Step-Controlled Povarov-Type Reaction with 1,2-Dihydroquinolines as Precursors of Dienophiles: Direct Synthesis of Spirocyclic Bi-tetrahydroquinolines and Functionalized 1,2-Dihydroquinolines.

A novel Povarov-type reaction for straightforward synthesis of novel spiro bi-tetrahydroquinolines with readily available 1,2-DHQs (1,2-dihydroquinolines) and aromatic imines was developed. The reaction could be selectively stopped at the first stage under a Brønsted acid catalyst to afford the corresponding functionalized 1,2-DHQs conveniently.