Trimethyl silyl reagents

Organoboranes react with a mixture of aqueous NH3 and NaOCl to produce primary amines. It is likely that the actual reagent is chloramine NH2CI. Chloramine itself,hydroxylamine-O-sulfonic acid in diglyme, and trimethyl-silyl azide " also give the reaction. Since the boranes can be prepared by the hydroboration of alkenes (15-16), this is an indirect method for the addition of NH3 to a double bond with anti-Markovnikov orientation. Secondary amines can be prepared by the treatment of alkyl- or aryldichloroboranes or dialkylchlorobor-anes with alkyl or aryl azides. 

Alternative silylating reagents such as N,0-bis(trimethylsilyl)acetamide 22a (BSA) [39-43], N,0-bis(trimethylsilyl)trifluoracetamide 22b (BSTFA) [44], or N,N-bis(trimethylsilyl)formamide 22c (BSF) [41, 46], in which the N- and O-trimethyl-silyl groups are in equilibrium [45] (Scheme 2.4), are much more powerful silylating reagents [40, 45] but are more expensive than FIMDS 2, because they are usually prepared by heating formamides or acetamides with TCS 14/triethylamine... 

The efficiency of the amination methodology of enolates with 0-phoshinylhydroxyl-amine-type reagents was further demonstrated by Boche and Schrodt in the high-yield amination of 0-(trimethylsilyl)cyanohydrin anions with 4c (Scheme 44)". 0-(Trimethyl-silyl)cyanohydrins prepared by treatment of aryl, hetaryl and conjugated aldehydes with trimethylsilyl cyanide were lithiated to the eniminates. This is a practical method that enables the easy conversion of aldehydes to iV,Ai-dimethylamides under mild conditions. 

Owing to their stability and low nucleophilicity, metal acetylides are less reactive toward Cjq than other lithium organyls or Grignard reagents [11]. Though the reaction is slower and higher reaction temperatures are necessary, various acetylene derivatives of Cjq could be obtained. The first acetylene Cjq hybrids were (trimethyl-silyl)ethynyl- and phenylethynyl-dihydro[60]fullerene, synthesized simultaneously... 

To develop new electrophilic reagents, Ricci and coworkers have described the synthesis of trimethylsilyloxy and hydroxy compounds from magnesium enolates and bis(trimethyl-silyl)peroxide. Magnesium enolates, generated using magnesium diisopropylamide, (DA)2Mg, give the hydroxycarbonyl compounds in excellent yields (equation 72, Table 8). 

When samples of a pure glucose anomer were dissolved in water and a sample removed for silylation within about 30 seconds, only one major peak was obtained, and the chromatogram was indistinguishable from that obtained by treatment of the solid anomer with the standard silylation reagent. Occasionally, minor peaks were present, preceding the peak of the a anomer these may have represented partial trimethyl-silyl derivatives (28). 

Assay Preparation Melt a sample in an oven to obtain a clear and homogeneous liquid. Transfer about 50 mg of melted sample, accurately weighed, into a 10-mL reaction vial with screw cap, and successively add 200 iL of V,0-Bis(trimethyl-silyl)trifluoroacetamide (BSTFA, 99%, silylation reagent) and 800 (xL of pyridine (catalyst). Homogenize by means of a vortex, and silylate for 30 min at room temperature. Dilute with 9 mL of hexane. 

Hydrostannation of (l-alkynyl)carbene chromium complexes involves addition to the M = C bond as well as to the C=C bond and is strongly influenced by the substituent at the alkynyl moiety. By the bulky trimethyl-silyl group of compound lg, a 1,1-addition to the carbene carbon atom is promoted with formation of a densely functionalized 1,3-heterobimetal lie propargyl reagent 93 containing both a stannyl and a silyl group. A 3,1-addition is observed with phenyl derivative la and also the vinyl compound lo, which leads to production of an allene 94 and 95, respectively (Scheme 31).111... 

It is only fair when reviewing syntheses to mention unsuccessful reactions so as to outline any shortcomings of a particular reagent, and this has been done throughout this review. Sah et al. have recently reported that reaction of the metallated lithium phenolate (31) with either nitrobenzene or bis(trimethyl-silyl) peroxide gave only starting material, while reaction with trimethyl borate followed by oxidation furnished a complex mixture. 

A similar dilithium reagent derived from l,l-bis(trimethyl silyl)ethylene has been used for the protecting ligand of the first monomeric stannylene (equation 8) and later, of various kinetically stabilized species (vide infra). Cyclooctatetraene undergoes l,4-(hsilylation as shown below (equation 9). 

Epoxides can react smoothly with allylsilane reagents. For example, 1,3-bis-trimethylsilyl-Tpropene can react with one of a variety of epoxides under Lewis acid catalysis to generate a highly functionalized alkenol (Equation 35). Yields are modest, with best results being obtained using monosubstituted epoxides <1998TL529>. Trimethyl silyl... 

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