A Biomimetic Approach to the Discorhabdin Alkaloids: Total Syntheses of Discorhabdins C and E and Dethiadiscorhabdin D.

The characteristic spirodienone structure of the discorhabdin alkaloids is readily formed by reaction of the tyramine-substituted indoloquinonimines 26, 35, and 36 with cupric chloride, triethylamine, and oxygen. This cyclization provides a possibly biomimetic route to discorhabdins C and E (41 and 42). The unbrominated spirodienone 40 reacts with hydrogen over Pd/C to give enone 46. Bromination at the alpha position gives a mixture of bromoenones that undergo smooth conversion to dethiadiscorhabdin D (4) upon treatment with basic alumina.