Vinylation metal enolates

Direct treatment of TIPS enol ethers of a variety of cyclic and acyclic ketones with the strong-base combination of n-BuLi/KO-t-Bu leads to /3-ketosilanes (2) after aqueous work-up. In contrast with the earlier method, this rearrangement appears to proceed through allylic, rather than vinylic, metallation, since enol ethers lacking an allylic a-proton are unreactive. 

With conjugated enone substrates, the alkoxymetallation leads to the formation of a metal enolate that can undergo a facile protonation to accomplish the hydroalkoxylation. Following this mechanism, various /3-alkoxyketones were obtained in good yields by the addition of primary and secondary alcohols to methyl vinyl ketone under cationic Pd(n) catalysis.443 Similarly, [Rh(COD)(OMe)]2 was found to catalyze the hydroalkoxylation of both methyl vinyl ketone and phenyl vinyl ketone (Equation (121)).444... 

J. E. Baldwin, G. A. Hofle, and O. W. Lever, Jr., a-Methoxy vinyl lithium and related metalaled enol ethers. Practical reagents for nucleophilic acylation, J. Am. Chem. Soc. 96 7125 (1974). 

But this strategy is doomed too as the allylic bromide will almost certainly react at its less hindered end on the vinyl group. However, we might choose the alternative branchpoint disconnection 38a and consider conjugate addition of some vinyl-metal (copper ) derivative to the enone 41 that could be made by some aldol process from the ketone 42 and an enol(ate) of acetone 43. 

One of the most important contributions in metal enolate catalysis is the conjugate addition of arylboronic acids (115) to vinyl ketone derivatives (116) to give the corresponding aryl ketones (117) (equation number of advances have recently... 

Therefore, our first idea was to 0-acylate simple enolates with phosgene. In a first course of attempts, we investigated the reaction of phosgene with alkaline metals enolates. For example we prepared lithium enolate of acetaldehyde through cleavage of tetrahydrofuran by n- butylllthium (Ref. 116) and reacted with phosgene under various conditions. Unfortunately, no trace of vinyl chloroformate was found in all experiments performed [Scheme 90]. 

Addition of vinyl metals to aldehydes and ketones (chapter 16) also allows control over stereochemistry. The stereospecific vinyl anion equivalent 24 is one we made in chapter 16 by the Shapiro reaction. We repeat this scheme because it uses prenylation of a hydrazone aza-enolate to make the starting material for the vinyl-tin compound 25. 

Alkyl enol ethers can be conveniently prepared by the alkylation of a-methoxyvinyllithium and related metallated enol ethers. In a typical example, methyl vinyl ether (1) is converted by r-butyllithium to give a-methoxyvinyllithium (2). Reaction of (2) with octyl iodide gives the enol ether (3). Metallation of methyl propenyl ether (4) and methyl allenyl ether (5) can be similarly executed. ... 

This metalated enol ether is prepared by reaction of f-butyllithium with methyl vinyl ether in THF at -65° (exothermic reaction). A yellow precipitate of a complex of r-butyllithium and THF forms, which dissolves at -5 to 0° to give a colorless solution of the reagent (1). This substance is the synthetic equivalent O... 

Carbon-carbon bond formation by using metal enolates as synthons in organic chemistry and the protonation, alkylation, arylation, and vinylation of enolates have been reviewed. " The stereoselective carbon-carbon formation of bond through Mannich reaction has been detailed according to the type of Mannich base produced. Phosphine-catalysed asymmetric additions of malonate esters to y-substituted allenoates and aUenamides have been reported. ... 

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