Reaction of quinidine acetate, epiquinidine and its acetate in superacid : formation of gem-difluoro derivatives with or without rearrangement

Abstract In HF–SbF 5 , quinidine 1a or its dihydrochloride cyclises previously obtained with usual acids. A similar reaction is observed in the presence of CCl 4 . Under similar conditions quinidine acetate 1b and epiquinidine acetate 2b dihydrochlorides both yield 10,10-difluoro derivatives epimeric at C-3, 6 and 7 , and 9c and 10b , and a rearranged difluoro derivative 8b and 11b , respectively. Epiquinidine 2a leads to the expected analogues 10a and 11a and to a ketone 9a . Formation of gem -difluoro compounds implies chloro intermediates at C-10, precursors of α-chlorocarbenium ions, which are trapped by a fluoride ion and which lead by halogen exchange to the products.