Investigation of the Scope and Regiochemistry of Alkynylboronate Cycloadditions with Sydnones

The cycloaddition of alkynylboronates and sydnones provides a convenient and highly regioselective method for the synthesis of a broad range of di-, tri-, and tetrasubstituted pyrazole boronic esters. The origins of an observed regiochemical divergence in the reactions of terminal alkynylboronates with their more substituted analogues have been studied by DFT methods.