Concise Enantioselective Total Synthesis of Cardiotonic Steroids 19-Hydroxysarmentogenin and Trewianin Aglycone.

The expedient and scalable approach to cardiotonic steroids carrying oxygenation at the C11- and C19-positions has been developed and applied to the total asymmetric synthesis of steroids 19-hydroxysarmentogenin and trewianin aglycone as well as to the assembly of the panogenin core. This new approach features enantioselective organocatalytic oxidation of an aldehyde, diastereoselective Cu(OTf)2-catalyzed Michael reaction/tandem aldol cyclizations, and one-pot reduction/transposition reactions allowing a rapid (7 linear steps) assembly of a functionalized cardenolide skeleton. The ability to quickly set this steroidal core with preinstalled functional handles and diversity elements eliminates the need for difficult downstream functionalizations and substantially improves the accessibility to the entire class of cardenolides and their derivatives for biological evaluation.