Synthesis Of 2,3-Disubstituted Quinolines Via Ketenimine Or Carbodiimide Intermediates

Ketenimines and carbodiimides are important intermediates in organic synthesis. There are mainly two reaction types through these intermediates. One is nucleophilic addition on the central carbon of ketenimine or carbodiimide through a step by step mechanism, and the other is the cycloaddition with an unsaturated component through a concerted mechanism. Based on the introduction of reported synthetic methods of ketenimines and their utilizations in building heterocyclic compounds, a new method was developed for the synthesis of 2,3-disubstituted quinolines via ketenimine or carbodiimide intermediates. The details are summarized as following:Cyclopenta[6]quinolines and cyclohexa[6]quinolines were prepared via the reactions of a-diazo ketones with N-(2-cyclopropylidenemethylphenyl) phosphanimines and N-(2-cyclobutylidenemethylphenyl) phosphanimine, respectively. The reaction proceeds in a cascade involving ketenimine formation,6π-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.