Hydrogen Migrations in a Constrained Cyclohexylidene. Hax/Heq Shift Ratios in Thermal and Photic Bamford-Stevens Reactions

Article abstract of DOI:10.1016/S0040-4020(01)88030-3

Homobrexan-2-one was synthesized labeled in the α-position with 13C and also with an axial or equatorial D.Their p-tosylhydrazone Li salts were thermolyzed and photolyzed (Bamford-Stevens reaction) to generate putative singlet carbenes, which undergo competitive 1,3-insertion to a tetracycle and 1,2-H (or D) shift to an alkene.After correction for isotope effects, the H_ax/H_eq shift ratios were ca. 1.7 and ca. 1.2 for the thermal and photic processes, respectively.These ratios are free of chair-boat and epimerization ambiguities.