Limitations of the two-phase doebner-miller reaction for the synthesis of quinolines

The Doebner-Miller synthesis of quinolines under modified biphasic conditions was investigated. Crotonaldehyde, reacted readily with aniline to produce 2-methylquinoline. However, cinnamaldehyde and other γ-substituted α,β-unsaturated aldehydes yielded complex mixtures with substituted anilines to provide only trace quantities of quinolines. The Doebner-Miller reaction under these conditions is only suitable for sterically accessible α,β-unsaturated aldehydes.