A-Keto acylsilanes

Yagi and coworkers84 reported the preparation of ce-keto acylsilanes in a one-pot operation. To a mixture of dibromomethane and tc/t-butyldimethylsilyl chloride in THF, LDA was added at — 78 °C, forming /< /7-bu tyldi methyl silyldibromomcthy (lithium, 89. To the resulting mixture 4-methoxybenzonitrile was added. Quenching with 1 M HC1 afforded a-keto acylsilane, 90, in 55% yield (Scheme 30). 

CL-Keioacylsilanes. Reaction of (Z)-vinylsilanes (1), with OSO4 and tri-methylamine oxide gives the cw-l,2-diols (2) in moderate yield. These can be oxidized by DMSO/oxalyl chloride to a-keto acylsilanes (3, 40-55% yield). 

Yagi, K., Tsuritani, T., Takami, K., Shinokubo, H., Oshima, K. Reaction of Silyidihalomethyllithiums with Nitriles Formation of a-Keto Acylsilanes via Azirines and 1,3-Rearrangement of Silyl Group from C to N. J. Am. Chem. Soc. 2004,126, 8618-8619. 

Epoxidation of f-butyldimethylsilyl-l-(ethoxyethoxy)allene (6) with /n-chloroperbenzoic acid leads to an a-keto acylsilane, presumably through an allene oxide intermediate (eq 6). Deprotonation of (6) at C-3 and trapping of the anion with selenium, followed by iodomethane, produces an aUenyl selenide. The reaction of this material with peracid follows a different course, leading to an acetylenic acylsilane, presumably via [2,3]-sigmatropic rearrangement of an allenyl selenide (eq 6) ... 

The Swern oxidation proceeds rapidly at low temperatures and thus can be employed for the preparation of a-keto aldehydes and acylsilanes, which are hyperactive carbonyl compounds and prone to hydration, polymerization, and air oxidation. ... 

Alkylation of the Uthium salt of TMSCHN2 (TMSC(Li)N2) gives a -trimethylsLlyl diazoalkanes which are useful for the preparation of vinylsilanes and acylsilanes. Decomposition of a-tri-methylsilyl diazoalkanes in the presence of a catalytic amount of Copper(I) Chloride gives mainly ( )-vinylsilanes (eq 12), while replacement of CuCl with rhodium(II) pivalate affords (Z)-vinylsilanes as the major products (eq 12). Oxidation of a-trimethylsilyl diazoalkanes with m-Chloroperbenzoic Acid in a two-phase system of benzene and phosphate buffer (pH 7.6) affords acylsilanes (a-keto silanes) (eq 12). ... 

Johnson s group developed a catalytic asymmetric cyanation/1,2-Brook rearrangement/C-acylation of acylsilanes with cyanoformates (Scheme 19.14). In the presence of (i ,/ )-(salen)Al 19, the corresponding cyanohydrin trimethylsilyl ethers of a-keto esters were obtained in moderate to good enantioselectivities (61-82% enantiomeric excess). Access to chiral (silyloxy)nitrile anions is facilitated by metal cyanide-promoted Brook rearrangement reaction of acylsilanes. 

Acylsilanes are yet another class of valuable synthetic intermediates, and new methods for their synthesis are always welcome. In the first of several examples reported this year, the silyl allene (168) has been used as a common intermediate for the preparation of a diverse range of acylsilanes with a,p-olefinic, a,p-acetylenic, and a-keto substituents. Alkyl-substituted acylsilanes are now available via a high-yielding process in which an acyl-lithium (generated in situ from an alkyl-lithium and CO) is trapped by MeaSiCl. Cyclic acylsilanes have been prepared from cyclic vinylsilanes by way of an epoxidation-reductive ringopening-oxidation sequence. ... 

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