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Paper | Special issue | Vol 84, No. 2, 2012, pp.893-911
Published online, 17th August, 2011
DOI: 10.3987/COM-11-S(P)70
Expedient Synthesis of 3,4-Dihydroquinazolines via Tandem Addition — Conjugate Addition Cyclization of Carbodiimides Bearing a Michael Acceptor

Takao Saito,* Hayato Nakano, Hidenori Terada, Noriki Kutsumura, and Takashi Otani

*Department of Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka 1-3, Shinjuku-ku, Tokyo 162-8601, Japan

Abstract

Michael acceptor-possessing N-phenylcarbodiimides, which were prepared by an aza-Wittig reaction of the corresponding functionalized iminophosphoranes with aromatic and aliphatic isocyanates, reacted with enolate carbon-nucleophiles of active methylene compounds via the tandem cumulene addition—hetero (NH) Michael addition cyclization, to provide 2,3,4-trisubstituted 3,4-dihydroquinazolines. It was also found that 2-aminoquinolines and 2-amino-3,4-dihydroquinolines were competitively formed in some cases. Based on these observations, possible mechanistic pathways leading to these heterocycles are proposed.