Enantioselective Synthesis of Tropanes: Brønsted Acid Catalyzed Pseudotransannular Desymmetrization

Abstract

The enantioselective synthesis of tropanols has been accomplished through chiral phosphoric acid catalyzed pseudotransannular ring opening of 1-aminocyclohept-4-ene-derived epoxides. The reaction proceeds together with the desymmetrization of the starting material and leads to the direct formation of the 8-azabicyclo[3.2.1]octane scaffold with excellent stereoselectivity. The synthetic applicability of the reaction was demonstrated by the enantioselective synthesis of the two natural products (−)-α-tropanol and (+)-ferruginine.