Carbonyl compounds ynolates

A naphthalene-catalyzed (<10%) lithiation of a,a-dibromo esters 152 in THF at —78°C was used to generate ester dianions 153, which by warming at 0°C gave lithium ynolates 154. These intermediates were trapped by carbonyl compounds, for instance benzophenone, to give, after final hydrolysis with water, a,/3-unsaturated acids 155 (Scheme 55)" ... 

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. ... 

Homer-Wadsworth-Emmons reactions encounter serious problems of reactivity, stereoselectivity, and generality when used to form tetrasubstituted olefins. Most studies on the synthesis of tetrasubstituted olefins exploit alternative routes based on carbometalation of alkynes [17-19]. However, these processes have difficulties associated with the regioselectivity of the initial carbometalation and with reactivity during the final coupling. Here we describe stereoselective s3mtheses of tetrasubstituted olefins, via the olefination of carbonyl compounds with ynolates, as well as some synthetic applications [20,21]. 

Stereoselective synthesis of tetrasubstituted alkenes remains a challenging task. A unique solution to this problem is to use torquoselectivity-controlled oletina-tion of carbonyl compounds with ynolates, which is summarized in Chapter 1. In general, the stereoselective synthesis of Z-alkenes, which are thermodynamically less favorable, is more difficult than the synthesis of corresponding -isomers. In Chapter 2, various methods for stereoselective synthesis of Z-alkenes are reviewed. Finally, the C=C double bond formation through catalytic carbene transformation has recently emerged as a new approach toward olefin synthesis. Two chapters covering olefin synthesis based on catalytic carbene transformations are included (Chapter 5 and Chapter 8). 

Review Shindo M, Mori S. Torquoselective olefination of carbonyl compounds with ynolates highly efficient stereoselective synthesis of tetrasubstituted alkenes. Synlett 2008 2231-2243. 

Lithium trimethylsilylethynolate. Carbonylation of the lithium compound with CO IS accompanied by Nj elimination and bonding reorganization. The ynolate species can be nansformed into bissilyl ketenes and other interesting compounds. 

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