An efficient, facile, and general synthesis of 1H-indazoles by 1,3-dipolar cycloaddition of arynes with diazomethane derivatives

(Chemical Equation Presented) Take your pick: Both N-unsubstituted and 1-aryl 1H-indazoles are available in good to high yields through the [3+2] cycloaddition of benzynes derived from o-silylaryl triflates with diazomethane derivatives (see scheme). In the presence of KF/[18]crown-6, the N-unsubstituted 1H-indazole is formed, whereas the 1-arylated product is obtained regioselectively with CsF and an excess of the triflate.