Alkenylzinc organometallics

The addition of organometallics to internal alkynes is rare [75-77] and proceeds with moderate stereoselectivity [76]. In the presence of a nickel catalyst such as Ni(acac)2, it is possible to add diorganozincs to substituted phenylacetylenes. This recently reported reaction proceeds with high stereoselectivity (>99% s yn-addition) and is often highly regioselective. The resulting alkenylzinc organometallics can be quenched with several types of electrophiles (Scheme 9-39) [78],... 

The use of alkenylzincs as excellent organometallic partners in Pd-catalyzed alkmyl-alkenyl coupling has amply been demonstrated. In most cases, reactions proceed smoothly to produce the desired products in excellent yields and high stereoselectivities, as exemplified by the synthesis of methyl dimorphecolates shown in Scheme... 

The other organometallic compounds, such as alkynylcoppers, alkenylzincs, and alkenylzirconocenes, have also been utilized for the tran -selective couphng reaction of 1,1-dihaloalkenes (Scheme 4). The monoalkynylation of 1,1-dichloroethylene in the presence of palladium and copper catalysts is troublesome. Since dialkynylation is not easily suppressed, an excess amount of the substrate, 1,1-dichloroethylene, is required to produce the desired product. 

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