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

Ozonolyses of 1-alkyl-substituted 1-tert-butylethylenes and of highly methylated methylenecycloalkanes were conducted in the presence of trifluoroacetophenone () in ether. The ozonolysis of 2,2,6-trimethyl-1-methylenecyclohexane provided only the crossed-ozonide derived from capture of formaldehyde O-oxide with the ketone in 42% yield, while in the case of the relevant 2,2,5-trimethyl-1-methylenecyclopentane the alternative crossed-ozonide derived from cycloaddition of 2,2,5-trimethylcyclopentanone O-oxide with the ketone was the sole isolable product. The total energies of two possible cycloreversion processes for the primary ozonide and for , calculated at B3LYP/6-31G∗∗//B3LYP/3-21G∗ level of theory, seem to reproduce the observed difference in the regiochemistry of fragmentation between these two primary ozonides.