Trimethylsilyl benzoates

Diels-Alder reactions of 1,3-cyclohexadienes and 3-(trimethylsilyl)propynoates. A new synthesis of orf/7o-(trimethylsilyl)benzoate esters [149]... 

Finally, esters, for example methyl benzoate, are readily transesterified by excess alcohol, for example ethanol, in the presence of trimefhylsilyl iodide 17, in boiling chloroform, to give, via trimethylsilyl benzoate, the desired ethyl benzoate in 98% yield [117]. 

The carbonyl group of methyl benzoate condenses with Na-HMDS 486 to give methoxytrimethylsilane 13a and 51% yield of N,0-bis(trimethylsilyl)benzamide 296 [99], which is also accessible by silylation of benzamide with TCS 14/triethyla-mine. Benzamide or N-silylated benzamide, however, are converted by Na-HMDS 486 in benzene and subsequent quenching with MesSiCl 14 into 34% N,0-bis(trimethylsilyl)benzamide 296, 24% crystalline N-silylated benzamidine 524, and HMDSO 7 [99] (Scheme 5.32). 

Amides such as DMF or ureas such as N,N-tetramethylurea react with bis(trimethylsilyl)selenide 604 in the presence of BF3-OEt2 to give selenoamides, for example 617, or selenoureas whereas esters such as n-butyl benzoate react with 604 in the presence of Bp3-Et20 and 2,3-dimethylbutadiene to give 619 via 618 [157]. On heating with P4Sio/sulfur and hexamethyldisiloxane 7 y9-ketoesters such as ethyl acetoacetate are converted to 3H-l,2-dithiole-3-thiones such as 620 in high yields [158] (Scheme 5.51 cf. also Section 8.6). 

Trimethylsilyl iodide 17, which can be generated in situ by reaction of trimethyl-silyl chloride (TCS) 14 with Nal in acetonitrile [1], converts alcohols 11, in high yields at room temperature, into their iodides 773a, HI, and hexamethyldisiloxane (HMDSO) 7 [1-8, 12]. Likewise esters such as benzyl benzoate are cleaved by Me3SiCl 14/NaI in acetonitrile under reflux [Ij. Reactions of alcohols 11 with trimethylsilyl bromide 16 in chloroform or, for in situ synthesis of 16 from liBr and TCS 14 in acetonitrile and with HMDS 2 and pyridinium bromide perbromide, proceed only on heating in acetonitrile or chloroform to give the bromides 773 b in nearly quantitative yield [3, 8, 12] (Scheme 6.1). 

Me3SiCl 14 (40 mmol) is added with stirring to a solution of 20 mmol benTyl benzoate and 40 mmol Nal in 20 mb abs. acetonitrile. The reaction mixture is then heated under reflux for 4 h, cooled to room temperature, and 50 mb H2O is added to saponify the trimethylsilyl benzoate. The reaction mixture is then taken up in 2 X 50 mb ether, which is washed successively with H2O and aqueous thiosulfate solution to remove inorganic salts and iodine. The benzoic acid is then extracted with 2 X 15 mb aqueous 15% NaHC03 solution, leaving benzyl iodide and traces of unreacted benzyl benzoate in the ether layer. On acidification of the aqueous NaHC03 extract 80% benzoic acid is recovered [1] (Scheme 6.17). 

Excess Peterson reagent 1606 a reacts with methyl benzoate, via the intermediates 1609 and 1610, to give, on work-up, some a-trimethylsilylacetophenone 1609 and 49% phenylallylsilane 1611 [15], whereas with 1606a ethyl cyclohexanecarboxylate affords only the a-trimethylsilyl-ketone 1612 [16, 17] (Scheme 10.6). 

A solution of n-Bubi in hexane (2.5 M, 980 b, 2.2 mmol) is added dropwise to a mixture of N-trimethylsilyl-o-toluidine 1602 (200 mg, 1.12 mmol) in 10 mb dry hexane. The resulting yellow solution is heated under reflux for 6 h and then left to cool to room temperature. The dianion 1603 is then added via a caimula to a precooled solution of ethyl benzoate (176 mg, 1.17 mmol) in 4 mb THF. The reaction mixture is then warmed to room temperature and partitioned between 10 mb each of ether and ice-water. The aqueous layer is extracted with ether (4x10 mb) and the combined organic extracts are washed with 10 mb brine, dried (MgS04), and concentrated in vacuo. Flash chromatography with 95 5 hexane-EtOAc gives 140 mg (65%) 2-phenylindole 1605, m.p. 182-184°C [12] (Scheme 10.24). 

The use of ester and formyl groups for this reaction is also possible. The reaction of methyl benzoates with olefins proceeds when the benzoates have electron-withdrawing substituents such as trifluoromethyl, cyano, and ester groups (Equation (8)).5,5a In the case of aldehydes, the reaction requires sterically hindered substituents such as tert-butyl and trimethylsilyl groups.6... 

Scheme 3.37 describes gas-phase generation of m-benzyne anion (the distonic anion-biradical) from m-bis(trimethylsilyl) benzene (Wenthold et al. 1994, 1996 Wenthold and Squires 1998). The same anion-biradical is formed from isophthalic acid under the same conditions (Reed et al. 2000). Particularly, the reaction of m-bis(trimethylsilyl) benzene with fluoride ion, followed by treatment of the formed trimethylsilyl phenyl anion with fluorine in helium, produces the anion-biradical mentioned. The latter is transformed into the corresponding nitro benzoate anion through the addition of CO2 and NO2 (Scheme 3.37). 

Mohammadpoor-Baltork I, Khosropour AR (2002) Efficient and selective conversion of trimethylsilyl and tetrahydropyranyl ethers to their corresponding acetates and benzoates catalyzed by bismuth(III) salts. Monatsh Chem 133 189-193... 

For the mono-C-glycosylphenol, the commercially available 2,4,6-trihydroxyacetophe-none was chosen and selectively methylated at C-2 and C-4. The partially protected phenol was glycosylated with the C-benzyl-protected glucosyl trichloroacetimidate in the presence of trimethylsilyl triflate as promoter to give directly a C-(benzyl protected)glycosylphenol. The unprotected hydroxyl group of this compound was converted with benzoyl chloride into a fully protected C-glycoside phenol. Treatment of the benzoate derivative with sodium hydroxide in... 

Trimethylsilyl benzoates react with xenon difluoride in dichloromethane or hexafluorobenzene to give rearranged products, i.e. aryl fluoroformates.74... 

Reduction of derivatives of ally lie alcohols. Nickel boride can effect reduction of allylic alcohols to alkenes, but yields are generally improved by reduction of the acetates, benzoates, or trifluoroacetates.1 Reduction of allylic benzyl ethers to alkenes is effected in higher yield with Raney nickel. Methyl ethers are not reduced by either reagent. The trimethylsilyl ethers of allylic alcohols are reduced to alkenes by nickel boride in diglyme.2... 

Photolysis of benzoyltrimethylsilane at 10 K in the absence of oxygen showed no changes in the IR spectrum of the matrix after several hours. In the presence of oxygen a variety of products was identified including trimethylsilyl benzoate and the main product trimethylsilyl perbenzoate. 

Elimination of iodobenzene alone from 2-phenyliodonio benzoate leads to generation of another transient 1,4-dipole which was trapped by phosphaalkynes [55], A new precursor, 2-trimethylsilyl-diphenyliodonium triflate, obtained from 1,2-bis-trimethylsilylbenzene, (diacetoxyiodo)benzene and triflic acid, permitted the generation of benzyne with tetrabutylammonium fluoride, at room temperature [56] ... 

Calibration Standards Prepare four HQ calibration standards as follows Add 0.50, 1.00, 2.00, and 3.00 mL of HQ Stock Solution into separate 10-mL volumetric flasks, then add 2.00 mL of Methyl Benzoate Stock Solution (internal standard) to each, dilute to volume with pyridine, and mix. In the same manner, prepare four DTBHQ Stock Solution calibration standards. Prepare the trimethylsilyl derivative of each standard as follows Add 9 drops of calibration standard to a 2-mL serum vial, cap the vial, evacuate with a 50-mL gas syringe, add 250 p,L of A.O-bistrimethylsilylacetamide, and heat at about 80° for 10 min. 

Sample Preparation Transfer about 1 g of sample, accurately weighed, into a 10-mL volumetric flask, add 2.00 mL of Methyl Benzoate Stock Solution, dilute to volume with pyridine, and mix. Prepare a trimethylsilyl derivative as described under Calibration Standards (above). 

Through a rather complicated sequence of meanwhile fully understood reaction steps ethyl benzoate and lithium bis(trimethylsilyl)phosphanide form tris(l,2-dimethoxyethane-0,0 )-lithium 3-phenyl-l,3-bis(trimethylsilyl)-l,2-diphosphapropenide and 3,5-diphenyl-l,2-bis(tri-methylsilyl)-l,2,4-triphospholide. X-ray structure determinations on orange or green, metallically lustrous, crystals show the compoxmds to be ionic in the solid and to contain a 1,2-diphosphaallyl and a 2-phosphaallyl anion, respectively. Dark red tetrakis(tetra-... 

The first step - a 1,2-diphosphaallyl anion [49] In contrast to the syntheses of dimeric l-(l,2-dimethoxyethane-0,0 )lithoxyaikylidenephosphanes from ethyl formate or 2,4,6-trimethyl-benzoyl chloride and (l,2-dimethoxyethane-0,0 )lithimn phosphanide already mentioned (Eq. 13), the reaction of ethyl benzoate with lithium bis(trimethylsilyl)phosphanide at about 0 °C in... 

In order to understand the formation of compounds now being discussed one has to realize that tris(trimethylsilyl)phosphane originating in the desilylation of [l-(trimethylsiloxy)benzylidene]-trimethylsilylphosphane (Scheme 1) reacts slowly with lithium ethanolate to give lithium bis(trimethylsilyl)phosphanide again (Eq. 13). This compound must then be considered a continuous source for the phosphaalkyne H5Q-C P, provided that a sufficient amoimt of ethyl benzoate is present in solution. 

A 2-phosphaallyl anion as part of a five membered heterocycle [27, 35] When in the already discussed reaction between ethyl benzoate and lithium bis(trimethylsilyl)phosphanide the molar ratio of the educts is changed finally from 1 3 to 1 1, dark green, metallically lustrous, air sensitive crystals of... 

In the first example, nitration of the benzoate (140) with nitric acid affords the nitro derivative. Hydrogenation converts this to the anthranilate (141). In one of the standard conditions for forming quinazolones, that intermediate is then treated with ammonium formate to yield the heterocycle (142). Reaction of 142 with phosphorus oxychloride leads to the corresponding enol chloride (143). Condensation of 143 with m-iodoaniline (144) leads to displacement of chlorine and consequent formation of the aminoquinazoline (145). Reaction with the trimethylsilyl derivative of acetylene in the presence of tetrakis-triphenylphosphine palladium leads to replacement of iodine by the acetylide. Tributylammonium fluoride then removes the silyl protecting group to afford the kinase inhibitor erlotinib (146). ... 

The acylation of the pinacol derivative of dihydTOxy[lithio(trimethylsilyl)methyl]borane with methyl benzoate has been recoided, No details were given due to difficulties in the isolation of the products. 

Reaction of enol silyl ethers with lead tetrabenzoate followed by treatment with triethylammonium fluoride leads to the a-benzoyloxyketones. In both cases, the sequence involves bisoxygenation of the double bond followed by hydrolysis. a-Acetoxylation is also possible, but the benzoate is the reagent of choice for that system. i In the cyclohexanone series, reaction of lead tetraacetate with cyclohexanone trimethylsilyl enol ether afforded also a-acetoxycyclohexanone after hydrolysis." When the same reaction was performed on the triethyltin enol ether, the main product was now a-acetoxycyclohexanone with a small amount of dimeric product. This latter result could be explained by a transmetallation followed by ligand coupling, in the major pathway. 

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