[2,3] Fused indoles. Part 2. Synthesis of 1,8-dihydropyrrolo[2,3-b]indoles, and photochemical rearrangement of their 1-allyl derivatives

Abstract

1,8-Dihydropyrrolo[2,3-b]indoles (6) are prepared in three steps from indole-3-carbaldehyde via the azidoacrylates (2). The 2-ester substituent is readily hydrolysed and decarboxylated, whereas attempted reduction leads to bis(pyrroloindolyl)methanes (16). The 1-allyl (21), methylallyl and prenyl derivatives (24a) and (24b) undergo photochemical rearrangement to the 2H-isomers (23), (25a), and (25b) respectively in a reaction typical of pyrroles.