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.
2010
Abstract 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-1-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 regiochemistry of fragmentation between these two primary ozonides.
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