Formal Synthesis of (+)-Kopsihainanine A and Synthetic Study toward (+)-Limaspermidine.

The formal synthesis of (+)-kopsihainanine A has been achieved via stereoselective reduction of tetracyclic iminium ion intermediates (24). However, attempts to synthesize (+)-limaspermidine by reduction of the same tetracyclic iminium ion intermediates have failed. The synthesis features a Suzuki cross-coupling reaction, a cyclization reaction mediated by trifluoromethanesulfonic anhydride, and stereoselective reduction of an iminium ion.