Bispidine-derived N-acyliminium ions in synthesis: stereocontrolled construction of the BCD rings of sparteine

Reaction of Grignard reagents with bispidine-derived N-acyliminium ions (generated in situ from an α-methoxy bispidine amide) has been studied as a new route to sparteine analogues. The addition reactions proceed with complete diastereoselectivity to generate products with the same relative stereochemistry as in the BCD rings of sparteine. The first stereocontrolled synthesis of a tricyclic diamine structurally equivalent to the BCD rings of sparteine, is described.