AN INTEGRATED APPROACH TO THE SYNTHESIS OF CONTIGUOUSLY SUBSTITUTED XANTHOPURPURINS, PACHYBASINS AND PURPURINS

Alkylation, hydroxyalkylation and acylation of 3-methyl-, 3-methoxy- and 3,4-dimethoxycrotonates can be induced to occur exclusively in the alpha-Position. Conversion of the products to dienes then provides, through cycloaddition, a wide variety of substitution patterns. This approach is illustrated by simplified syntheses of a number of naturally occurring quinones and confirms the structures proposed for vismiaquinone C, 7-geranylemodin, cinnalutein, 4,5-dihydroxydigitolutein, 2-hydroxyislandicin 1-methyl ether and calyculatone 1-methyl ether.