Regioselective cycloaddition of trifluorodiazoethane with electron-deficient allenic esters and ketones: Access to CF3- substituted pyrazolines and pyrazoles
A highly regioselective cycloaddition procedure of electron-deficient allenes with trifluorodiazoethane (CF3CHN2) is described. In absence of bases, the reaction proceeded smoothly to give 5-(trifluoromethyl)pyrazolines, whereas the utility of Et3N led to the formation of 3-(trifluoromethyl)pyrazoles.