TFA-induced dimerization of indole-3-acetic acid (IAA) gave 5a. The co
rresponding methyl ester gave the diester 5b or the lactam 6. Similar
treatment of the 2,3-bis(3-indolyl)-succinic ester 4b gave the tetrahy
droindolo [2,3-a]carbazole derivative 10. The relation of these compou
nds to indolocarbazole alkaloids is discussed.