Ketene disilyl acetals

Monoalkyl ethers of (R,R) 1,2-bis[3,5-bis(trifluoromethyl)phenyl]ethanediol, 24, have been examined for the enantioselective protonation of silyl enol ethers and ketene disilyl acetals in the presence of SnCU (Scheme 12.21) [25]. The corresponding ketones and carboxylic acids have been isolated in quantitative yield. High enantioselectivities have been observed for the protonation of trimethylsilyl enol ethers derived from aromatic ketones and ketene bis(trimethylsilyl)acetals derived from 2-arylalkanoic acids. 

S, 0-acetals, and carboxylic acid silyl ester derivs. from ketene disilyl acetals, s. 

The latter mode of activation, in which a charged tetraaminophosphonium salt acts as a Bronsted acid, was realized by the same research group in 2009. Enanti-oselective aza-Michael reaction of 2,4-dimethoxyaniline with nitroalkenes afforded the conjugate addition products in excellent yields and high enantiomeric excesses (Scheme 10.70) [173, 174]. Similarly, chiral diaminooxaphosphonium salts have been used as Br0nsted acids in the asymmetric protonation reactions of ketene disilyl acetals [175]. 

Nakamura S, Kaneeda M, Ishihara K, Yamamoto H. Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Brpnsted acids reaction scope and mechanistic insights. J. Am. Chem. Soc. 2000 122 8120-8130. 

Uraguchi D, Kinoshita N, Ooi T. Catalytic asymmetric protonation of a-amino acid-derived ketene disilyl acetals using P-spiro diaminodioxaphosphonium barfates as chiral proton. J. Am. Chem. Soc. 2010 132 12240-12242. 

The question of regiochemistry does not arise in the case of diesters. Diethyl succinate has been converted to the disilyl ketene acetal (59) in good yield. A number of glutarate esters (60) have been similarly transformed to (61). ... 

C,6H23CH(R)C02H Disilyl ketene acetal, MeLi (32) 45 63... 

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