An efficient intramolecular 1,3-dipolar cycloaddition involving 2-(1,2-dichlorovinyloxy)aryldiazomethanes: a one-pot synthesis of benzofuropyrazoles from salicylaldehydes.

A novel intramolecular 1,3-dipolar cycloaddition strategy for a rapid entry into benzofuropyrazoles is described. In a three-step sequence, (E)-2-(1,2-dichlorovinyloxy)aryldiazomethanes were generated in situ from the corresponding salicylaldehydes. Intramolecular cycloaddition followed by dehydrohalogenation garnered 3-chlorobenzofuropyrazoles in excellent yields. By careful choice of solvent, base, and reaction conditions, the entire sequence can be carried out in a one-pot procedure.