Novel ring transformation of quinolines to indole derivatives in two steps via 1,4-dihydroquinoline derivatives

Diphenyl 1-phenoxycarbonyl-1,4-dihydroquinoline-4-phosphonates 5c-g, obtained from the reaction of corresponding quinoline derivatives 1 with phenyl chloroformate and triphenyl phosphite in one step, were ozonized in CHCl₃ and CH₃COOH. Treatment of the resulting mixture with NaHCO₃ produced the 3-formyl-1-phenoxycarbonylindole derivatives 8a-e in high yields. The ring transformation of quinolines 1 to indoles 8 proceeds under mild conditions.