Cardenolide Knoevenagel reaction

Steroidal ketones have been used extensively in the Knoevenagel reaction. Thus, die transformation of 17-oxoandrostane derivatives (309), which are readily available by microbiological degradation of sitosterin, are employed for the synthesis of enantiomerically pure cardiotonic steroids such as bufa-dienolide and cardenolide (311). In toth syntheses the substitutent at C-17 is introduced by a Knoevenagel reaction of the 17-oxoandrostane derivative (309) with ethyl cyanoacetate in the presence of ammonium acetate to give the cyano ester (310), presumably as a mixture of the ( )- and (Z)-isomers, in 89% yield.5 5... 

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