A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (-)-cephalimysin A.

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(-)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A.