On the Problem of Regioselectivity in the 1,3-Dipolar Cycloaddition Reaction of Munchnones and Sydnones with Acetylenic Dipolarophiles

Article abstract of DOI:10.1021/jo00344a008

The 1,3-dipolar cycloaddition reaction of several unsymmetrically substituted munchnones and sydnones with methyl propiolate has been examined.The initially formed cycloadducts readily extrude carbon dioxide to produce five-membered heteroaromatic ring compounds.The reaction of sydnones with methyl propiolate produced a mixture of regioisomeric pyrazoles.The analogous <3 + 2> cycloaddition reaction of munchnones with methyl propiolate proceeds with formation of mixtures of both possible regioisomeric pyrroles.The structural assignment of the isolated adducts is based on spectroscopic data.The distribution of products depends on the nature and location of the substituent groups present on the heterocyclic ring.The observed regioselectivity is discussed on the basis of MO-perturbation theory.