Stereochemistry of Additions of m-Quinomethane to Olefins and Acyclic Dienes

Article abstract of DOI:10.1021/ja00272a039

The m-quinomethane biradical has a triplet ground state, as judged by the temperature dependence of the intensity of its EPR signal.When generated by pyrolysis or photolysis of 6-methylenebicyclo<3.1.0>hex-3-en-2-one, it adds to olefinic trapping agents to give phenolic indans.Retention of configuration dominates by a factor of 13-17 with cis-1,2-dimethoxyethene and by a factor of >100 with trans-1,2-dimethoxyethene.With the 2,4-hexadienes, which undergo addition to give phenolic 1-propenylindans, retention again is the favored pathway, but the preference is lower (up to 6-fold).The propenyl stereochemistry in the product is completely retained.A comparison with known results of cycloadditions of trimethylenemethane (singlet) biradical and of m-quinodimethane shows that m-quinomethane additions are intermediate between the other two in cis stereospecifity.A mechanistic rationale for this ordering is discussed.