Asymmetric Total Synthesis of ent-Pyripyropene†A.

An asymmetric total synthesis of ent-pyripyropene A was achieved by a convergent synthetic route. We used our originally developed Ti(III) -catalyzed radical cyclization to construct an AB-ring portion that consisted of a trans-decalin skeleton with five contiguous stereogenic centers. The coupling between the AB-ring and the DE-ring portions, and a subsequent C-ring cyclization, led to the total synthesis of ent-pyripyropene A. An evaluation of the insecticidal activity of ent-pyripyropene A against two aphid species revealed that ent-pyripyropene A was 35-175 times less active than naturally occurring pyripyropene A. This result indicated that the biological target of pyripyropene A recognizes the absolute configuration of pyripyropene A.