Trifluoroacetic acid-mediated intramolecular formal N-H insertion reactions with amino-α-diazoketones: a facile and efficient synthesis of optically pure pyrrolidinones and piperidinones

Trifluoroacetic acid (TFA) was found to promote intramolecular formal N-H insertion reactions. Upon treatment with TFA, optically pure N-Boc-β'-amino-α-diazoketones (5a-c) and N-Boc-γ'-amino-α-diazoketones (10a-d) can be converted, with retention of chirality, into pyrrolidinones (11a-c) and piperidinones (12a-d), respectively, with concomitant removal of the Boc group, in good to excellent yields.