Synthesis of novel tetracyclic pyrazolidinones from [3 + 2] cycloaddition of N-silyl enamines and azomethine imines

초록

Enamines are well-known as versatile structural motifs in organic synthesis which can be converted to various natural and pharmaceutical structures like amines, amidines and N-heterocycles. The recent research about hydrosilylation showed quinolines and isoquinolines were mildly reduced under boranecatalyzed hydrosilylation condition to accumulate endo N-silyl enamines as intermediates. In our previous research, we also utilized this intermediate to produce the corresponding cyclic amidines via a cycloaddition pathway. Herein, we continued this idea using N-silyl enamines from borane-catalyzed hydrosilylation as a precursor to develop the new synthetic strategies furnishing tetracyclic pyrazolidinones based on [3 + 2] cycloaddition with azomethine imines.