des 1,3,5,2‐oxadiazagermolidines sont discutès.La cycloaddition 1‐3 sur les nitrones apparaît comme une réaction de caractérisation chimique des germylèneamines.
Photochemical reactions of some aromatic thiones with bis(methylthio)ethyne; (4 + 2)‐ versus (2 + 2)‐cycloaddition products. Spectroscopic evidence for the equilibrium thiete ⇄ α,β‐unsaturated dithioester
Authors: Brouwer A. C. , Bos H. J. T. 
Published: September 2010

AbstractIrradiation (λ > 525 nm) of the aromatic thiones 2 in the presence of bis(methylthio)‐ethyne 3 causes two cycloaddition reactions to occur between the photochemically excited thione 2 and the acetylene 3, as concluded from the isolated products. Compounds with structure 6 are believed to be products of a (4 + 2)‐cycloaddition reaction, whereas the formation of the isolated α,β‐unsaturated dithio esters 4 is rationalised on the basis of a (2 + 2)‐cycloaddition reaction. The preference for one reaction pathway over the other depends on the thione used and is discussed in terms of the structure of the thione 2. Spectroscopic observation of the equilibrium thiete 5 ⇄ α,β‐unsaturated dithio ester 4, in solution provides direct evidence for the (2 + 2)‐photocycloadducts, thietes 5.
The mean bond dissociation energy of the carbonmagnesium bond in bis(2,2‐dimethylpropyl)magnesium
Authors: Akkerman O. S. , Schat G. , Evers E. A. I. M. , Bickelhaupt F. 
Published: September 2010

AbstractThe standard enthalpy of formation of solid bis(2,2‐dimethylpropyl)magnesium (dineopentylmagnesium, Np2Mg) has been determined from its reaction enthalpy with aqueous hydrobromic acid and found to be ‐235.8 ± 5.5 kJ·mol−1. Using the experimentally determined sublimation enthalpy of Np2Mg and the enthalpies of formation of the 2,2‐dimethylpropyl radical and gaseous magnesium, the mean dissociation energy of the carbonmagnesium bond in the monomeric title compound is found to be 133.7 ± 5.0 kJ·mol−1. This value is discussed and compared with those of other reported carbonmagnesium bonds. In combination with the previously determined difference in enthalpy of formation of dimeric and monomeric Np2Mg, the bond energy of the bridging 2,2‐dimethylpropylmagnesium bonds in dimeric Np2Mg is calculated to be D̄B = 205 ± 3 kJ·mol−1, which is a remarkably high value.
Chemistry of ketene acetals VI. The influence of the dicyanoethene moiety on the reactivity and selectivity of β,β‐dicyano‐α,β‐unsaturated ketones in cycloadditions with ketene acetals
Authors: Bakker C. G. , Ooms P. H. M. , Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

AbstractThe (2 + 2) versus (4 + 2) cycloadditions of two ketene acetals R1R2C=C(OMe)2 (R1 = R2 =OMe, 1a; R1 = H, R2 = Me, 1b) with several β, β‐dicyano‐α, β‐unsaturated ketones R3CO‐R4C=C(CN)2 (2a‐e, Table I) have been investigated. Cyclobutanes 3 were only obtained at room temperature in the cycloaddition of 2a (R3 = R4 = Ph) with 1b and 2d (R3, R4 = naphthyl) with 1a or 1b. In the latter case, an oxetane was obtained when ZnCl2 was used as a catalyst.The thermodynamically more stable (4 + 2) cycloadducts were obtained at higher temperatures, except from 2e, in which the carbonyl group is part of an amide function. A high regiospecificity has been found in these cycloadditions. The influence of the dicyanoethene moiety on the cycloadditions is discussed and compared to analogous cycloadditions of 1a and 1b with α,β‐unsaturated ketones and α‐diketones.
Photochemistry of α,α,ω,ω‐tetramethyl‐1,2‐cycloalkanediones; influence of the conformation of the diketo moiety on the photochemical behaviour
Authors: Verheijdt Paul L. , Cerfontain Hans 
Published: September 2010

AbstractA series of α,α,ω,ω‐tetramethyl‐1,2‐cycloalkanediones, with a ring size varying between 4 and 8 C atoms (la‐e), together with 2,2,5,5‐tetramethyl‐3,4‐hexanedione (2a), have been irradiated both in 2‐propanol and in benzene in order to study the influence of the diketo conformation on the photochemical behaviour of 1,2‐diketones. Irradiation of lb‐d in 2‐propanol leads exclusively to photoreduction with formation of the corresponding acyloins via intermolecular H abstraction, whereas le and 2 yield predominantly the 2‐hydroxycyclobutanone product via intramolecular H abstraction. The irradiations of la‐e in benzene lead to different products for the six homologous cyclic 1,2‐diketones. Mechanisms for the formation of the various products are proposed. It is concluded that the 1,2‐diketones with Φ (ground state) <90° and >90° react, upon excitation, from a conformation having a planar cisoid and transoid diketo geometry, respectively.