Studies on the synthesis of Aspidosperma and related alkaloids. Part II. A synthetic approach to the C-21 oxygenated Aspidosperma alkaloids
Abstract
An attempt was made to extend the total synthesis of (±)-aspidospermine (I) to the synthesis of (±)-limaspermine (IV). An eleven-step scheme starting from 5-phenoxypentan-2-one (XIV) gave (±)-21-phenoxyisopalosine (XXXIX), which was treated with hydrobromic acid to furnish the quaternary salt (XLII). The formation of this salt suggests that the stereochemistry of our products is not identical with that of the natural alkaloid.