Efficient and Inexpensive Synthesis of 15 N-Labeled 2-Azido-1,3-dimethylimidazolinium Salts Using Na 15 NO 2 Instead of Na 15 NNN.

15 N-Labeled azides are important probes for infrared and magnetic resonance spectroscopy and imaging. They can be synthesized by reaction of primary amines with a 15 N-labeled diazo-transfer reagent. We present the synthesis of 15 N-labeled 2-azido-1,3-dimethylimidazolinium salts 1 as a 15 N-labeled diazo-transfer reagent. Nitrosation of 1,3-dimethylimidazolinium-2-yl hydrazine ( 2 ) with Na 15 NO 2 under acidic conditions gave 1 as a 1:1 mixture of α- and γ- 15 N-labeled azides, α- and γ- 1 , rather than γ- 1 alone. The isotopomeric mixture thus obtained was then subjected to the diazo-transfer reaction with primary amines 3 to afford azides 4 as a 1:1 mixture of β- 15 N-labeled azides β- 4 and unlabeled ones 4' . The efficient and inexpensive synthesis of 1 as a 1:1 mixture of α- and γ- 1 using Na 15 NO 2 instead of Na 15 NNN facilitates their wide use as a 15 N-labeled diazo-transfer reagent for preparing 15 N-labeled azides as molecular probes.