On Pd-catalyzed cycloisomerization versus cycloreduction. A general strategy for drimane synthesis and a short total synthesis of siccanin

The Pd-catalyzed reductive cyclization of diynes represents an attractive alternative to the Pd-catalyzed cycloisomerization to 1,3-dienes. By minimization of steric constraints, cyclizations that fail in the latter case may now succeed. For the cycloreduction, a more general protocol in which formic acid is the key has now emerged. In the first test of this reductive cyclization to solve a problem of complex synthesis, the reaction performed exceptionally well. The dialkylidenecycloalkanes that result have great versatility, especially with respect to the type of functionality commonly found in the drimanes. Both the cis and trans ring fused drimanes might be available.