Ynolate anions

ETHYL 1 -NAPHTHYLACETATE ESTER HOMOLOGATION VIA YNOLATE ANIONS... 

Rajarathnam E. Reddy and Conrad J. Kowalski 146 ETHYL 1 -NAPHTHYLACETATE ESTER HOMOLOGATION VIA YNOLATE ANIONS... 

A highly Z-selective olefination of a-oxy and a-amino ketones via ynolate anions has been reported (Scheme 9).43 The stereocontrol mechanism has been explained by (g) orbital interactions between the s orbital of the breaking C-O bond or n orbital of the enolate and the s orbital of the C-O or C-N bonds of the substituent in the ring opening of the /I-lactone enolate intermediates, and/or the chelation to lithium. 

Ynolate anions react with acylsilanes at low temperature to give P-lactones 48 in good yields. When the reaction is conducted at room temperature the isolated product is a (1-silyl-a,p-unsaturated ester via a P-lactone enolate intermediate <02JACS6840>. 

The ESI mass fragment ion spectra of the monomethyl glutarate anion (58) shows formation of ynolate anions (equation 23). ... 

Ester Homologation via Ynolate Anions Methyl 3-Cyc1ohexeny1acetate C. J. Kowalski and S. Sakdarat, Synthetic Chemistry Department,... 

Ynolate anions as equivalents of ketenyl anions and their transformations into /Mactones and /1-lactams 00YZ1233. 

According to its structure, which can be represented by two resonance contributors (equation 11), an ynolate anion has two nucleophilic centers. In principle, attack of an electrophilic reagent on the oxygen atom of an ynolate anion leads to the formation of an ynol ether or ester, whereas C-attack gives a ketene molecule. 

Both types of reactivity of ynolate anion have been reported in the literature. The O-attack is typical for the reactions of lithium ynolates with trialkylchlorosilanes b24,25 dialkyIchlorophosphates. Lithium ynolates, generated as shown in equations 5-10, react with sterically hindered trialkylchlorosilanes in THF affording silyl ynol ethers as primary products (equation 12). However, in some cases the silyl ynol ethers are unstable at room temperature and isomerization to the more stable ketenes, or decomposition, occurs The ketene rearrangement usually occurs in reactions of lithium alkynolates with methyl substituted silyl chlorides a typical example of such a rearrangement is represented by reaction 13 ". ... 

R Ester Homologation via Ynolate Anions Methyl 3-Cyclohexenylacetate... 

Formation of Silyl Ynol Ethers. Esters can also be transformed into triisopropylsilyl 3mol ethers. The ester is first converted to the ynolate anion, followed by treatment with TIPSCl to... 

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