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In alkene-directed, nickel-catalyzed coupling reactions of 1,3-enynes with aldehydes and epoxides, the conjugated alkene dramatically enhances reactivity and uniformly directs regioselectivity, independent of the nature of the other alkyne substituent (aryl, alkyl (1 degrees , 2 degrees , 3 degrees )) or the degree of alkene substitution (mono-, di-, tri-, and tetrasubstituted). These observations are best explained by a temporary interaction between the alkene and the transition metal center during the regioselectivity-determining step. The highly substituted 1,3-diene products are useful in organic synthesis and, in conjunction with a Rh-catalyzed, site-selective hydrogenation, afford allylic and homoallylic alcohols that previously could not be prepared in high regioselectivity (or at all) with related Ni-catalyzed alkyne coupling reactions.
Miller et al. (Tue,) studied this question.