Trifluoromethanesulfonic acid -promoted

The perchloric acid catalyzed acylation of selenophene with acetic anhydride is claimed to give solely 2-acetylselenophene <81MI 2l3-0l>. Ethoxalyl chloride reacts at the same position <83BEP896054>. Reaction with trifiuoromethylsulfenyl chloride and stannic chloride gives 2-trifluoromethylthioselenophene, and addition of trifluoromethanesulfonic acid promotes formation of the 2,5-bis(trifluoromethylthio) derivative <83JFC(23)525>. 

Several groups explored the use of [2 + 2 + 2] cycloadditions to form highly functionalized quinazolines. Hua andYang developed a new one-pot synthesis of benzo [/]quinazolines 71, involving a trifluoromethanesulfonic-acid-promoted [2 + 2 + 2] cycloaddition of l,4-diaryl-l,3-butadiynes with nitriles and a subsequent intramolecular hydroarylation (Scheme 33) (13CL769).While the yields were low to moderate, the facility of the reaction and availability of starting materials were noted as some of the advantages of this method. 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

Opening by trimethylsilyl trifluoromethanesulfonate yields an adduct (54) from which trifluoromethanesulfonic acid can be eliminated to give an allylic alcohol (Scheme 47) (79JA2738) [cf. base-promoted isomerization to allylic alcohols (Section 5.05.3.2.2)]. 

Ldnn, H, Sulfurylchloride trifluoromethanesulfonic acid — a novel promoter system for glycoside synthesis using thioglycosides as glycosyl donors, Glycoconjugate J., 4, 117-118, 1987. 

Kawano and Togo introduced an ionic liquid group into iodoarenes, to form ionic liquid-supported iodoarenes, and used them for the promotion of the synthesis of oxazoles [24]. The results of the reactions of acetonitrile, m-chloroperbenzoic acid (mCPBA), trifluoromethanesulfonic acid (TfOH), and acetophenone are shown in Table 12.1, using various IL-supported iodoarenes (IL-supported Phis). The reactivities of IL-supported iodoarenes (Phis) 17-25 are shown in entries 1-9, and IL-supported Phi 20 showed the best reactivity. Instead of acetonitrile as solvent, room temperature ILs, such as [emim][OTs], [bmim][PFg], and [bmpyjlNTf ], were used in the presence of IL-supported Phi 20 (entries 10-12). However, [emim][OTs] did not promote the oxazole formation at all, while [bmimJPF and [bmpy][NTfJ provided the oxazole in moderate to low yields. Thus, use of acetonitrile as solvent yielded the best reactivity as compared with these ILs. 

Initially, the method was based on the differential reactivity conferred on each of the partners by the nature of the protecting groups and by the intrinsic nucleophilicity of the thioaryl leaving groups. However, as the method evolved, it became clear that the choice of the promoter was also an important factor to take into consideration. Indeed, it was demonstrated that a disarmed thioglycoside could be activated in the presence of powerful thiophilic promoters such as A-iodosuccinim-ide/trifluoromethanesulfonic acid (NIS/TfOH), whereas it remained inactivated in the presence of weak thiophilic reagent such as iodonium dicollidine perchlorate or methyl triflate [43,45]. 

Strong acids promote electrophilic hydroxylation of aromatics. Thus, sodium perborate - trifluoromethanesulfonic acid has been found to be a versatile reagent for the monohydroxylation of arenes to phenols [55b]. 

Benzyl 2.2,2-trichloroacetimidate (bp 106-114 00.07 kPa) alkylates alcohols in the presence of trifluoromethanesulfonic acid. Esters, imides, isopropylidene and benzylidene acetals are unaffected. This method allows the formation of benzyl ethers in molecules that are base-sensitive. In the example [Scheme 4.167],2 benzylation of the p-hydroxy ester 167.L1 under the usual basic conditions would lead to retro-aldol reactions and/or elimination. A synthesis of the cellular messenger L-a-phosphatidyl-D-/nyo-inositol 3,4-bisphosphate exemplifies the use of trityl cation-promoted benzylation of two adjacent hydroxyls [Scheme 4.168]. ... 

Gramstad, T. and Haszeldine, R.N., Perfluoroalkyl derivatives of sulfur. VII. Alkyl trifluoromethane-suRonates as alkylating agents, trifluoromethanesulfonic anhydride as a promoter for esterification, and some reactions of trifluoromethanesulfonic acid, J. Chem. Soc., 4069,1957. 

The acid-promoted intramolecular Schmidt reaction of azido-alkene 114 is featured in the formal synthesis of gephyrotoxin. Treatment of 114 with trifluoromethanesulfonic acid followed by L-Selectride reduction of the resultant iminium ions 115 and 116 generates a mixture of diastereomeric bromo-amines. The bromide is replaced with acetate ion, and the acetate is reduced to give alcohol 117, a known intermediate in the synthesis of gephyrotoxin. 

Prof. Hao s synthesis commenced with the copper(I) chloride-catalyzed oxidation of the tryptamine derivative to afford ketone 42 [74], A three-component Strecker-type reaction was designed to react the ketone 42 with tryptamine and TMSCN to finish the first ring closure. After examining a series of both Lewis acid and Bronsted acids, the authors found a catalytic amount of TMSOTf promoted the transformation and afforded nitrile intermediate 43, which is ready for the Houben-Hoesch-type cyclization [75]. Treatment by TfOH (trifluoromethanesulfonic acid) [76] in DCM and the... 

---