RING-D AROMATIC PHYTOSTEROIDS - A MODEL FOR BIOGENESIS BY WAY OF CARBON RADICAL REARRANGEMENT

A mechanism is postulated for the biogenesis of the unique ring-D arom atic phytosteroids from Nicandra physaloides, which involves rearrange ment, ring expansion, and aromatisation of a carbon radical generated by cytochrome P450 (Scheme 1). In support, model hydrindene acids 15b and 18b have been synthesized and subjected to homolytic decarboxylati on; the latter acid yielded 6-methyltetralin 24, in biomimetic fashion . The isomeric acid afforded not only 6-methyltetralin 24 but also 5-m ethyltetralin 26; mechanisms for this unusual rearrangement are discus sed.