A Novel Approach to 2,2‐Disubstituted 1,2‐Dihydro‐4‐phenylquinolines

The reaction of 2‐(1‐phenylvinyl)aniline and 4‐chloro‐2‐(1‐phenylvinyl)aniline with acetophenone derivatives, 1‐(naphthalen‐1‐yl)ethanone and 1‐(furan‐2‐yl)ethanone in toluene at 110–115° with toluene‐4‐sulfonic acid as a catalyst leads in good‐to‐excellent yields to the 2,2‐disubstituted 1,2‐dihydro‐4‐phenyl‐quinolines 1–18 ( Scheme 1, Table ). The structure of the new racemic 1,2‐dihydroquinolines 1–18 is determined by NMR spectroscopy. A reaction mechanism proceeding via a 6π‐electrocyclic rearrangement of 2‐(1‐phenylvinyl)anils 19 as the key step is proposed for the formation of these compounds ( Scheme 1 ). The scope and limitations of the novel methods are discussed ( Scheme 2 ).