Unexpected formation and crystal structure of a spiro[indene-1,7′(6′H)pyrrolo[3,4-b]pyridin]-5′-one

Abstract

Dehydration of 6,7-dihydro-7-hydroxy-6-(α-methylbenzyl)-7-phenylpyrrolo[3,4-b]pyridin-5-one 4b on treatment with acid is accompanied by rearrangement, first to 6,7-dihydro-7-phenyl-7-[(E)-2-phenylethenyl]pyrrolo[3,4-b]pyridin-5-one 10 and then to 2,3-dihydro-3-phenylspiro[indene-1,7′(6′H)-pyrrolo[3,4-b]pyridin]-5′-ones 9a, b. Crystal structures of two rearranged products 9a and 10 are reported.