Selective Hydrogen Chloride Elimination from Primary Chlorides Induced by the Fluoride Anion. Anchimeric participation of the chloromethyl group in the heterolytic opening of an epoxide. Stereospecific syntheses of 5,6‐bis (methylidene)‐syn‐2‐norbornen‐7‐ol and 5,6‐bis (methylidene)‐endo‐3‐chloro‐exo‐2‐norbornanol

Abstract

SummarySyntheses of the alcohols 10 and 18, and the corresponding ketones 11 and 19 are presented. Endo-5, exo-6-bis (chloromethyl)-endo-3-chloro-exo-2-norbornanol (16) and endo-5-(bromomethyl)-exo-6-(chloromethyl)-endo-3-chloro-exo-2-norbornanol (17) were obtained by HC1-and, respectively, HBr-addition to endo-5, exo-6-bis (chloromethyl)-exo-2,3-epoxynorbornane (5). The Wagner-Meerwein rearrangement was precluded in these reactions probably because of the formation of a relatively stable chloronium ion 15 arising from the participation of the 1,Cchlorine atom of the endo-5-chloromethyl group in the heterolytic ring opening of the epoxide 5.The 'naked' fluoride anion (excess CsF in DMF or KF in DMF with 18-crown-6-ether) permitted the selective elimination of 2 equivalents of HC1 from 16 and yielded the chlorohydrin-diene 18.