Enantioselective total synthesis of phomallenic acid C.

The newly isolated bacterial FAS II inhibitor phomallenic acid C (3) was synthesized for the first time as a 16:1 mixture of the (R)- and (S)-isomer with the diyne-allene motif constructed using a coupling under Negishi conditions. By comparison with the synthetic sample, the natural phomallenic acid C was estimated to be a 3.8:1 mixture of (R)-/(S)-isomers. This synthesis describes a new synthetic entry to optically active allene diynes.