Ozonolyses of 1-alkyl-substituted 1-tert-butylethylenes and highly methylated methylenecycloalkanes. The influence of the substituent steric bulk on the direction of cleavage of the primary ozonides

摘要

Ozonolyses of 1-alkyl-substituted 1-tert-butylethylenes and of highly methylated methylenecycloalkanes were conducted in the presence of trifluoroacetophenone (7) in ether. The ozonolysis of 2,2,6-trimethyl-1-methylenecyclohexane provided only the crossed-ozonide 10 derived from capture of formaldehyde O-oxide with the ketone 7 in 42% yield, while in the case of the relevant 2,2,5-trimethyl-l-methylenecyclopentane the alternative crossed-ozonide 15e derived from cycloaddition of 2,2,5-trimethylcyclopentanone O-oxide with the ketone 7 was the sole isolable product. The total energies of two possible cycloreversion processes for the primary ozonide 12c and for 12e, calculated at B3LYP/6-31G**//B3LYP/3-21G* level of theory, seem to reproduce the observed difference in the regio-chemistry of fragmentation between these two primary ozonides. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 29]