Trimethylsilyl iodide catalyst

Me3SiCH2CH=CH2i TsOH, CH3CN, 70-80°, 1-2 h, 90-95% yield. This silylating reagent is stable to moisture. Allylsilanes can be used to protect alcohols, phenols, and carboxylic acids there is no reaction with thiophenol except when CF3S03H is used as a catalyst. The method is also applicable to the formation of r-butyldimethylsilyl derivatives the silyl ether of cyclohexanol was prepared in 95% yield from allyl-/-butyldi-methylsilane. Iodine, bromine, trimethylsilyl bromide, and trimethylsilyl iodide have also been used as catalysts. Nafion-H has been shown to be an effective catalyst. 

Tandem syn addition of alkyl and trimethylsilyl groups can be accomplished with dialkylzinc and trimethylsilyl iodide in the presence of a Pd(0) catalyst.79... 

Both ketals100 and enol ethers101 can be used as electrophiles in place of aldehydes with appropriate catalysts. Trimethylsilyl iodide can be used in catalytic quantities... 

Trimethylsilyl iodide can be substituted for the trimethylsilyl triflate catalyst in the reactions of aliphatic aldehydes. TMSI can be generated conveniently in situ either from trimethylsilyl chloride and sodium iodide in acetonitrile314 or from hexamethyldisilane and iodine in dichloromethane334 or pentane.338 It is noted that neither triisopropylsilane nor PMHS is an effective reducing agent for this purpose when used with TMSI under these conditions.314,334... 

In a related three-component reaction procedure, aryl methyl ketones 724 have been combined with aryl aldehydes 725 and urea 726 at room temperature, using trimethylsilyl iodide as catalyst, to give 4,6-diaryl-3,4-dihydro-2(177)-pyrimidinones 727 <2005HCA2996>. A procedure using zinc iodide and microwave irradiation gave similar products <2007T1981>. 

Trimethylsilyl esters of Bronsted acids such as trimethylsilyl triflate and trimethylsilyl iodide are usefiil as catalysts for trimethylsilyl transfer reactions. An example is given in equation (105). 

Ethers, Esters, and Related Derivatives of Alcohols.—5a-Cholestanyl methyl ether has been cleaved inter alia) and converted into 5a-cholestanol by successive treatment with trimethylsilyl iodide and water.Pyridinium toluene-p-sulphonate has been reported as an efficient and mild catalyst for the conversion of alcohols into their tetrahydropyranyl ethers.Bile acids were efficiently performylated by treatment with 90% HCO2H-HCIO4. Selective base-catalysed... 

Compared with chiral nonracemic a-amino carbonyl compounds - which are not suitable substrates for MBH reaction, mainly due to their racemization under normal conditions after prolonged exposure times to catalyst or due to poor diastereoselectivity " a-keto lactams, enantiopure 3-oxo-azetidin-2-ones 168, readily react with various activated vinyl systems promoted by DABCO to afford the corresponding optically pure MBH adducts 169 without detectable epimerization (Scheme 1.69). " However, the Lewis acid-mediated reaction of electron-deficient alkynes with azetidine-2,3-diones 168 as an entry to p-halo MBH adduets was not very sueeessful the coupling product 170 was achieved with concomitant acetonide cleavage as a single ( )-isomer in low yield, in the presence of trimethylsilyl iodide under BF3 OEt2-induced catalysis (Scheme 1.69). 

The half-lives were reported to be in the range of minutes to hours. Induction periods were observed. Formation of trimethylsilyl iodide was proposed to be the cause of an inductitMi period [399]. The polymerization follows first-order kinetics with respect to the concentrations of the initiator and the catalyst. With respect to concentration of the monomer the reaction is described as being first-order internally. It follows, however, an external reaction order of 1.52 due to the higher polarity of the reaction medium at higher monomer concentrations. The authors tentatively propose that the active species are formed from initiator, catalyst and trimethylsilyl iodide [399] ... 

Scettri et al. reported the aza-Michael addition of aniline to chalcones under solvent-free conditions, promoted by cinchonine. The corresponding products were obtained in good yield but with poor ee (11-58%). The enantioselectivity was improved up to 99% by the addition of an achiral silicon-based Lewis acid catalyst such as trimethylsilyl iodide (TMSI). ... 

Addition of trimethylsilyl cyanide to carbon-carbon triple bonds proceeds effectively in the presence of palladium catalyst to give cyano-substituted alkenylsilanes in good yields. Reaction of trimethylsilyl iodide with alkynes under the coexistence of acetylenic tin compounds gives three-component coupling products effectively. 

The Lewis acid-promoted reaction of acetals with trimethylsilyl (TMS) enolates is valuable for the synthesis of p-alkoxy carbonyl compounds, that is, O-alkylated aldols [44]. This aldol-type reaction is effectively catalyzed by (la) [7d, 43], trimethylsilyl iodide (MesSil) [45] and trimethylsilyl bis(fluorosulfonyl)amide (Me3SiN(S02P)2) [46]. Recently, bis (trifluoromethanesulfonyl) amine (HNTf2) has been found to catalyze the aldol-type reaction. A comparison of HNTf2 with Me3SiNTf2 (lb) in catalytic activity suggests that an initial protodesilylation of TMS enolates with HNTf2 forms (lb) as the actual catalyst [47] (Scheme 9.8). 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

A number of approaches have been tried for modified halo-de-diazoniations using l-aryl-3,3-dialkyltriazenes, which form diazonium ions in an acid-catalyzed hydrolysis (see Sec. 13.4). Treatment of such triazenes with trimethylsilyl halides in acetonitrile at 60 °C resulted in the rapid evolution of nitrogen and in the formation of aryl halides (Ku and Barrio, 1981) without an electron transfer reagent or another catalyst. Yields with silyl bromide and with silyl iodide were 60-95%. The authors explain the reaction as shown in (Scheme 10-30). The formation of the intermediate is indicated by higher yields if electron-withdrawing substituents (X = CN, COCH3) are present. In the opinion of the present author, it is likely that the dissociation of this intermediate is not a concerted reaction, but that the dissociation of the A-aryl bond to form an aryl cation is followed by the addition of the halide. The reaction is therefore mechanistically not related to the homolytic halo-de-diazoniations. 

---