A new synthetic method for the framework of aspidosperma alkaloids using singlet oxygen chemistry

Abstract1-A singlet oxygen adduct of l-benzyloxycarbonyl-l, 2-dihydro-5-(2-methyl-l,3-dioxolan-2-yl)pyridine 21 was treated with indole in the presence of stannous chloride to yield directly the complex compound 22, which will act as a suitable starting material for the synthesis of various kinds of indole alkaloids. Further transformation from 22, including a new device for construction of the aspidosperma framework, was investigated and pentacyclic compounds 25 (Y = H and OH) were synthesized in moderate yields. The structure of 25 (Y = H) = 38 was confirmed by correlation with l-acetyl-20-deethylaspidospennidine 44. Determination of the structure of a by-product 39 was carried out by single crystal X-ray analysis.