Trimethylsilylated compound

Silylnitronates 1 are prepared14-24,25 by metalation of primary nitroalkanes with lithium diisopropylamide and treatment of the lithionitronates with either chlorotrimethylsilane or (/er/-butyldimethyl)chlorosilane. Nonaqueous workup and distillation gives the silylnitronates in >75% yield as moisture sensitive, but thermally stable, products. (e/7-Butyldimethylsilylni-tronates are more stable than the corresponding trimethylsilyl compounds. 

Nitronium fluoborate also reacts with silylallenes, as indicated in Eq. 13.40(38], Attack of the electrophile at the allene carbon atom distal to the silicon atom, 1,2-silicon migration and ring closure lead to a silyloxazole. Exposure of this material to bromine in a second step gives 124 in 72% overall yield from 123. This annula-tion is best performed with tert-butyldimethylsilylallenes. With trimethylsilyl compounds, protodesilylation is a competing side reaction. 

TBA-F.3H20 (20 mg, 0.063 mmol) is added to the carbonyl compound (10 mmol) and the trimethylsilyl compound (12 mmol) in THF (25 ml) at 0°C. The mixture is allowed to come to room temperature and is stirred until the reaction is complete (ca. 1 h), as shown by GLC analysis. Aqueous HC1 (1 M, 5 ml) is added and the mixture is stirred until all of the silane has been hydrolysed (1-15 h). The aqueous mixture is extracted with Et20... 

PhCHO (1 mmol), the trimethylsilyl compound (2 mmol), and TBA-Ph3SiF2 (54 mg,... 

Since trimethylsilylarenes can be prepared by metallation of the arene followed by treatment with chlorotrimethylsilane, this provides an alternative route into a range of difficult substitution patterns. For example, the ortho/para directing effects of the methoxy groups in 1,3-dimethoxybenzene 75 direct the electrophile to the 4-position. However, lithiation of 1,3-dimethoxybenzene takes place at the 2-position. Reaction with chlorotrimethylsilane then gives the 2-trimethylsilyl compound 76, which undergoes ipso substitution with the electrophile to give the 1,2,3-trisubstituted product 77 (equation 39)101,102. 

The utility of the DePuy fluoride-induced desilylation reaction 38 for the regioselective generation of gas-phase carbanions from trimethylsilyl compounds (equation 13) has... 

A second method for the preparation of neutral pentacoordinate complexes consists of an exchange reaction between chloromethylchlorosilanes (ClCH2SiMe Cl3 , n = 0-2) and N-trimethylsilylated compounds, as shown for example in equation 2989. The compounds of types 96-99 were prepared by this method89-93. The same reagent was used extensively for the synthesis of O Si complexes, and this is discussed in more detail in the corresponding section (III.B.l). 

Such ionic species could also be detected in solution by 29Si NMR spectroscopy. Nucleophiles like TV-methylimidazole, pA M-dimethylaminopyridine and HMPA showed the strongest coordinating effects110. Mixtures of electrophilic trimethylsilyl compounds and nucleophiles(L), such as amines and amides, are common silylation agents111 and salts Me3SiL+X have been discussed as the active silylation species112. 

Magnesium reacts with naphthalene and higher polycyclic aromatics in liquid aimnonia or HMPA to form the radical ion. Adducts with anthracene and substituted anthracenes form in THF. Depending upon substitution and conditions, they have a variety of structures. The l,10-bis(trimethylsilyl) compound had structure (47) in the crystal, with magnesium bridging the 1,10-positions (C-Mg =... 

Modified Peterson reaction. This reagent was used in an unusual application of the Peterson reaction. The a-trirtiethylsilyloxy aldehyde (1) was converted in 80% yield to the Ws-trimethylsilyl compound (2) by treatment at - 35" with 0.95 equiv. of trimethylsilyllithium in HMPT. Nucleophilic attack at the carbonyl carbon was followed by silicon migration to the secondary alkoxide. The reaction of 2 with 3 equiv. of lithium diisopropylamide in THE containing 5% HMPT at 23" gave the saturated aldehyde 3 in 80% yield. The reaction was used to convert a hindered >C=0 into >CHCH20H. 

Trimethylsilyl compounds with electron-withdrawing substituents (CN, I, Cl, Br, N, NCO, CNO, etc.) have been used in syntheses based on the hard-soft reactivity principle, with the silicon atom having electropositive and the substituent electronegative character. The bond between the pseudo-halide trifluoromclhyl and the trimethylsilyl center should also polarize with the trifluoromclhyl group bearing substantial negative charge.23-24... 

The substituent effects observed for tris(trimethylsiloxy)silanes (Me3Si 0)3Si X (75) are the opposite of those observed for the pentamethyldisilanyl and trimethylsilyl compounds. In this case electronegative substituents (such as -CCI3) at Si are found to have a shielding effect relative to X = CH3. As is the case for the pentamethyldisilanes, the substituent effects are opposite for Si and Si . Although both and give linear correlations with Taft cr constants, the slopes have different signs. (75)... 

Since 0-trimethylsilyl compounds are very similar to the corresponding 0-alkyl compounds, the polar, hydrophilic uridine (150) is persilylated with hexamethyidisilazane (HMDS) with evolution of ammonia to the tetrasilylated-activated lipophilic intermediate 151, the structure of which... 

Dimethylarsinomethylenetrimethylphosphorane is available by desilylation of the corresponding 1 -trimethylsilyl compound (c/. Section 1.6.1.3.2)... 

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