Trityl triflate

This mixed anhydride, in combination with a base such as 2,6-di-f-butyl-4-methylpyridine, is a potent reagent for trifluoroacetylation. The reaction of 1 with anthracene results in formation of the 9-trifluoroacetyl derivative (81% yield). Cyclohexanone reacts with 1 to form the enol trilluoroacetate (72% ield). The reaction of trityl chloride and 1 leads to trityl triflate. ... 

Recently Mukaiyama and coworkers introduced the use of trityl salts as efficient catalysts for the aldol reaction. Using a catalytic amount of trityl perchlorate (5 mol %) and t-butyldimethylsilyl enol ethers, the anti aldols were preferentially obtained (anti 73-84%) regardless of the double bond geometry. With trityl triflate (5 mol %) and dimethylphenylsilyl enol ethers, the syn isomers are produced predominantly (syn 63-79% Scheme 1). Several variations of the catalyst system have been developed. Trityl... 

Asymmetric Wittig-Homer reactions Wittig-Horncr reactions have usually involved phosphine oxides, phosphonates, or phosphonamidcs. Highly enantioselcctivc ole-finations have now been achieved by use of this chiral phosphonamidatc 1. Thus the anion (t-BuLi) reacts with 4-/-butylcyclohexane to form 2 in >98% de. Elimination with trityl triflate/2,6-lutidine provides the alkylidene 3 with essentially complete stercospccificity. The reaction was shown to be applicable to a variety of 4-alkylcyclohexanones. 

Because of the high stability of the triphenylmethyl carbocation, the reductive ether cleavage of trityl ethers with EtySiH/trimethylsilyl triflate (TMSOTf) is highly successful. This reaction even occurs in the presence of highly reactive sugar ketals, leaving the ketals intact (Eq. 126).269... 

The use of trimethylsilyl-based electrophilic catalysts with organosilicon hydrides also promotes the conversion of aldehydes into ethers and avoids the need to employ the potentially hazardous trityl perchlorate salt.314,334,338 One reagent pair that is particularly effective in the reductive conversion of aldehydes into symmetrical ethers is a catalytic amount of trimethylsilyl triflate combined with either trimethylsilane, triethylsilane, PMHS,334 or 1,1,3,3-tetramethyldisiloxane (TMDO, 64) as the reducing agent (Eq. 179).314 Either... 

Indeed, a variety of Lewis acids have been shown to effed glycosylation with hemiacetal donors. Ernst and coworkers have used 5mol% of [Rh(III)(MeCN)3 (triphos)] tris(triflate) with 4 A molecular sieves to prepare glycoconjugates 18 and 19 [26]. Mukaiyama s group has used trityl tetrakis(pentafluorophenyl)borate (3-5 mol%) with Drierite in the preparation of disaccharides 20 and 21 [27,28]. In the synthesis of 21, the a-seledivity was shown to arise from in situ anomerization of the (1-pyranoside over time. 

Acid-catalyzed dealkoxylation is particularly suitable for the preparation of highly reactive, cationic iron(IV) carbene complexes, which can be used for the cyclopropanation of alkenes [438] (Figure 3.11). Several reagents can be used to catalyze alkoxide abstraction these include tetrafluoroboric acid [457-459], trifluoroacetic acid [443,460], gaseous hydrogen chloride [452,461], trityl salts [434], or trimethylsilyl triflate [24,104,434,441,442,460], In the case of oxidizing acids (e.g. trityl salts) hydride abstraction can compete efficiently with alkoxide abstraction and lead to the formation of alkoxycarbene complexes [178,462] (see Section 2.1.7). 

The undefined mechanism of the aldol-type Mukaiyama and Sakurai allylation reactions arose the discussion and interest in mechanistic studies [143-145]. The proposed mechanism was proved to proceed through the catalytic activation of the aldehyde and its interaction with the silyl ketene acetal or allylsilane producing the intermediate. From that point the investigation is complicated with two possible pathways that lead either to the release of TMS triflate salt and its electrophihc attack on the trityl group in the intermediate or to the intramolecular transfer of the TMS group to the aldolate position resulting in the evolution of the trityl catalyst and the formation of the product (Scheme 51). On this divergence, series of experimental and spectroscopic studies were conducted. 

Cp has been discussed [170b]. Alkylation with haloalkanes (often iodoalkanes), triflates (alkyl, benzyl, cyclopropyl), or [RsO] (R = Me, Et) is often the best entry to vinylidenes of any particular system. Other common electrophiles, such as halogens (Cl, Br, I), acylium ([RCO] ), azoarenes ([ArN2] ), tropylium ([C7H7] ), triphenylcarbenium (trityl, [CPhs] ), arylthio (ArS) and arylseleno (ArSe) have also been used. 

Homoallyl methyl ethers.4 Trityl perchlorate catalyzes a reaction of allyltri-methylsilanes with dimethyl acetals or ketals to form homoallyl methyl ethers in 60-90% yield. Diphenylboryl triflate is a somewhat less efficient catalyst. Example ... 

Treatment of O-benzoyl anhydrothymidine 64 (R1 =Me R2 = COPh) with MgX2 (X = Br, I) in toluene at 100 °C afforded halo-substituted thymidines 65 (Nu = Br, I) in 70-75% yields <1995NN307, 1995TL873>. Alkylation of O-trityl anhydrothymidine with methyl triflate followed by reaction with NaBr or Nal gave the corresponding N(3)-methylated thymidines 65 (Nu = Br, I) in 70-90% yields <1993TL8411>. 

A convenient method for tritylation of carboxylic acids involves reaction of a trimethylsilyl ester with trityloxytrimethylsilane catalyzed by 1. This reaction is limited to tertiary alkyl trimethylsilyl ethers (equation I). The triflate is an excellent catalyst for thioacetalization with ethylthiotrimethylsilane (equation II). A related... 

N,NyN, KT-tetramethyl-1,2- ediylenediamine 2,2,6,6-Tetramethylpiperidine Trimethylsilyl, tetramediylsilane Trimethylsilyl triflate Tetra-N-propylam monium per r uthenate Triphenyimethyl (trityl)... 

The dissociation constants of trityl and benzhydryl salts are KD 10 4 mol/L in CH2C12 at 20° C, which corresponds to 50% dissociation at 2-10-4 mol/L total concentration of carbocationic species (cf. Table 7) [34]. The dissociation constants are several orders of magnitude higher than those in analogous anionic systems, which are typically KD 10-7 mol/L [12]. As discussed in Section IV.C.l, this may be ascribed to the large size of counterions in cationic systems (e.g., ionic radius of SbCL- = 3.0 A) compared with those in anionic systems (e.g., ionic radius of Li+ 0.68 A), and to the stronger solvation of cations versus anions. However, the dissociation constants estimated by the common ion effect in cationic polymerizations of styrene with perchlorate and triflate anions are similar to those in anionic systems (Kd 10-7 mol/L) [16,17]. This may be because styryl cations are secondary rather than tertiary ions. For example, the dissociation constants of secondary ammonium ions are 100 times smaller than those of quaternary ammonium ions [39]. 

These KD values are much smaller than those of trityl and benz-hydryl salts (lO-MO-4 mol/L) (cf Tables 7 and 16). The KD values of trityl salts correspond to interionic distances of approximately 5 A. The smaller (Kd 107-10-6 mol/L) dissociation constants calculated from the common ion effect in styrene polymerizations with triflate and perchlorate anions correspond to interionic distances =4 A. However, perchlorate and triflate anions may not be spherical, and their dipole moments should therefore also be considered in calculating their interionic distances and dissociation constants. As discussed in Section II.D, specific interactions of counteranions with the ar-H atoms of the secondary carbenium ions may result in lower dissociation constants [39],... 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

Mukaiyama, T., Nagaoka, H., Murakami, M., Ohshima, M. A facile synthesis of homoaiiyi ethers. The reaction of acetals with allyltrimethylsilanes promoted by trityl perchlorate or diphenylboryl triflate. Chem. Lett. 1985, 977-980. 

O-Tritylation.2 A trimethylsilylated alcohol, phenol, or carboxylic acid can be converted into the corresponding trityl derivative by reaction with 1 catalyzed by trimethylsilyl triflate (equation I). t-Butoxytrimethylsilane can be used, but it is less effective. ... 

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