Ynolates metal complexes

Ynolate metal complexes can be selectively alkylated or acylated to form the corresponding ynol ether complexes 33 (equation 22) or ynol ester complexes 34 (equation 23). ... 

Compared with metal enolates, there have been very few reports on the direct structural analysis and theoretical studies of ynolates. An X-ray crystal structure of a vanadium complex of lithium ynolate with a porphyrinogen ligand (56) is reported. This metal complex was incidentally formed from VCl3(THF)3 with tetralithium salt of the octaethyl-porphyrinogen ligand. In this complex, the lithium cation seems to interact with the 7T-electrons of the ynolate. The four atoms of the ynolate group in 56 are not collinear due to a partial sp character of the group in this complex. 

There has been only a few reports on reactions of small rings with metal ynolates. Oxiranes are much less electrophilic than carbonyls and sometimes need activation by Lewis acids or Lewis-acidic organometals. The lithium-trimethylaluminum ate complex of i/ZyZ-substituted ynolate 105 reacts with the oxirane 106 to give the y-lactone 107 (equation 44), while lithium silyl-substituted ynolates are inert to oxiranes. There have been no reports using carbon-substituted metal ynolates. 

Although the Michael addition of metal ynolates to a,/ -unsaturated carbonyl compounds is expected to give six-membered cycloadducts, 1,2-addition to carbonyl groups usually precedes 1,4-addition. The cycloaddition of the lithium-aluminum ate complex of silyl-substimted ynolate 112 with ethyl benzylideneacetoacetate (113), which is doubly activated by the ester and keto functions, gives the y-lactone 114 via a [4 4- 2] type cycloaddition (equation 46). Diethyl benzylidenemalonate (115) affords the uncyclized ketene 116 by reaction with 112 (equation 47). This could be taken as evidence for a stepwise mechanism for equation 46. ... 

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