The Reaction of Bicyclo [3.2.1] octenyl Halides with Metal Hydrides

Abstract

Abstract Reduction of 2‐phenyl‐ and 2‐methyl‐ exo ‐3,4‐dichlorobicyclo[3.2.1]oct‐2‐enes with lithium aluminium hydride (LAH) or tributyltin hydride (TBTH) gave endo ‐2‐phenyl‐3‐chlorobicyclo[3.2.1]oct‐3‐ene, 2‐phenyl‐3‐chlorobicyclo[3.2.1]oct‐2‐ene and their methyl analogues. The action of both reagents on 2‐phenyl‐ exo ‐3, 4‐dibromobicyclo[3.2.1]oct‐2‐ene similarly resulted in reductive monodebromination to give normal and allylically rearranged products. Additionally, further reduction occurred to give endo ‐2‐phenylbicyclo[3.2.1]oct‐3‐ene and 2‐phenylbicyclo[3.2.1]‐oct‐2‐ene. In all cases, LAH gave mainly the allylic rearrangement product whereas TBTH gave mostly unrearranged product. The reason for these differences could have been due either to the intervention of allylic radicals in the TBTH reduction or to differences in nucleophilicity. The results also show that LAH is equally efficaceous as TBTH in the reduction of these allylic halides and equally selective in the reduction of the vinyl bromides. The stereochemistry of the allylic rearrangement was shown to be synfacial in that hydride replaced halide on the same face of the molecule.