Development of Highly Stereoselective Asymmetric 6π-Azaelectrocyclization of Conformationally Flexible Linear 1-Azatrienes. From Determination of Multifunctional Chiral Amines, 7-Alkyl <i>cis</i>-1-Amino-2-indanols, to Application as a New Synthetic Strategy: Formal Synthesis of 20-Epiuleine
The highlystereoselective asymmetric 6π-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