Trimethylsilyl function

With the exocyclic alkylidene at C-13 properly in place, the elaboration of the l,5-diyn-3-ene moiety can now be addressed. Cleavage of both acetate and trimethylsilyl functions in 86 with basic methanol, followed by triethylsilylation of the newly formed tertiary hydroxyl group, efficiently affords alkyne 25 (86 % overall yield). This substance was regarded as a viable candidate for a Pd-catalyzed coupling reaction.12 Indeed, treatment of 25 with (Z)-chloroenyne 26 in the presence of a catalytic amount of Pd(PPh3)4 and Cu1 results in the formation of enediyne 24 in 91 % yield. 

The turnover frequency was found to be greatest for the two fluorous ligands and the control ligand with the trimethylsilyl function was found to be less effective than triphenylphosphine. These fluorous derivatives of Wilkinson s catalyst were used to hydrogenate 1-octene in perfluoromethylcyclohexane (PP2). The reaction was carried out a number of times in order to evaluate the efficiency of the system in terms of recycling and reuse [16], It was found that as the number... 

As previously described, the effect of substituent groups on the silyi function is an important factor in terms of determining the reaction course. Table 4 shows the ratio of the products in the Pummerer reaction using various SKAs.33 These results suggest that carbon-carbon bond formation preferentially occurs when using a small silyi function such as the trimethylsilyl function. This tendency was observed in another substrate which has asymmetric carbon at the (3-position of the sulfur atom (Table 5).33 Interestingly, the syn-selectivity of the rearrangement product... 

The activating influence of the trimethylsilyl function is also apparent in the reduction of naphthalene derivatives (Scheme 40). The 1,4-disilyl derivative (201) is reduced exclusively in the substituted ring to give (202), while 2-trimethylsilylnaphthalene (203) affords a 4 1 mixture of (204) and (205), respectively. " As would be expected, the reduction of C-silylbenzoic acids and their esters is controlled by the carboxy function."... 

The photochemical cycloaddition of ethene to the bis-butenolides (20) has been examined in an attempt to establish the influence of the ether-protecting groups of the diol system. Generally only two adducts are formed as can be seen from the results shown for the appropriate structures. The most effective ether protecting group is the trimethylsilyl function and here the facial selectivity yields predominantly the anti,anti adduct (21). With the unprotected systems (20, R = H), there is virtually no selectivity and in this case the three adducts (21), (22) and (23) are formed. Irradiation of the butenolides (20a) and (20b) in the absence of ethene leads to intramolecular hydrogen abstraction (a Norrish Type II process) with the formation of the products (24a) and (24b) in 79% and 76%, respectively. 

Dialkyl ethynylphosphonates are the simplest but not the easiest of these compounds to prepare. Several approaches had been described, but no convenient high-yield synthesis appeared until the introduction of the trimethylsilyl functionality as a protecting group for the acetylenic C-H linkage. 

Instead of the commercially available CpZrHCl, this reagent can be prepared in situ from Cp2ZrCl2 and lithium triethylborohydride. The reaction mixture hydrozirconates terminal acetylenes without affecting e.g. an ester or trimethylsilyl functionality in the alkyne. An application of the Schwartz reagent in natural product synthesis is the hydrozirconation of the terminal triple bond of Me3SiC=C(CH2)4C=CH. A review on hydrozirconation has been published . ... 

A feature of many aliphatic TMS-efher pectra is the low intensity of the molecular ion. However, most have an ion at M -15, due principally to a loss of a methyl group from the trimethylsilyl function, which helps to establish the identity of the molecular ion. It occurs at an odd mass value in the absence of an odd number of nitrogen atoms. In contrast, TMS-ether-methyl esters of hydroxy aromatic acids have a significant ion. 

Cumulenic anions, C=C=C and C=C=C=C, without strongly electron-withdrawing substituents are much stronger bases than acetylides, "CsC- and are therefore also stronger nucleophiles. In view of the poor stability of the cumulenic anions at normal temperatures this is a fortunate circumstance the usual functionalization reactions such as alkylation, trimethylsilylation and carboxylation in most cases proceed at a sufficient rate at low temperatures, provided that the... 

The chlorosilanes are clear Hquids that should be treated as strong acids. They react readily with water to form corrosive HCl gas and Hquid. Liquid chlorosilanes and their vapors are corrosive to the skin and extremely irritating to the mucous membranes of the eyes, nose, and throat. The nitrogen-functional silanes react with water to form ammonia, amines, or amides. Because ammonia and amines are moderately corrosive to the skin and very irritating to the eyes, nose, and throat, silylamines should be handled like organic amines. Trimethylsilyl trifluoromethanesulfonate and trimethylsilyl iodide form very corrosive acidic products. 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

N,N - Bis(trimethylsilyl)sulfur(rV) diimide Me3SiN=S=NSiMc3 is an especially versatile source of the N=S=N functionality in the formation of both acyclic and cyclic S-N compounds. It is conveniently prepared by the reaction of NaN(SiMc3)2 and thionyl chloride (Eq. 2.5). 

A large number of silylating agents exist for the introduction of the trimethylsilyl group onto a variety of alcohols. In general, the sterically least hindered alcohols are the most readily silylated, but are also the most labile to hydrolysis with either acid or base. Trimethylsilylation is used extensively for the derivatization of most functional groups to increase their volatility for gas chromatography and mass spectrometry. 

In the initial report by Corey and Chaykovsky, dimethylsulfonium methylide (2) reacted smoothly with benzalaniline to provide an entry to 1,2-diphenylaziridine 67. Franzen and Driesen reported the same reaction with 81% yield for 67. In another example, benzylidene-phenylamine reacted with 2 to produce l-(p-methoxyphenyl)-2-phenylaziridine in 71% yield. The same reaction was also carried out using phase-transfer catalysis conditions.Thus aziridine 68 could be generated consistently in good yield (80-94%). Recently, more complex sulfur ylides have been employed to make more functionalized aziridines, as depicted by the reaction between A -sulfonylimine 69 with diphenylsulfonium 3-(trimethylsilyl)propargylide (70) to afford aziridine 71, along with desilylated aziridine 72. ... 

Acetals are useful because they can act as protecting groups for aldehydes and ketones in the same way that trimethylsilyl ethers act as protecting groups for alcohols (Section 17.8). As we saw previously, it sometimes happens that one functional group interferes with intended chemistry elsewhere... 

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