A concise and stereoselective synthesis of the BCDF tetracyclic ring system of C19-diterpenoid alkaloids.

Abstract

A new synthetic route for the BCDF tetracyclic ring system of C19-diterpenoid alkaloids (C19-DTAs) has been developed. The key step is a Pd-catalyzed transannular alkenylation that installs a functionalized bridged F ring. The overall strategy is concise and stereoselective, and it provides a valuable new tool for the synthesis of C19-DTAs. The synthesis begins with a bridged [3.2.1] ring system, which is converted to a key intermediate through a series of highly regio- and stereoselective processes. The introduction of an allylic side chain with high precision is accomplished, culminating in a Pd-catalyzed transannular alkenylation that installs a functionalized bridged F ring to yield the BCDF tetracyclic analog of C19-DTAs.