S. Debarge, S. Thibaudeau, Bruno Violeau
Feb 21, 2005
Citations
0
Influential Citations
22
Citations
Journal
Tetrahedron
Abstract
Abstract In HF-SbF 5 , quinine 1a or its dihydrochloride rearranges into compound 3 (89%), the preferred conformation of the substrate favouring the observed cyclization. Under similar conditions epiquinine 2a dihydrochloride yields in equal amounts two 10,10-difluoro derivatives, epimeric at C-3. In this case, the more stable conformation of the substrate in which the benzylic hydroxyl group is ‘exo’ to the quinuclidyl moiety, prevents the cyclisation. Similarly acetates 1b and 2b give the corresponding 10,10-difluoro derivatives epimeric at C-3. Formation of gem -difluoro compounds implies the formation of chloro intermediates at C-10 followed by an hydride abstraction, yielding an α-chloronium ion. This one is trapped by a fluoride ion and leads to the product by halogen exchange.