No abstract

Standard enthalpies Δf H 298, entropies S 298, and Gibbs functions of formation Δf G 298 for a large number of silicon hydrides containing one to five Si atoms have been calculated. The choice of compounds includes cyclic and acyclic silanes, silyl radicals, silylenes, disilenes, and cyclic diradicals. The thermodynamic functions were calculated using an empirically corrected ab initio scheme. The electronic energies were obtained with multiconfiguration reference averaged coupled-pair functional (ACPF) wave functions. Two different basis sets were employed to demonstrate the validity of the correction scheme. The computed data are compared with experimental and theoretical data from other laboratories. Increment rules and substituent effects are presented and various reaction enthalpies are tabulated and discussed. The performance of the correction scheme and potential pitfalls in its general applicability are discussed.

group in 14c has been introduced for two reasons: firstly, for the later conversion of the photolactones 4 and 6 into the stereoisomeric dienone lactones and, secondly, to achieve regioselective Wessely acetoxylation. The oxidation of 14c with Pb(OAc),, however, must then be catalyzed by Lewis acid: with BF3.ether in a mixture of methanol and ethyl acetate["I the o-quinol acetates 1 and 3 are isolated in 85% yield.To sum up: the synthesis of 8 shows, for the first time, how useful photolactonization for the synthesis of macrolides really is and, once again, that in a cyclic system the information of a remote center of chirality can be transmitted to a high degree to a newly developing stereogenic center.

No abstract

No abstract