Reactions of Enones with Alkynes

Nickel catalyst has been shown to be effective for the three-component couplings of alkynyltins with enones and alkynes leading to stereodefmed conjugated enynes in good yields [156-158]. DIBALH is used to generated active nickel catalyst for this transformation. It is noteworthy that enones can be either cyclic or acyclic. 

In this reaction, R has to be phenyl or trimethylsilyl group. Simple alkyl-substituted alkynes fail to give the corresponding tandem product. In order to remedy this situation, alkynylzinc reagent is used to replace alkynylstannanes and tandem coupling products are thus obtained in satisfactory yield [159]. 

Tandem coupling of chlorotrimethylsilane, a, -enones, terminal or internal alkynes and dimethyl zinc in the presence of catalytic amounts of Ni(acac)2 and PhjP affords the corresponding three-component coupling products [160]. 

Attempts to use chiral oxazolines as auxiliary for the asymmetric induction of this reaction have been only partially successful [161], 

Intramolecular cyclization of alkynyl enones by means of Ni(COD)2 catalyst in the presence of dimethyl zinc gives the corresponding cyclic product. When Bu2Zn is used in the presence of PhjP, reductive cyclization occurs to give the corresponding reduced product [162-164]. Cyclic enones interestingly give the spiro products in satisfactory yields. 

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Several reviews have been devoted to the subject of, among other cycloaddition reactions, (2 + 2)-cycloaddition reactions to enones. Within these articles the additions of alkynes has been dealt with. Specifically, a short review has discussed the cycloaddition reactions of enones with alkynes. ... 

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