Annulations of Podocarpic Acid Derivatives via an Aryne Intermediate

Abstract

The cycloaddition of substituted furans to the diterpenoid aryne (39), generated by in situ diazotization of the anthranilic acid (1) followed by cleavage of the annulated 1,4- epoxydecahydrochrysenes, provides a convenient method for the preparation in high yield of the previously unknown 1-substituted octahydrochrysen-4-ols. Use of 1,3-dipoles under the same procedure, or under a modified procedure involving pre-isolation of the diazonium tetrafluoroborate salt (9), gave novel annulated heterocyclic products directly. Attempted [2+2] cycloadditions of electron-rich alkenes to the diterpenoid aryne (39) were largely unsuccessful but reaction with 1,1-dimethoxyethene by using in situ diazotization gave a product derived from an initial [2+2] cycloaddition.