Development of highly stereoselective asymmetric 6π-azaelectrocyclization of conformationally flexible linear 1-azatrienes.: From determination of multifunctional chiral amines, 7-alkyl cis-1-amino-2-indanols, to application as a new synthetic strategy:: Formal synthesis of 20-epiuleine

The highly stereoselective asymmetric 6pi-azaelectrocyclization was achieved as a general synthetic method based on the reaction between the (E)-3-carbonyl-2,4,6-trienal compounds and the (-)-7-alkyl-cis-1-amino-2-indanol derivatives which are effective chiral amines. The 7-alkyl-substituted 2-indanol moiety of the cyclized products was efficiently removed by the novel manganese dioxide oxidation under remarkably mild conditions, and the method was successfully applied to the formal synthesis of optically active 20-epiuleine.