An Efficient Synthesis of 2,4-Disubstituted Quinolines by Electrophile-Mediated Cyclization Reactions of 2-Isocyanostyrene Derivatives

A novel quinoline synthesis starting with 2-isocyanostyrene derivatives is described. The treatment of 2-isocyanostyrene derivatives with aldehydes (or acetone) in the presence of a catalytic amount of diethyl ether–boron trifluoride afforded quinoline derivatives carrying a 1-hydroxyalkyl substituent at the 2-position. The use of acetaldehyde diethyl acetal or phenyloxirane as an electrophile under the same conditions gave the corresponding quinoline derivatives, carrying the 1-ethoxyethyl or 2-hydroxy-2-phenylethyl substituent at the 2-position, respectively. 2-Isocyanostyrene derivatives reacted with N,N-dimethyliminium salts without any catalyst to give 2-(1-dimethylaminoalkyl)quinolines.