Abstract
Tandem Stille coupling and Diels−Alder reaction of steroidal iodoalkenyl substrates [17-iodoandrosta-16-ene (2), 17-iodo-3-keto-4-methyl-4-azaandrosta-16-ene (10), and 17-iodo-3-keto-4-azaandrosta-16-ene (11)] were examined in the presence of vinyltributyltin, a dienophile (diethyl maleate, methyl acrylate, dimethyl acetylenedicarboxylate, diethyl fumarate, (−)-di[(1R)-menthyl] fumarate, maleic anhydride), and a palladium catalyst. The yields of novel pentacyclic steroids and the stereochemical outcome of the cycloaddition reaction were investigated under different reaction conditions. In some cases mixtures of isomers were formed, but with dimethyl acetylenedicarboxylate, diethyl fumarate, (−)-di[(1R)-menthyl] fumarate, and maleic anhydride the products could be produced in good yields with high stereoselectivity. The unequivocal assignment of stereoisomers was carried out by various NMR techniques including 1H−1H COSY and NOE experiments.
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