Syntheses of batzelline A, batzeline B, isobatzelline A, and isobatzellineB

Batzellines A and B (la, b) and isobatzellines A and B (2a, b) are 1,3,4,5- tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characteri zed by the presence of a methylthio substituent at C-2 of the tricyclic sys tem. We describe here the total synthesis of these natural compounds follow ing the synthetic strategy that we have used previously for the synthesis o f damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and mak aluvamines A, B, C, and D. The introduction of the methylthio group by elec trophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately subst ituted and in a suitable oxidation state, is the key step in the success of these syntheses.