Competition between [1,7] hydrogen migration and electrocyclic ring closure in 6-methylhepta-1,3,5-triene

Abstract

(Z)-6-Methylhepta-1,3,5-triene and (Z,Z)-2-methylhepta-1,3,5-triene have previously been proposed as intermediates in the thermolysis of 5,5-dimethylcyclohexa-1,3-diene, the latter compound derived from the former by fast [1,7] antarafacial hydrogen migration in the gas phase. (Z)-6-Methylhepta-1,3,5-triene has now been synthesized and its thermal behaviour in the gas phase studied in the range 481–533 K. The thermal behaviour of both (Z)-6-methylhepta-1,3,5-triene and (Z)-2,7-dimethylocta-2,4,6-triene indicates that [1,7] hydrogen migration in acyclic trienes is not nearly as ready as has been previously postulated in the literature.