engleski

A cyclopropyl-homoallyl rearrangement accompanying the borane-mediated reduction of tosylhydrazones

The Wolff-Kishner reduction of strained cyclopropyl ketones 9-oxo-2, 8-didehydronoradamantane (1) and 5-oxo-2, 4-didehydrobrendane (5) proceeds without rearrangement, while the borane-mediated reduction of the corresponding tosylhydrazones la and 5a affords the rearranged products tricyclo[4.2.1.0(3, 8)]non-4-ene (3) and 4-brendene (7), respectively. Rearrangement also occurs during the reduction of the less-strained tosylhydrazones 8a and 10a derived from cyclopropyl methyl ketone (8) and bicyclo[4.1.0]heptan-2-one (10). The results obtained in experiments with deuterated reagents support a concerted mechanism of diazene decomposition/cyclopropyl-homoallyl rearrangement. This rearrangement offers a great possibility for the preparation of new polycyclic molecules and, moreover, is a convenient method for regiospecific isotopic labeling using deuterated reagents.

Small-ring systems; Hydrazones; Reduction; Rearrangements

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