Tetranortriterpenoids. Part XVI. Partial syntheses of andirobin, methyl angolensate, mexicanolide, and 1-deoxymexicanolide

Abstract

Methyl angolensate (16; R = O) has been synthesised from 7-oxo-7-deacetoxykhivorin (2), thus confirming the proposed 1α-configuration of the ether oxygen atom. The diene lactone (11a) has also been prepared from the same starting material and it readily cyclises by Michael addition to give mexicanolide (18). 1-Deoxymexicanolide (25) has similarly been synthesised from 7-oxo-7-deacetoxygedunin (20). Partial syntheses of andirobin (17) and isoandirobin (19) are also reported.