BIS(INDOLE) ALKALOIDS - A NONBIOMIMETIC APPROACH TO THE BLUE PIGMENT TRICHOTOMINE DIMETHYL ESTER

Two alternative routes have been developed for the synthesis of trichotomine dimethyl ester 2. Both routes involve the synthesis of keto lactam 3 by reaction of the chiral imine 4 [obtained starting from (S)-(-)-tryptophan] with oxalyl chloride. The elaboration of 3 into 2 is achieved through the intermediacy of diazo lactam 5 and subsequent copper-assisted thermolysis furnishes 2. A more efficient route involves a carbene-mediated olefination of keto lactam 3 to give trichotomine dimethyl ester 2 in good yield. The preparation of decarboxytrichotomine 6 is also described.