Regioselective Carbon–Carbon Bond Formation in the Effector Domain of Ascomycin

Starting from 33-O-silyl-protected ascomycin or its 23,24-dehydration product, regio- and stereo-selective formal aldol reactions under carbon–carbon bond formation at C-22, C-23, or C-24 are demonstrated. Additionally, with the 22-silyl enol ether ascomycin derivative a rhodium(I)-catalysed shift of the 19,20 double bond into the 19,38 exocyclic position is observed at elevated temperature.