Perchlorates trityl

Although trityl perchlorate is used to accomplish the glycosidation of the C-8 hydroxyl in 44 with acetoxy glycoside 49, control experiments have demonstrated that no reaction takes place in the presence of 4 A molecular sieves or 2,6-di-terf-butylpyridine. This observation suggests that the actual catalyst is not trityl perchlorate, but perchloric acid. Consistent with this conclusion is the observation that catalytic amounts of a strong Brpnsted acid such as triflic or perchloric acid can catalyze the glycosidation of 44 with 49 in the absence of trityl perchlorate. 

All attempts to effect direct dehydrogenation of tetrahydro- and octahydroindeno[1,2-t/]aze-pines with palladium on charcoal or with trityl perchlorate have failed.57... 

Benzaldehyde can be condensed with the N-silylated urethane 671 and aUyltri-methylsilane 82 in the presence of trityl perchlorate to give, via an intermediate 0,N-acetal, the substituted urethane 672 in high yield [197]. 0,N-Acetals such as 673 condense with the enol silyl ether of acetophenone 653 in the presence of TMSOTf 20 to give the co-hydroxyurethane 674 in 94% yield [198] (Scheme 5.62). 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

Bis(4-formylphenyl) succinate 2201 and octamethylene N,N -bis(trimethylsilyl) carbamate 2202 condense with aUyltrimethylsilane 82 in the presence of 10 mol% trityl perchlorate or TMSOTf 20 to give, after 24 h at 0°C in CH2CI2, the poly-... 

Superior yields of ethers from aldehydes are obtained by the use of several other electrophilic species. The addition of 5 mol% of trityl perchlorate to a mixture of triethylsilane and 3-phenylpropanal in dichloromethane at 0° produces an 83% yield of bis-(3-phenylpropyl) ether within 10 minutes (Eq. 176),329 Reductive polycondensation of isophthalaldehyde occurs with two equivalents of triethylsilane in the presence of 10 mol% of trityl perchlorate to give 40-72% yields of polyether with average molecular weights ranging from 6,500 to 11,400 daltons (Eq. 177).337 Addition of one equivalent of an alkoxytrimethylsilane to the reaction mixture produces unsymmetrical ethers in good to excellent yields. Thus, a mixture of (ii)-cinnamaldehyde, 3-phenylpropoxytrimethylsilane, and triethylsilane in dichloromethane reacts under the influence of a catalytic amount of trityl perchlorate to give the unsymmetrical ether in 88% yield (Eq. 178).329... 

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... 

During the past decades, the scope of Lewis acid catalysts was expanded with several organic salts. The adjustment of optimal counter anion is of significant importance, while it predetermines the nature and intensity of catalytic Lewis acid activation of the reactive species. Discovered over 100 years ago and diversely spectroscopically and computationally investigated [131-133], carbocations stiU remain seldom represented in organocatalysis, contrary to analogous of silyl salts for example. The first reported application of a carbenium salt introduced the trityl perchlorate 51 (Scheme 49) as a catalyst in the Mukaiyama aldol-type reactions and Michael transformations (Scheme 50) [134-142]. 

The reactions proceeded efficiently under mild conditions in short time. The silyl enol ethers reacted with the activated acetals or aldehydes at -78 °C to give predominant erythro- or threo-products [136, 137] respectively. In the same manner, the aldol reaction of thioacetals, catalyzed by an equimolar amount of catalyst, resulted in <-ketosulfides [139] with high diastereoselectivity. In the course of this investigation, the interaction of silyl enol ethers with a,]3-unsaturated ketones, promoted by the trityl perchlorate, was shown to proceed regioselec-tively through 1,2- [141] or 1,4-addition [138]. The application of the trityl salt as a Lewis acid catalyst was spread to the synthesis of ]3-aminoesters [142] from the ketene silyl acetals and imines resulting in high stereoselective outcome. 

Recently it was found that the aldol reaction of silyl enol ethers with acetals or aldehydes is effectively promoted by a catalytic amount of trityl perchlorate to give the corresponding aldols in good yields (44,45). Polymer-bound trityl perchlorate also successfully catalyzed the aldol reaction (45). 

The trityl perchlorate mediated reaction of 1-0-acylsugars with alcohols is successfully carried out at 0 °C and the corresponding 0,-glycosides are stereoselectively produced (47). 

Similarly, C-glycosylation reaction of I-0-acylsugars with silylated carbon nucleophiles, such as silyl enol ethers, proceeded to give the corresponding C-glycosides in good yields in the presence of a catalytic amount of trityl perchlorate ( ). This reaction was also catalyzed by ploymer-bound trityl perchlorate (Mukaiyama, T. Kobayashi, S. Carbohydrate Research, in press.)... 

From azobis(2-pyridyl)- and diazoalkanes a series of 3,3-disubstituted [1,2,4]triazolo[4,3-a]pyridines (77) have been prepared.122 If one of the substituents at position 3 is a hydrogen atom, the triazolopyridinium salt can be obtained by treatment with trityl perchlorate.122... 

Unsubstituted 4//-pyran (5) as well as its 4-methyl derivative react with trityl perchlorate or with PC15 to give pyrylium salts of the 157a type.7,90 The reaction of 5 with hydrogen sulfide in the presence of hydrogen chloride gave... 

The same approach allows preparation of various pyrylium carboranes from the corresponding 4/f-pyran carboranes 174a,b and 175b by the action of acetyl perchlorate,245 perchloric acid,244 and triarylamine radical cation salts,244,245 as well as electrochemically.243 The oxidation of condensed 4H-pyran 345 with trityl perchlorate, 2,3,5,6-tetra-substituted 4f/-pyrans 431 and 153 with tropylium tetrafluoroborate or 153 with heterocyclic salt 393 led to useful preparations of pyrylium salts 394,330 395a,359 and 395b,360 respectively. 

Bis-4,4 -pyrylium salts 214 (R = r-Bu, Ph) were obtained from trityl perchlorate with 163b,c221 or perchloric acid with spirocyclic 4//-pyran 18.52... 

The agents used for oxidative aromatization of 2/f-thiopyrans were trityl perchlorate,42-155,156 tetrafluoroborate,267 and iodide.267 Thus 3,5-diphen-yl-2//-thiopyran (222) was found to aromatize either on its own to thiopyrylium salts 396 or by S-methylation to l-methyl-3,5-diphenylthiabenzene (398) via intermediate 397,267 as shown in Scheme 18. 

Other aromatizations of 2//-thiopyrans with trityl perchlorate were accomplished in the following transformations 399a - 400a, 55 399b - 400b,156 14 - 401,42 and 286 - 402.42 The similar reaction 399c - 400c155 is not an oxidation process. 

Selenopyran (8) was converted to selenopyrylium perchlorate 256 or chloride with trityl perchlorate or phosphorus pentachloride, respectively.90... 

Both the radical ion (40) and the alkali metal salts (41) react unusually with trityl perchlorate, giving 2,2, 5,5 -tetraphenyl-l,l -diarsolyl (44) as a deep red crystalline solid (m.p. 209-212 °C). This reforms the lithium or potassium salt (41) on reaction with the metal in an inert solvent (74TL303). These reactions are shown in Scheme 9. 

The 1-benzothiopyrylium salts are best prepared from the easily accessible thiochroman-4-one [Eq. (35)].6,51,52,302-304 The common dehydrating agents include potassium hydrogen sulfate8 and phosphorus pentoxide51,302-304while sulfuryl chloride/perchloric acid51,302-304 and trityl perchlorate 6 have been useful as hydride extractors. Another method involves the cyclization of /1-ketosulfides (e.g., 81) or j8-arylthio-acroleins (82) with perchloric acid [Eq. (36)].305,306... 

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