INAPPLICABILITY OF THE ANTIPERIPLANAR LONE PAIR HYPOTHESIS TO C-P BOND BREAKING AND FORMATION IN SOME S-C-P+ SYSTEMS

摘要

Both C(2)-P bond breaking and formation in the S-C-P+ system do not occur according to the antiperiplanar lone pair hypothesis. Experiments using 2-phosphonio derivatives of 5-tert-butyl-1,3-dithiane and cis-4,6-dimethyl-1,3-dithiane are against the participation of higher-energy boat conformers as reactive intermediates. The results obtained support a possibility of conformational adjustment in the course of the reaction. Stereoelectronic control of the C(2)-P bond breaking and formation results from interplay of several factors. The role of the n(S)-sigma*(C(2)-P) and sigma(C(4,6)-S-) sigma*(C(2)-P) hyperconjugation, as well as of the repulsive interactions between lone electron pairs pi(S) of endocyclic sulfur atoms and pi-electrons of the phenyl ring(s) connected with phosphorus, is discussed. [References: 60]