Similarity silyl triflate

The Pummerer reaction of 3,3-dibenzoyloxyethyl-thietane 1-oxide 32a with thymine in the presence of trimethyl-silyl triflate (TMSOTf), triethylamine, and Znl2 in dichloromethane allowed the synthesis of the thietane-derived thymidine 33a in 70% yield <1996TL7569>. The treatment of thietane-1-oxide derivative 32b under similar conditions but in toluene resulted in the modified nucleoside 33b in 30% yield (Scheme 9) <1996TL7569>. 

Mukaiyama aldol reactions using a catalytic amount of a Lewis acidic metal salt afford silylated aldols (silyl ethers) as major products, but not free aldols (alcohols). Three mechanistic pathways which account for the formation of the silylated aldols are illustrated in Scheme 10.14. In a metal-catalyzed process the Lewis acidic metal catalyst is regenerated on silylation of the metal aldolate by intramolecular or intermolecular silicon transfer (paths a and b, respectively). If aldolate silylation is slow, a silicon-catalyzed process (path c) might effectively compete with the metal-catalyzed process. Carreira and Bosnich have concluded that some metal triflates serve as precursors of silyl triflates, which promote the aldol reaction as the actual catalysts, as shown in path c [46, 47]. Three similar pathways are possible in the triarylcarbenium ion-catalyzed reaction. According to Denmark et al. triarylcarbenium ions are the actual catalysts (path b) [48], whereas Bosnich has insisted that hydrolysis of the salts by a trace amount of water generates the silicon-based Lewis acids working as the actual catalysts (path c) [47]. Otera et al. have reported that 10-methylacridinium perchlorate is an efficient catalyst of the aldol reaction of ketene triethylsilyl acetals [49]. In this reaction, the perchlorate reacts smoothly with the acetals to produce the actual catalyst, triethylsilyl perchlorate. 

Silylation of Alcohols. Primary, secondary, and tertiary alcohols are silylated by reaction with TBDMS triflate in excellent yields. For instance, treatment of r-butanol with 1.5 equiv of TBDMS triflate and 2 equiv of 2,6-lutidine in CH2CI2 at 25 °C for 10 min gives a 90% yield of (r-butoxy)-r-butyldimethylsilane. The following alcohols are similarly silylated in excellent yields (70-90%) 2-phenyl-2-propanol, ewufo-norbomeol, c/s-2,2,4,4-tetramethylcyclobutane-l,3-diol, and 9-O-methylmaytansinol (converted to the 3-TBDMS derivative) (eq I). ... 

Hoffmann and coworkers further extended the scope of this reaction to chiral acetals to achieve asymmetric [4-1-3] cycloadditions [30]. Under similar Lewis acid catalysis, the homoacetal derivatives of 105 prepared from 2 equiv of chiral alcohols proceeded to cycloadditions, but this approach suffered from the difficulty of cleaving the chiral auxiliary from the cycloadduct, as well as being wasteful of 1 equiv of the chiral alcohol, which was eliminated. Hoffmann and coworkers then devised the use of mixed chiral acetals such as 117 as chiral oxyallyl cation precursors (Scheme 18.25). They demonstrated that under silyl triflate... 

Another analogue of HTI which was used with either ketones or silyl enol ethers was [hydroxy(mesyloxy)iodo]benzene, PhI(OH)OS02Me [25]. A related reagent formed in situ from iodosylbenzene and trimethylsilyl triflate, probably PhI(OSiMe3)OTf, reacted similarly with silyl enol ethers to afford a-ketotriflates (see Table 5.3). /1-Diketones and /1-ketoesters underwent tosyloxylation by HTI the reaction was very effective in substrates with a perfluoroalkyl moiety and gave their hydrates [26] ... 

Friedel-Crafts alkylation has been used in an important synthesis of aryl C-glycosides, which are potent anti-tumor agents, from glycosyl fluorides (equation 99)65 661. The reaction takes place rapidly in dichloromethane, at room temperature using a novel zirconium complex and silver perchlorate combination catalyst. A similar alkylation has been performed by replacing the aromatic compound with either a silyl enol ether or an allylic compound using silver triflate as the catalyst662,663. 

Mukaiyama and co-workers developed a chiral Lewis acid complex 15 consisting of tin (II) triflate and a chiral diamine. An aldol reaction of enol silyl ether 16 and octanal is promoted by 15 to give 17 in a highly diastereo-and enantioselective manner. The enantioface of the aldehyde is selectively activated by coordination with 15. This method is similar to method 3, in that an aldehyde-chiral Lewis acid complex can be regarded as a chiral electrophile. An advantage of method 4 over method 3 is the possible catalytic use of a chiral Lewis acid. In the reaction of Scheme 3.6, 20 mol% of 15 effects the aldol reaction in 76% yield with excellent selectivity.9... 

The reaction of enol trimethylsilyl ethers of carbonyl compounds with (a,a-dihydroperfluoroalkyl) phenyliodonium triflates required promotion by potassium fluoride to proceed at room temperature to give the P-perfluoroalkyl carbonyl compounds in good yields.225 in the case of the silyl enol ether of an a,p-unsaturated ketone (119), the 6-perfluoroalkyl-o,p-unsaturated carbonyl compound (120) was the only product formed. The reaction is likely to follow a path similar to the one used in the reaction of silyl enol ethers with (perfluoroalkyl)phenyliodonium salts. In a first step, a ic-complex is formed which evolves into the cationic product of a- or y-addition, followed by desilylation to the carbonyl reaction product. 

If the electrophile is a vinyl triflate, it is essential to add LiCl to the reaction so that the chloride may displace triflate from the palladium o-complex. Transmetallation takes place with chloride on palladium but not with triflate. This famous example illustrates the similar regioselectivity of enol triflate formation from ketones to that of silyl enol ether formation discussed in chapter 3. Kinetic conditions give the less 198 and thermodynamic conditions the more highly substituted 195 triflate. 

Trimethylsilylation has been accomplished with a large number of reagents most of which are commercially available. The cheapest (chlorotrimethylsilane) and the most reactive (trimethylsilyl triflate) rapidly silylate hydroxyl groups in the presence of a suitable base such as pyridine, triethylamine, i-Pr2NEt, imidazole, or DBU but an aqueous workup is required to ensure complete removal of the resultant amine hydrochloride or triflate whence hydrolysis of the nascent TMS ether may occur. In some cases the insoluble salt may be removed by filtration without aqueous workup. A wide range of solvents can be used for the reaction such as dichloromethane, acetonitrile, THF, or DMF. Care must be taken with trimethylsilyl triflate (TMSOTf) since it will convert aldehydes and ketones to the corresponding enol silanes and it will open epoxides in a reaction that has preparative significance [Scheme 4.6]. Similar transformations can be accomplished with tert-butyldimelhylsilyl triflate (TBSOTf) or triethylsilyl triflate (TESOTf). ... 

Treatment of 294/295 with HCl gave diols 296/297 in 95% yield. These diols were protected either by reaction with benzyl bromide to give benzyl ethers 298/299 (63%) or by reaction with terf-butyldimeth-ylsilyl triflate to give silyl ethers 300/301 (62%). The latter silyl ethers were separable by semipreparative HPLC and were shown to equilibrate at 75 °C in toluene. In a similar way ligands 302 and 303 were used to prepare complexes 304/305 and 306/307, as mixtures of diastereomers, respectively (Scheme 58). 

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