Silanes carboxylic acid silyl ester

Carboxylic acid silyl esters from silanes... 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

Trimethylsilyl ethers and esters.i The reaction of alcohols and allyltrimethyl-silane in acetonitrile with TsOH as catalyst (70 80°, 1 3 hours) results in trimethyl-silyl ethers in 85-95% yield with elimination of propene. The same reaction with carboxylic acids results in trimclhylsilyl esters. Phenols do not undergo this reaction. 

Silane reacts with methanol to give the alkoxysUanes (MeO) SiH4 (n = 2, 3, 4) and with higher alcohols in the presence ofbase to give tetraalkoxysilanes (equation 8). This type of reaction is, however, rarely carried out as the alkoxysi-lanes produced are more conveniently prepared from alcohols and SiCU (which is more readily available than SiELi and much more easily handled). Similarly, silyl esters, Si(OCOR)4, are also usually prepared from polyhalogenosUanes rather than from silane and a carboxylic acid. 

Summary Rhodium-siloxide dimer [ (diene)Rh(jr-OSiMe3) 2] (I) appeared to be an active catalyst (even at room temperature) of the hydrosilylation of allyl ethers, CH2=CHCH20R (R = CH2(I HCH20, C4H9, Ph, CH2Ph, (CH2CH20)7H) by triethoxysilane and methylbis(trimethylsiloxy)silane as well as of allyl esters of selected carboxylic acids, i.e. allyl acetate and allyl butyrate, to yield the usual hydrosilylation products accompanied (in the case of ethers) by traces of dehydrogenative silylation products. 

Allyl derivatives of hydrocarbons with functional group were often used as starting materials. The hydrosilylation of allylperfluoroethers with methyl(chloro)silanes is a frequently used method for synthesis (after hydrolysis and polycondensation) of fluorine-containing polymers (162). Unsaturated esters of unsaturated carboxylic acids in the reaction of hydrosilylation give silyl derivatives of carboxylic acid (e.g., 3-methacryloxypropyltriethoxysilane). 

The reaction may be of some preparative interest for obtaining alkylbenzonitriles and various a-functionalized alkylbenzonitriles starting from polynitriles (see Scheme 4.10 and Scheme 4.11) [56,57]. Donors that can be conveniently used as the precursors of the radicals include Jt donors, such as alkenes [58,59] and alkyl aromatics [60-63], heteroatom-centered donors, such as carboxylic acids [64] and ierf-butyl esters [65], ethers [66], ketals [67] (as well as cyclopropanone sUyl ketals) [68] and amines, organometallic donors such as silanes, silyl ethers, and silyl amines [69-71] as well as germanes, stannanes, and borates [72]. 

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