Use of oxo-metallic derivatives in isomerisation: Reactions of unsaturated alcohols

The isomerisation of α-acetylenic alcohols to ethylenic carbonyl derivatives and the isomerisation of α-ethylenic alcohols to the corresponding allyl alcohols may be effected in good yields in a single step using oxometallic derivatives. The vanadate esters are particularly efficient. Mechanistic explanations are given.     

Selective reductive dimerization of homocubane series oximes

The mixture of di- and monoethylene ketals obtained by the reaction of 1,9-dibromopentacyc lo[5.4.0.0^2,6.0^3,10.0^5,9]-undeca-8,11-dione followed by hydrolysis and ring contraction by Faworsky method was converted into a mixture of ethylene ketals of 7-bromopentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decan-6-one-4- and 5-bromopentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decan-6-one-8-carboxylic acid where the carboxy group was replaced by bromine along the procedure of Hunsdiecker-Borodine-Cristol. 6-Ethylene ketal of the pentacyclo[5.3.0.0^2,5.0^3,9.0^4,8] decan-6-one obtained by the debromination of ethylene ketals of 4,7- and 5,8-dibromopentacyclo[5.3.0.0^2,5.0^3,9.0^4,8] decan-6-one was hydrolyzed to ketone whose oxime was selectively reduced on a platinum catalyst into the di-6-pentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decylamine. The reaction of reductive dimerization was also characteristic of pentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]-nonan-9-one and pentacyclo[6.3.0.0^2,6.0^3,10.0^5,9]undecan-4-one oximes, whereas the composition of the reduction products of pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecan-8-one oxime depended on the amount of the catalyst.     

On isomerisation of nitroparaffins

The investigation deals with the isomerisation of primary nitroparaffins into hydroxamic acids under influence of acetic anhydride or ketene, in presence of basic catalysts.

A practical application of the hydrolysis of 1:2-dinitroethane to hydroxylamine sulphate is described.

Another application is the preparation of caprolactam by the reaction of cyclohexanone with 1:2-dinitroethane in presence of concentrated sulphuric acid.     

Asymmetric base-mediated epoxide isomerisation

The base-mediated rearrangement of epoxides into allylic alcohols is a well-known synthetic transformation. The first enantioselective version of the reaction using a chiral base was reported in 1980. Since then, the reaction has received a lot of attention mostly due to the great usefulness of chiral allylic alcohols in organic synthesis. Major breakthroughs in the area were the first report on using a sub-stoichiometric amount of chiral base, and the development of chiral bases for a true catalytic reaction protocol. The present review covers the time from when the first asymmetric epoxide isomerisation reaction was reported (1980) up to now, focusing on the period 1997-2001.     

Optimisation of photo-induced geometric isomerisation of azobenzene derivatives in dye-doped polymer films for enhanced photo-induced poling

Photo-induced geometric isomerisation of azobenzene based chromophores can be utilised in a variety of molecular control procedures including photo-induced poling. In such processes additional mobility is imparted to chromophores trapped in a glassy matrix through the photo-induced trans-cis-trans cycle. We show that by using selected narrow wavelength bands of light to induce the isomerisation cycle during photo-induced poling, enhanced levels of polar order can be obtained in comparison to those obtained with monochromatic light. We attribute this to an increase in the fraction of chromophores which undergo isomerisation via an inversion mechanism. As a result, a higher proportion of the chromophores are able to participate in the photo-induced poling process since the free volume for isomerisation is reduced from that required for the rotation mechanism.     

A biocatalytic redox isomerisation

A bi-enzymatic cascade for the redox-isomerisation of allylic alcohol is presented. Coupling of an alcohol dehydrogenase to an enoate reductase has been successfully applied in one pot for the isomerisation of an allylic alcohol to the corresponding ketone. Critical parameters for yield and selectivity have been investigated.     

An example of the base induced isomerisation of the epoxide ring in enolizable epoxyketones: isomerisation of 8,9-epoxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-one and some of its derivatives

The title compounds in the basic medium (RO^?/ROH) afford an unique example of competition between isomerisation via the enolate anion and epoxide-ketone isomerisation.     

The kinetics of the E-Z-E isomerisation and liquid-crystalline properties of selected azobenzene derivatives investigated by the prism of the ester group inversion

Two new groups of azobenzene ester derivatives were synthesised: alkyl 4-[4-(nonyloxy)phenyl]diazenyl]benzoates and 4-[4-(nonyloxy)phenyl]diazenyl]phenyl alkanoates. All 35 presented homologues are mesogenic. Moreover, some of the above-mentioned compounds exhibit rich liquid-crystalline polymorphism likewise tetramorphism. During this investigation by the use of polarising optical microscopy, differential scanning calorimetry and X-Ray studies, six types of mesophases were detected: nematic, smectics (A, C, I, F) and G. Furthermore, due to the presence of the photosensitive azo moiety, the E–Z isomerisation reaction is possible. This process, which is initiated by the UV irradiation, causes significant changes in the UV-Vis absorption spectra of investigated compounds. However, the photoisomerisation is a reversible process and in the dark the thermal relaxation of Z isomer takes place. Based on the achieved data, the kinetic constants of the isomerisation and relaxation processes were calculated. It shows that conversion of the ester bond makes some changes in the optical properties. The shift of about 7 nm of the absorbance maximum was observed. Surprisingly, the inversion of the ester group has significant influence on the liquid-crystalline polymorphism replacing one mesophase (for benzoates) into four (for alkanoates).     

邻硝基乙酰苯胺衍生物的XPS振起伴峰及其价带谱的研究

研究了一组邻硝基乙酰苯胺衍生物的X射线光电子能谱(XPS).观察到硝基的N1s光电子谱有明显分裂,可认为是N1s振起伴峰的反映,而且苯环上的取代基对该振起伴峰强度有影响,按照Pignataro等关于振起伴峰与主峰的能量分离以及分子内电荷转移有关的观点,计算了振起伴峰与主峰的面积比.结果表明,峰间距与面积比的趋势一致.因此二者都可作为分子内电荷转移的粗略估计.     

Kinetics of the reactions of cyclopropane derivatives. IV. Kinetic isotope effect in the isomerisation of cyclopropylamine

The high-pressure isotopic rate ratio k_H/k_D for isomerisation of cyclopropylamine and cyclopropylamine-N-d₂ is 1.06 at 649–678 K, supporting a mechanism which does not involve migration of hydrogen from the amine group in the rate-determining step.     

Order and structure of the outer valence MO'S of some derivatives of pentafluorobenzene

Conclusions According to the data from the photoelectron spectra and the MNDO calculations, the orbitals of the functional group and the upper -orbitals of the ring in the compounds C₆F₅X with X=NCO and N₃ interact; however, their interaction is less effective than the interaction in the molecules of the hydrocarbon analogs; when X=NO₂, NO, CHO, COCH₃, COCF₃, and CF₃, the orbitals of the substituent and the upper orbitals of the ring do not interact.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 861–865, April, 1989.We thank A. A. Bliznyuk and A. A. Voityuk, for supplying the MNDO-86 program.     

Normal coordinate analysis of malononitriles: III. The valence force field of malononitrile and its deuterated derivatives

The procedure of Becher and Mattes [1] has been applied to the calculation of the valence force field for malononitrile H₂C(CN)₂ and its deuterated derivatives, HDC(CN)₂ and D₂C(CN)₂. The results have been localized in the space of the real solutions of the inverse vibrational eigenvalue problem. The convergence of the method has been demonstrated. The average deviation between observed and calculated frequencies on isotopic substitution is less than 1 %.     

The influence of charge localization on the isomerisation of organic ions

Collisional Activation Spectra demonstrate that gaseous n- and iso-pentyl ions isomerise completely to a common structure prior to decomposition while no or only partial isomerisation is found with the analogous heteroatom containing fragments, n- and iso-C₅H₁₁X⁺ (

), suggesting that the predominant localization of the charge at the heteroatom reduces the tendency for isomerisation.     

Control of cage opening reactions in the 1,3-bishomocubane and homocubane systems

The synthesis and base-induced cage opening of 5-fucctionalized homocubyl alcohols 22 (R is some protective group) is described. In a first approach, the synthesis of 22 has been attempted starting from tricyclic enol 14 and involving the Favorskii cage contraction of l,3-bishomocubanones 24. Unexpectedly, 4-methoxypentacyclo [5.3.0.0^2,5.0^3,9.0^4,8]decan-6-ones 24b and 29 undergo a facile add-catalyzed cage fragmentation to give tricyclo[5.3.0.0^2,5]decene diones 28a and b, respectively. The Favorskii cage contraction of 24 to homocubane carboxylic add 25c has been accomplished for the MEM-protected 24c, albeit in low yield. With silver cations under basic conditions, 24b and c undergo an unusual oxidative cage fission reaction leading to tetracyclo[4.3.0.0^2,4.0^3,8]nonan-5-one 7-carboxylic acids 40 and 41. An efficient route to 4-bromohomocubyl acetate 48 has finally been accomplished starting from 4,5-dibromo-l,3-bishomocubanone 43. Base-induced homoketonization of 48 is essentially directed by the 5-bromine atom and a regioapedfic cleavage of the central C₄–C₅ bond is observed, producing, in a stereospecific manner, 10-oxapeatacyclo [5.3.0.0^2,6.0^3,9.0^4,8]decane 51.     

The valence band of graphite monofluoride

Good agreement is shown to exist between the theoretically computed (modified extended Hückel) and the experimentally determined (X-ray photoelectron spectroscopy) density-of-states for graphite monofluoride.