Convenient Synthesis of 2,2-Dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines

A convenient general synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines using the Wittig reaction is described. The o-nitrobenzaldehydes (1a–d) on reaction with phosphorane 2 provided ( E )-ethyl-α-(2,2-dimethylprop-2-ene)-2-nitrocinnamates (3a–d) in excellent yields, which on cyclization with polyphosphoric acid followed by reductive cyclization using Fe/HCl afforded dihydropyranoquinolines (5a–d). Alternatively, the pyranoquinolines 5a–d were also synthesised from esters 3a–d by employing domino reductive cyclization in a single step.