Synthesis of 1,2-Dihydroquinolines via Hydrazine-Catalysed Ring-Closing Carbonyl-Olefin Metathesis

The synthesis of 1,2-dihydroquinolines by the hydrazine-catalysed ring-closing carbonyl-olefin metathesis (RCCOM) of N-prenylated 2-aminobenzaldehydes is reported. Substrates with a variety of substitution patterns are shown, and the compatibility of these conditions with a range of additives is demonstrated. With an acid-labile protecting group on the nitrogen atom, in situ deprotection and autoxidation furnishes quinolines. In comparison to related oxygen-containing substrates, the cycloaddition step of the catalytic cycle is shown to be slower, but the cycloreversion is found to be more facile.