The intermolecular cyclotrimerisation of terminal and internal alkynes can be catalysed by simple cobalt complexes such as a CoBr2(diimine) under mild reaction conditions when treated with zinc and zinc iodide with high regioselectivity in excellent yields.
An efficient cyclo-codimerization between 1,3-diene and non-activatedterminal acetylene has been attained by the catalysis of [Rh(COD)(DPPB)]PF6 to give 1,4-disubstituted cyclohexa-1,3-dienes under mild conditions.
An improved cobalt catalyst for homo Diels–Alder reactions of acyclic 1,3-dienes with alkynes
作者:Gerhard Hilt、François-Xavier du Mesnil
DOI:10.1016/s0040-4039(00)01163-1
日期:2000.8
cobalt(I)-catalysed homo Diels–Alder reaction of acyclic1,3-dienes and acetylene derivatives is described. The catalyst system consists of a mixture of a readily available CoBr2(dppe) complex, zinc iodide as a cocatalyst, and tetrabutylammonium borohydride as reducing agent. This system increases the reactivity of the cobalt(I) catalyst, so that acyclic dienes and acetylenes can be transformed to the
Reactions of Alkynyldihaloboranes with 1,3-Dienes. 1,4-Alkynylborations and Stepwise Diels−Alder Reactions
作者:Shun-Wang Leung、Daniel A. Singleton
DOI:10.1021/jo961892h
日期:1997.4.1
alkynylstannanes. The Diels-Alder reactions of 1-4 with isoprene in hexanes proceed rapidly at 25 degrees C, affording 1,4-cyclohexadiene products in high yield with high regioselectivity. Reactions carried out in CH(2)Cl(2) exhibited an alternative product that results from the formal 1,4-alkynylboration of the diene. The alkynylboration intermediates can undergo further conversion to the Diels-Alder adducts under
Ligand and solvent effects on cobalt(I)-catalysed reactions: Alkyne dimerisation versus [2+2+2]-cyclotrimerisation versus Diels–Alder reaction versus [4+2+2]-cycloaddition
bromide complex, zinc and zinc iodide in acetonitrile. With 2–5 mol% of the cobalt catalyst at ambient temperatures 1,2,4-triphenylbenzene could be obtained in 99% yield and in excellent regioselectivity (95:5) in 10 min reaction time. Competition experiments of phenylacetylene and isoprene were performed. A preference for the cyclotrimerisation reaction was found for the diimine cobaltcomplex in acetonitrile