A unified asymmetric approach to substituted hexahydroazepine and 7-azabicyclo[2.2.1]heptane ring systems from D(−)-quinic acid: Application to the formal synthesis of (−)-balanol and (−)-epibatidine

Abstract

3,4- O-Isopropylidene-3( R),4( S)-dihydroxycyclohexanone 7, a chiron easily prepared through a five step sequence from D(-)-quinic acid 1, has been efficiently utilized as the starting building block for the enantioselective syntheses of (3 R,4 S)- N- p-toluenesulfonyl-3,4-epoxy-hexahydroazepine 17 and (1 R,4 S)- N- tert-butoxycarbonyl-7-azabicyclo[2.2.1]heptan-2-one 43, advanced intermediates already taken to (-)-balanol and (-)-epibatidine respectively. While the nitrogen atom ring-insertion via Beckmann rearrangement was the key step for the construction of the hexahydroazepine ring of 17, a regio- and stereospecific intramolecular nucleophilic ring opening of an intermediate cyclic sulfate featured the approach to the substituted 7-azabicyclo[2.2.1]heptane nucleus of 43.