Povarov reaction

In step one aniline and benzaldehyde react to the Schiff base in a condensation reaction.

Two additional elimination reactions create the quinoline ring structure.

This is in contrast to traditional Diels–Alder reactions, which are stereospecific based on the alkene geometry.

In 2013, Doyle and coworkers reported a Povarov-type, formal [4+2]-cycloaddition reaction between donor-acceptor cyclopropenes and imines (Scheme 3).

Scheme 4 depicts this 4 component reaction with the ethyl ester of glyoxylic acid, 3,4-dihydro-2H-pyran, aniline and ethanol with lewis acid scandium(III) triflate and molecular sieves.

Scheme 1. The Povarov reaction
Scheme 2. regio- and diastereoselective Povarov reaction
Donor-acceptor cyclopropene formation and subsequent [4+2] cycloaddition to yield cyclopropane-fused tetrahydroquinolines. Subsequent treatment with TBAF opens the cyclopropane ring to give benzazepines.
Scheme 4 Four component Povarov reaction. In order to clarify the role of the lewis acid, a solid scandium nitrogen bond is drawn. Reaction conditions 2 days in acetonitrile at room temperature