Enantioselective Synthesis for the (−)-Antipode of the Pyrazinone Marine Alkaloid, Hamacanthin A

A short enantioselective total synthesis for the (-)-antipode of the antifungal marine alkaloid, hamacanthin A, (6R)-3,6-bis(6-bromoindol-3-yl)-5,6-dihydro-2(1H)-pyrazinone, is described. This synthesis proceeds through the coupling of 3-indolyl-alpha-oxoacetyl chloride and 3-indolyl azidoethylamine, followed by intramolecular aza-Wittig type cyclization. A concise and useful approach for the synthesis of (1R)-1-(indol-3-yl)-2-azidoethylamine using the Sharpless asymmetric dihydroxylation reaction followed by stereospecific azidation is also presented.