Journal of the American Chemical Society p. 3659 - 3671 (1989)
Update date:2022-08-11
Topics:
Stone, Keith J.
Greenberg, Marc M.
Blackstock, Silas C.
Berson, Jerome A.
The title biradicals 1 and 2 are generated in solution by thermal or photochemical decomposition of the corresponding diazenes, 1,4-dihydrofurano<3,4-d>pyridazine (15) and 1,4-dihydrothieno<3,4-d>pyridazine (16), whose syntheses are described.The biradicals both dimerize, but in the presence of trapping agents, both react with electron-deficient alkenes to form furano(thieno)<3,4-d>cyclohexanes (fused adducts).The furan biradical 1, however, gives predominantly a bridged adduct.The cycloadditions are strictly stereospecific and seem to occur by concerted four-centertransition states.Competition studies show that the relative reactivities of alkenes toward the thiophene biradical 2 are quantitatively the same whether the biradical is generated from the diazene precursor 16 or from diallenyl sulfide 6.The latter observation confirms earlier proposals in the literature that biradical 2 could be involved in the chemistry of 6.The reactivity order of the biradicals parallels that of cyclopentadiene toward the test series of alkenes, the selectivities in both series showing a near-unit slope in a bilogarithmic plot, despite the factor of 1E10 by which the biradical absolute rates exceed those of the diene.
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