Reciprocal Tests of Steric Opposition to Down-Disrotatory Thermal Decyclization of Propellanes. The Cycloreversion Stereochemistry of the 6,7,8-Trimethyltricyclo1,5>octanes

Article abstract of DOI:10.1016/S0040-4039(00)80621-8

The syntheses and thermal decompositions of the isomeric title compounds are described.The cis, endo isomers undergo down-disrotatory cycloreversion to E,E-2-methyl-1,3-bis-(ethylidene)-cyclohexane with high stereospecificity, regardless of the stereochemistry of the C₈-methyl group.Both 8-syn- and 8-anti-6,7-trans-trimethyl isomers decyclize with low stereochemical preference, suggesting that the orbital overlap factors favoring the down-disrotatory path in the cis cases may be overcome easily by steric effects.