STEREOCHEMISTRY OF DIMERIZATION OF INDOLE-3-ACETIC-ACID AND ITS PROPYL ESTER

The mechanism, stereochemistry and products of the dimerisation of ind ole-3-acetic acid 1a and its propyl ester 1b in TFA and H3PO4 have bee n investigated. The major products in both acids were 2-(indolin-2-yl) indole dimers, 3a/b, which were readily converted into the correspondi ng pentacyclic lactams 5a/b with the pyrido[1,2-a:3,4-b']biindole skel eton. Ccompound 5a was studied by X-ray crystallography and shown to b e the 2,3-trans-isomer. The reaction proceeds via electrophilic attack of the protonated species 2 on free 1 with steric approach central to form the trans-stereoisomeric 3 and/or 5.