An improved cobalt catalyst for homo Diels-Alder reactions of acyclic 1,3-dienes with alkynes

An efficient cobalt(I)-catalysed home Diels-Alder reaction of acyclic 1,3-d ienes and acetylene derivatives is described. The catalyst system consists of a mixture of a readily available CoBr2(dppe) complex, zinc iodide as a c ocatalyst, and tetrabutylammonium borohydride as reducing agent. This syste m increases the reactivity of the cobalt(I) catalyst, so that acyclic diene s and acetylenes can be transformed to the 1,4-dihydroaromatic products in good yield and excellent purity. The regioselectivity of the home Diels-Ald er reaction greatly favours the 1,4-substitution pattern of the formed prod uct. (C) 2000 Elsevier Science Ltd. All rights reserved.