Preparation of Nitro-Substituted 3-Benzylindoles via 3-Benzylideneindolines

Nitro-substituted 3-benzylindoles were obtained via piperidine-catalyzed Knoevenagel condensation of 4,6-dinitro-1-tosylindoline with aromatic/heteroaromatic aldehydes (yields 42-68 %) followed by a DBU-induced shift of the C=C bond thus formed into the 5-membered ring (yields 59-84 %). Nitro-substituted 3-benzylindoles were obtained via Knoevenagel condensation of 4,6-dinitro-1-tosylindoline with aromatic aldehydes with a subsequent isomerization resulting from a base-induced shift of the C=C bond into the 5-membered ring.image