Total Synthesis of (−)-Solanapyrone A via Enzymatic Diels−Alder Reaction of Prosolanapyrone

The syntheses of prosolanapyrones I ( 6 ) and II ( 7 ) via the aldol reactions of pyrone and dienal segments have been achieved in five steps in 31% overall yield for 6 and seven steps in 5% overall yield for 7 . An improved synthetic route starting from vinylpyrone 27 provided 7 in 11 steps in 12% overall yield. The enzymatic Diels−Alder reaction of 7 affords (−)-solanapyrone A ( 1 ) with high enantioselectivity and with good exo-selectivity, which is difficult to attain by chemical methods. In addition, a crude enzyme preparation from Alternaria solani has been used to perform a kinetic resolution of (±)- 3 .