Carbene Chemistry. I. Stereochemical Integrity at C Alpha in Ketone Tosylhydrazones. II. Hydrogen Migration in 2-Carbena-6,6-Dimethylnorbornane

摘要

The tosylhydrazones of exo-3-deuteriocamphor and 2-deuterio-2,4-dimethyl-3-pentanone were treated with N-bromosuccinimide (NBS) and pyruvic acid to regenerate the parent ketones. The ketones from the pyruvic acid cleavage show a significant loss of deuterium. The ketones from the NBS cleavage show no loss of deuterium, indicating that stereochemical integrity at C sub alpha is maintained during the NBS cleavage. The tosylhydrazones and corresponding lithium salts of exo and endo-3-deuterio-6,6-dimethylnorbornan-2-one are found to maintain their stereochemical integrity at C sub alpha. Thermal and photolytic decomposition of the lithium salts reveals a 3,2 hydride migration preference of 19:1 in favor of the exo hydrogen. Torsional interactions in the hydride migration transition state of a classical singlet carbene are suggested as an explanation for the observed stereo-selectivity.