Synthesis of 2,3-Disubstituted Quinolines via Ketenimine or Carbodiimide Intermediates

Cyclopenta[b]quinolines and cyclohexa[b]quinolines were prepared via the reactions of alpha-diazo ketones with N-(2-cyclopropylidenemethylphenyl)phosphanimines and N-(2-cyclobutylidenemethylphenyl)phosphanimine, respectively. The reaction proceeds in a cascade involving ke-tenimine formation, 6 pi-electron ring closure, and 1,3-alkyl shift. A similar approach was developed for the synthesis of dihydropyrrolo-[2,3-b]quinolines from N-(2-cyclopropylidenemethylphenyl) phosphanimines and isocyanates.