Asymmetric total synthesis of (-)-lupinine and (+)-epilupinine via α-sulfinyl ketimine. Stereocontrolled reduction of β-sulfinyl enamines

Article abstract of DOI:10.1055/s-1991-26620

(-)-Lupinine and (+)-epilupinine [(1R,9aR)- and (1S,9aR)-octahydro-1-hydroxymethyl-2H-quinolizine] were synthesized from (+)-2,3,4,5-tetrahydro-6-[(R)-(4-methylphenyl)sulfinylmethyl]pyridine (4) in five steps. The intermediate, 3,4,6,7,8,9-hexahydro-1-[(R)-(4-methylphenyl)sulfinyl]-2H-quinolizine (7), was stereoselectively reduced with cerium(III) chloride heptahydrate and sodium borohydride to give predominantly C-9a-R isomers, (9aR)-octahydro-1-[(R)-(4-methylphenyl)sulfinyl]-2H-quinolizines.