Carbenes Made Easy

Chemists have found a straightforward way to make rhodium azavinyl carbenes, a new family of reactive species for organic synthesis. To complement the existing tool kit of carbenes, which are high-energy intermediates capable of selective reactions, Valery V. Fokin and coworkers at Scripps Research Institute recently developed tunable azavinyl carbenes with unique synthetic capabilities (J. Am. Chem. Soc. 2009, 131, 18034). But making them involves sulfonyl azides and diazo compounds, which require very careful handling. Fokin, Neil Grimster, and Li Zhang have now devised a new route that gets around the hazardous compounds. From stable NH-triazoles, the one-pot procedure generates carbenes using triflic anhydride, a pyridine base, and a rhodium catalyst (J. Am. Chem. Soc., DOI: 10.1021/ja910187s). The rhodium azavinyl carbenes react with alkenes, yielding cyclopropanes or dihydropyrroles with good stereoselectivity. Avoiding potentially hazardous compounds “could greatly enhance the commercial and large-scale applications of rhodium carbenoid chemistry,” says Huw M. L. Davies, who studies carbenes at Emory University.