Reduction of 7-Methyl- and 7-Phenyl-7-halobicyclo- [4.1.0] heptanes with Tributyltin Hydride

Abstract

Each of the two geometrical isomers (1a and 1b) of 7-chloro-7-methylbicyclo-[4. 1. 0] heptane and the endo-methyl isomer (2a) of 7-bromo-7-methylbicyclo [4. 1. 0]-heptane were separately reduced with tributyltin hydride in a temperature range of 0 to 140°C, to give an isomeric mixture of 7-methylbicyclo[4. 1. 0]heptane (5). The endo : exo ratio in the product was 72±2 : 28±2, irrespective of the geometry of the starting halide. The reduction of 7-chloro-7-phenyIbicyclo [4. 1. 0] heptane (3) under similar conditions also proceeded nonstereospecifically to afford an isomeric mixture of 7-phenylbicyclo[4. 1. 0]heptane (6) with the endo : exo ratio of 90±2 : 10±2. The complete loss of stereospecificity in these reductions suggests that the intermediarily formed 7-methyl- and the 7-phenylbicyclo [4. 1. 0] hept-7-yl radicals are configurationally unstable and behave like a planar radical.