New application of Pictet-Spengler reaction leading to the synthesis of an unusual seven-membered heterocyclic ring system

J Org Chem. 2005 Jun 10;70(12):4889-92. doi: 10.1021/jo050384h.

Abstract

A novel strategy for the Pictet-Spengler reaction is reported. Our strategy involves reaction of arylamines, linked to the N-1 of disubstituted imidazoles, with aldehydes in the presence of p-TsOH. The iminium ion generated in situ undergoes C-C bond formation with the C-5 of the imidazoles to furnish triazabenzoazulenes as a novel heterosystem. Our strategy differs from conventional Pictet-Spengler reaction since the latter utilizes only aliphatic amines in which the amine functionality is linked to a C instead of N of the activated aromatic moiety.