μ-[3-4-η-(1-Alken-3-yne)hexacarbonyldicobalt complexes: Radical cyclocondensation mediated by manganese(III) acetate
摘要:
A regioselective pathway for the radical reaction of 1-alken-3-ynes with beta-dicarbonyl compounds, mediated by Mn(OAc)3, can be achieved by protection of the substrate triple bond with a hexacarbonyldicobalt moiety. Dihydrofuran and hexahydrobenzofuran derivatives are formed by intermolecular oxidative cyclization of intermediate cobalt-complexed propargyl radicals.
Cobalt cluster-directed, manganese(III)-mediated chemo- and stereoselective radical reactions of 1-alken-3-ynes
作者:Gagik G. Melikyan、Otto Vostrowsky、Walter Bauer、Hans Jurgen Bestmann、Masood Khan、Kenneth M. Nicholas
DOI:10.1021/jo00080a036
日期:1994.1
A new strategy has been developed to effect selective Mn(OAc)(3)-mediated oxidative cycloaddition reactions of 1-alken-3-ynes with beta-dicarbonyl compounds. The three-step sequence involves (1) protection of the triple bond of the substrate with the -Co-2(CO)(6) group, (2) Mn-promoted radical addition of the beta-dicarbonyl compounds with the complexed enyne, and (3) oxidative demetalation. Mono-, di-, and tricycles, containing 2,3-dihydrofuran and tetrahydrofuran rings, are produced by exclusive attack on the uncomplexed C=C in moderate overall yields; formation of bi- and tricyclic derivatives occurs with excellent cis-stereoselectivity. Molecular mechanics calculations indicate that the cis ring fusion in these systems is thermodynamically favored. Reactions of the Co-complexed substrates proceed with Mn(III) promotion alone, whereas the free enynes require combined Mn(III)/Cu(II) mediation to produce furan derivatives, apparently reflecting the relative ease of oxidation of the respective intermediate radicals to carbocations. For the complexed substrates direct experimental proof for the formation of free carbocations along the reaction coordinate has been obtained by methanol trapping.
MELIKYAN, G. G.;SARGSYAN, A. B.;BADANYAN, SH. O., ARM. XIM. ZH., 1986, 39, N 4, 228-233
作者:MELIKYAN, G. G.、SARGSYAN, A. B.、BADANYAN, SH. O.
DOI:——
日期:——
μ-[3-4-η-(1-Alken-3-yne)hexacarbonyldicobalt complexes: Radical cyclocondensation mediated by manganese(III) acetate
作者:Gagik G. Melikyan、Otto Vostrowsky、Walter Bauer、Hans Jürgen Bestmann
DOI:10.1016/0022-328x(92)83037-i
日期:1992.1
A regioselective pathway for the radical reaction of 1-alken-3-ynes with beta-dicarbonyl compounds, mediated by Mn(OAc)3, can be achieved by protection of the substrate triple bond with a hexacarbonyldicobalt moiety. Dihydrofuran and hexahydrobenzofuran derivatives are formed by intermolecular oxidative cyclization of intermediate cobalt-complexed propargyl radicals.