Sydnone-Based Approach To Heterohelicenes Through 1,3-Dipolar-Cycloadditions

The first approach to pyrazole-containing helicenes via sydnone-aryne [3 + 2]-cycloaddition is described. An unprecedented regioselectivity in the cycloaddition step toward the more sterically constrained product was observed in the presence of extended aromatic scaffolds. DFT calculations enabled under-standing the origin of this unexpected selectivity.