Enol ethers disilyl

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. 

In a series of papers West and coworkers described the reactions of disilene 9 with several epoxides to give the disilyl enol ethers 125, the five-membered ring compounds 126 — the formal insertion products, as well as the products of epoxide deoxygenation, namely alkenes and the disilaoxirane 62 (equation 29)80,83,124 125. 

Disilylation of enones.1 In the presence of Pd[P(C6H5),]4, this disilane undergoes 1,4-addition to a,p-enones to give -y-(phenyldichlorosilyl) silyl enol ethers, which can be converted into lithium enolates by exchange with methyllithium. The reaction can provide 3-hydroxy ketones. The Michael addition is enantioselective when catalyzed by Cl2Pd[( + )-BINAP] (12, 53-57). 

The synthetic technique is summarized in Scheme 3. Reaction of chaparrin (41b) with tert-butyldimethylsilyl chloride 11) afforded the crystalline disilyl derivative (93). The latter was obtained in better yield by silylation of (41b) with tert-butyldimethylsilyl enol ether of pentane-2,4-dione 105). The hydroxyl function at C-1 of (93) was effectively protected using trimethylsilyl triflate to afford the trisilyl lactone (94) which upon treatment with lithium diisopropylamide (LDA) and subsequent exposure to MoOs-pyridine-HMPA (M0O5PH) 104) gave the required 15-hydroxy lactone (95). Treatment of the latter with isovaleryl chloride afforded the crystalline ester (96) which was selectively desilylated to (97). Oxidation of the free allylic hydroxyl and complete desilylation of the resulting disilyl enone with tetrabutylammonium fluoride (BU4NF) afforded the natural cytotoxic quassinoid castelanone (34). 

Alkyl and acylsilanes Tetraalkylsilanes are inert to the carbonyl coupling reaction conditions, as shown by the syntheses of 43 and 44 [61, 62]. Despite their dose similarity to sterically hindered ketones, McMurry reactions of acylsilanes are limited to the preparation of the 1,2-disilylated stilbenes 45 (R = H, Br or OMe) silyl enol ethers are also obtained as by-products, resulting from silatropic migration [63], No such coupling of aliphatic acylsilanes has yet been reported. 

Tetramesityldisilene adds to either cis- or treais-stilbaie oxide to give an E/Z mixture disilyl enol ethers, a 3-oxa-l,2-disilacyclq >entane and a 3-oxa-l,2-disilacyclo nDpane 7. 

Hydrosilylation of vinylmethylsilane with chlorosilanes has been reported using catalytic amounts of tetracarbonyl(Ti -trimethylsilylethene)iron. A product mixture consisting of isomeric disilylethanes, monosilylethane, and disilylated ethene was obtained. Acrolein diethyl acetal can be hydrosilylated with triethylsilane in the presence of 1 mol% pentacarbonyliron to give the corresponding Markovnikov product (Scheme 4-335). Allyl alcohols afford a mixture of the allyl silyl ether and the alltyl silyl ether, whereas acrolein leads to a mixture of cis and trans silyl enol ethers. ... 

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. 

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