Acylsilanes preparation

Substituted aroyl- and heteroaroyltrimethylsilanes (acylsilanes) are prepared by the coupling of an aroyl chloride with (Me3Si)2 without decarbonylation, and this chemistry is treated in Section 1.2[629], Under certain conditions, aroyl chlorides react with disilanes after decarbonylation. Thus the reaction of aroyl chlorides with disilane via decarbonylation is a good preparative method for aromatic silicon compounds. As an interesting application, trimel-litic anhydride chloride (764) reacts with dichlorotetramethyidisilane to afford 4-chlorodimethylsilylphthalic anhydride (765), which is converted into 766 and used for polymerization[630]. When the reaction is carried out in a non-polar solvent, biphthalic anhydride (767) is formed[631]. Benzylchlorodimethylsilane (768) is obtained by the coupling of benzyl chloride with dichlorotetramethyl-disilane[632,633]. 

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

The unusual l-sila-l,2-diol (CH2=CH)CH(OH)SiPh2OH, prepared by hydrolysis of the acylsilane (CH2=CH)C(0)SiHPh2, has a structure comprising hydrogen-bonded double chains as shown in Fig. 9. Only COH - HOSi hydrogen bonds are present, with the bonds between the chains being shorter than those that build up the chain, 2.666 and 2.739 A, respectively (131, 210). 

In view of the evident reactivity of the Brook-type silenes toward carbonyl compounds and the fact that these silenes were prepared by the photolysis of acylsilanes, it is natural to ask why the silenes apparently did not react with their acylsilane precursors. This question has been answered recently. On the one hand, as shown in Scheme 19, the silene Ph2Si=C(OSiMe3)Ad apparently did add in a [2 + 2] manner to its acylsi-... 

Preparative electrochemical oxidations of acylsilanes proceed smoothly in methanol in an undivided cell equipped with carbon rod electrodes to give the corresponding methyl esters. The C-Si bond is cleaved and methanol is introduced at the carbonyl carbon (Scheme 22) [16]. 

The biomimetic cationic domino cyclization of an acyclic unsaturated substrate to give the tetracyclic scaffold of triterpenes and steroids is intensively described in the literature.1121 The concept has recently been used by Corey et al. to prepare enanti-opure (+)-dammarenediol II 18 in an exceptional short way.1131 The synthesis demonstrates the power of the combination of cation-olefin polyannulation with the aldol cyclization for tetraannulation (scheme 4). Successive treatment of the acylsilane 13 with 2-propenyllithium 14 and the iodoalkane 15 efficiently yidds the epoxytriene 16. The Lewis acid... 

Allenyl silyl ethers 40 have also been prepared by the reaction of 2-lithiofurans 38 with acylsilanes 39 via the Brook isomerization (equation 15) . 

Even the starting acylsilane 39 can be easily prepared via a Brook isomerization by the reaction of silylmethyllithium 41 with carbon monoxide " °. Initially, the reaction gives the corresponding unstable acyllithium 42 which underwent the Brook isomerization affording the stable lithium enolate (equation 16). 

Acylsilanes.1 The anion (1, prepared with BuLi) of trimethylsilyldiazomethane reacts with alkyl halides to form an a-trimethylsilyldiazoalkane (2), which is... 

AEM-Disilylenamines of acylsilanes, which are excellent precursors for a-(trimethylsilyl)alkylamine, can be prepared electrochemically using a similar procedure (equation 92)116. 

Enantioselective reduction of the prochiral cyclic acylsilane 42 with growing cells of the yeast Kloeckera corticis (ATCC 20109) yielded the optically active reduction product (R)-43 (Scheme 8)53. On a preparative scale, the l-silacyclohexan-2-ol (R)-43 was isolated in 60% yield with an enantiomeric purity of 92% ee. Repeated recrystallization of the biotransformation product from n-hexane raised the enantiomeric purity to 99% ee. 

Scheme 15)62. After terminating the reaction at a conversion of 38% (relative to total amount of substrate rac-78), the product (S)-43 was separated from the nonreacted substrate by column chromatography on silica gel and isolated on a preparative scale in 71% yield (relative to total amount of converted rac-78) with an enantiomeric purity of 95% ee. Recrystallization led to an improvement of the enantiomeric purity by up to >98% ee. The biotransformation product (S)-43 is the antipode of compound (/ )-43 which was obtained by enantioselective microbial reduction of the acylsilane 42 (see Scheme 8)53. The nonreacted substrate (/ )-78 was isolated in 81% yield (relative to total amount of nonconverted rac-78) with an enantiomeric purity of 57% ee. For further enantioselective enzymatic hydrolyses of racemic organosilicon esters, with the carbon atom as the center of chirality, see References 63 and 64. 

Acyl(phosphido) complexes, with Pt(II), 8, 458 Acyl radicals, via selenium precursors, 9, 477 Acylsilanes, applications, 9, 319 Acylstannanes, preparation, 3, 822-823 l-Adamantyl-2-pyridyl amido complexes, with Zr(IV), 4, 782 Adaptive quantum control, for selective bond cleavage, 1, 247 Addition reactions... 

Enamines have been prepared through reductive-trimethylsilylation of cyanohydrins as precursors of acylsilanes.la 192 As indicated above, these enamines are also excellent starting materials for synthesizing RSMAs via reduction of the corresponding iminium chlorides with sodium borohydride.la,lb... 

Four-membered rings containing three silicon atoms (compounds of type 2) were prepared by reaction of acylsilane with Et3GeLi in THF <1999JA8118> or by thermal rearrangement of trans-silane 32 <2006AGE6371>. 

The sulfur analogues of acylsilanes have been prepared by treatment with H2S or Lawesson s reagent [79-81]. 

Lithium bis(trimethylsilyl)cuprate.xl This cuprate, prepared from (CH3),SiLi and CuCN, converts acyl chlorides into acylsilanes in moderate to high yield. 

Photolysis of acylsilanes produces siloxysubstituted carbenes, which could be trapped by an excess of electrondeficient olefins. This route to the resulting alkyl 2-siloxycyclopropanecarboxylates seems not to be of preparative value, however 67). 

Indium-mediated allylation of trialkyl(difluoroacetyl)silane 70 in aqueous media gives homoallylic alcohol 71 exclusively (Scheme 60). Both water and THF are essential for the allylation reaction. It is worth noting that homoallylic alcohol 71 is formed exclusively under these reaction conditions. On the contrary, enol silyl ether 72 is a major product of the fluorinated acylsilanes reaction with other organometallic compounds than indium via a Brook rearrangement and defluorination. Indium-mediated allylsilylation of carbonyl compounds provides a facile route to 2-(hydroxyethyl)allylsilanes. The allene homologs are similarly prepared (Scheme 61).244,244a... 

The chemistry of thiolactones is particularly interesting because of the biological activity associated with a number of these derivatives.59 More recently, a method has been pursued51 for the preparation of silylated unsaturated thiolactones 56 having a five- to ten-membered ring (Scheme 37). a-Carboxy acylsilanes 57,... 

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). 

S-Substituted a-lithiated silyl enol ether 557 has been prepared by reductive lithia-tion of vinyl tellurides834 and sulfides835,836 with lithium 1 -(dimethylamino)naphthalenide (LDMAN). This intermediate 557 gave, after inverse Brook rearrangement, the enolate 558 and after hydrolysis the corresponding acylsilane (Scheme 151). 

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