α-(N-Alkyl-N-heteroarenium)-α-diazoacetates: synthesis and reactivity of a novel class of ‘onium’ diazo compounds†

Treatment of alkyl α-(N-heteroaryl)-α-diazoacetates with alkylating reagents affords diazoacetate N-heteroarenium salts. These novel ‘onium’ diazo compounds are mostly yellow solids, displaying increased thermal and acid stability. Their tetrafluoroborates undergo rhodium catalyzed [2 + 1] and Doyle–Kirmse reactions under mild conditions, suggesting the N-quaternization an effective means of elimination of N-coordination caused catalyst toxicity.