One-pot, two-step conversion of alkynes to alpha-amino (alpha,alpha-diamino) ketones with a DMF-activated N-bromoimide strategy

A simple, one-pot, two-step cascade reaction for the synthesis of alpha-amino ketones has been developed. Both terminal and internal alkynes react with DMF-activated N-bromosuccinimide (phthalimide) and water (as external O-nucleophile), followed by the introduction of DBU, giving imidated ketones efficiently (the N-sources arise from inherent N-haloimides). Monoamino ketones were the main products with NBS. Mono and/ or diamino ketones are produced when NBP is utilized. A mechanism of sequential oxy-1,1-dibromogenation of alkynes, nucleophilic substitution and reductive debromination (or second nucleophilic substitution) is proposed.