Pyridinium toluenesulfonate

Af,Af-Dimethylaminopyridine, triethylamine, CH2CI2, phthalic anhydride Poly(4-vinylphenol), 4-(dimethylamino)-pyridinium 4-toluenesulfonate (0.786 mmol), THF, CH2CI2,4-(trifluorovinyloxy) benzoyl chloride, di-isopropylethyl-amine, 1,2-dicyclohexyl-carbodiimide... 

If the conversion is carried out at 60 °C in triethyl orthoformatc as solvent, the corresponding diethyl acetal is isolated in 100% yield with 60% ee (GC. NMR). The crude reaction mixture obtained is dissolved with acetone, and a few crystals of pyridinium 4-toluenesulfonate are added. The solution is heated to reflux for 5 h. The solvent is removed under reduced pressure and the aldehyde product distilled or flash chromatographed (silica gel, CHC13) (Table 3). 

DMTST (dimethylthio)methylsulfonium PPTS pyridinium 4-toluenesulfonate... 

SCHEME 2 Synthesis of intermediate 13. Tf, trifluoromethanesulfonate PCC, pyridinium chlor-ochromate DMSO, dimethyl sulfoxide PPTS, pyridinium 4-toluenesulfonate EE, ethoxyethyl. 

Pyridinium / -toluenesulfonate, f-BuOH or 2-butanone, reflux, 80-99% yield. This method is useful for allylic alcohols. MEM ethers are also cleaved under these conditions. 

Pyridinium / -toluenesulfonate, 5°, 1 h." Similar selectivity can be achieved using a silica-alumina gel prepared by the solgel method. ... 

A variety of substituted dibenzo-fused derivatives 126 have been prepared for evaluation of their biological activities. The synthesis of these compounds involves the reaction of o-acylanilines with pyrroloindolones 125, in boiling butan-l-ol with pyridinium />-toluenesulfonate as catalyst (Equation 8). Compounds such as 126 which contain the benzo[5,6]pyrrolizino[l,2-A]quinoline skeleton exhibit cytotoxicity against several cancer cell lines <2004BML2363>. 

Pyrroloimidazopyridines can be prepared readily by an interesting reaction between 6-aminomethyl-2-piperidone and the vinyldiketo ester 288. This initially gives compound 289, which can be converted into the pyrroloimidazo-piperidine 290 upon treatment with pyridinium />-toluenesulfonate <1990JOC5821> (Scheme 79). 

Ionic liquids with Bronsted acidity have also been prepared from neutral liquids, such as [BMIM]BF4 and [BMIMJPFg, by dissolving well-known Bronsted acids, -toluenesulfonic acid (TsOH), pyridinium -toluenesulfonate (PPTS), and triphenyl phosphine hydrobromide (TPP.HBr) (101). The strong acidities of the catalysts are maintained in the liquids. 

Tri- and tetrasubstituted oxepanes 47 can be obtained in 50-60% overall yield (Scheme 15) using vinyl radical cyclization of homopropargyl and arylhomopropargyl derivatives 48 of Baylis-Hillman adducts 49, followed by methylidene group deprotection using pyridinium/>-toluenesulfonate (PPTS) <2005TL3369>. 

The last step of the synthesis of the natural product (—)-semburin 329 involved the cyclization of the primary alcohol 328 catalyzed by pyridinium />-toluenesulfonate (Equation 40). In analogous fashion, starting from the suitable primary alcohol, the (—)-isosemburine was also obtained <2002SL334>. Similar acid-catalyzed ring-closure was observed in the synthesis of the benzodioxocin 303 from the dialcohol 330 (Equation 41) <2003JOC1081>. 

Alkylation of amidine 1131 with l-bromo-2-methoxy-2-propene affords regiospecifically N-alkylated product 1132. Treatment of 1132 with pyridinium />-toluenesulfonate in aqueous THF provides imidazole 1133 in good yield. In this reaction, l-bromo-2-methoxy-2-propene is used as a protected form of a-bromoacetone, which itself leads to poor yields when reacted directly with amidines (Scheme 275) <2000J1V1E3168>. 

Catalysis with protic acids has traditionally been used in Fischer glycosylations. As with the recent variations of the above procedure, Lewis acid catalysis is also valuable for dehydrative glycosylations with protected derivatives (Scheme 4.40). Trimethylsilyl triflate has been shown to promote reactions of glucuronic acid hemiacetals [420], and pyridine and TMSOTf was used for the synthesis of cw-glucosides [421]. Pyridinium / -toluenesulfonate (PPTS) was used for the synthesis of glycosides of the biologically important Kdo [422]. 

Thus, chalcone (26), available via aldol condensation between the appropriate benzaldehyde and acetophenone, was transformed into the 1,3-diarylpropene (27) via a two-step sequence involving ethyl chloroformate and NaBH4, followed by protection of the phenolic hydroxy group as the TBDMS ether. Asymmetric dihydroxylation of olefin (2 7) with AD-mix-a gave an intermediate diol, which was converted into ortho-ester (28) with triethyl orthoformate in the presence of catalytic pyridinium -toluenesulfonate (PPTS), followed by deprotection of the TBDMS ether with TBAF in THE. Treatment of ortho-ester (28) with triethyl orthoformate and PPTS gave an intermediate (27( ,35)- w j -flavan-3-ol formate ester. De-esterification with K2CO3 in THF/methanol and oxidation of the... 

A-methylmorpholine A-oxide = pyridinium chlorochromate = 2-phenylsulfonyl-3-phenyloxaziridine = pyridinium p-toluenesulfonate = pyridinium / -toluenesulfonate = pyridine... 

Allylic alcohol 846 has been employed in the synthesis of several natural products, as illustrated in Scheme 114 for the preparation of ( —)-elenolic acid (856), a secoiridoid monoterpene isolated from the olive Olea europea. The initial reaction is an orthoester Claisen rearrangement of 846 using triethyl orthoacetate, followed by lactonization with pyridinium / -toluenesulfonate. The resulting lactone is obtained as a 3 1 mixture of cw-850 and its trans isomer. After stereospecific alkylation of 850 with allyl bromide, the conversion of 851 to 852, which is essentially an expansion of the lactone by insertion of a methylene unit, requires five steps to accomplish. The remainder of the synthesis is uneventful, and furnishes pure 856 [234]. 

An enantioselective synthesis of ( —)-(2i ,3i ,6S,8i )-epi-nonactic acid (124) is shown in Scheme 89. The reduction of (122) with diethylmethoxyborane/sodium borohydride yields a iyn-diol (not isolated), which cyclizes spontaneously to the lactol (123). Pyridinium -toluenesulfonate-catalyzed dehydration, desulfurization with Raney nickel, Rh/Al203-catalyzed hydrogenation, and hydrolysis of the ester group affords (124) <94JOC3898>. 

The pyridinium / -toluenesulfonate (PPTS) generates a mild acidic medium that allows the selective hydrolysis of the oxazoline. This happens by protonation of the nitrogen, followed by an electronic movement that begins in the electron pair in one of the oxygen atoms in the bridge-head acetal, and produces the expulsion of the oxazoline oxygen. 

In a patent by Mitsubishi, it is available via hydroformylation of limonene and subsequent acid-catalyzed intramolecular cyclization of the aldehyde [1]. The alcohol can also be produced in one step by Pt/Sn-catalyzed hydroformylation, suggested by a protocol of Gusevskaya and coworkers (Scheme 5.123) [2, 3]. Platinum and tin are essential for the cychzation in the last step. Alternatively, the tandem reaction has been investigated in detail with rhodium complexes based on PPhg, P[0(o-fBu)Ph]3, or PPTS (pyridinium / -toluenesulfonate)... 

Researchers at Shell discovered that also acids (pyridinium / -toluenesulfonate, H-octanoic acid, phosphonic acids) or metal salts, for example, Ca(OAc)2 or Eu(OAc)j, could improve the rate and selectivity [9]. Moreover, they used bidentate phosphine as ligands, which allowed even the transformation of... 

Scheme 17. Reagents i) pyridinium / toluenesulfonate, CH2CI2, azeotropic dehydration, 73%.

On treatment with a non-enolizable aldehyde and sodium hydride, rruns-related a-hydroxyepoxides were converted to acetals. The reaction is thought to proceed by way of a hemiacetal salt, as illustrated in Scheme 2. L-Galactono-1,4-lactone, a by-product of the sugar industry, furnished a diastereomeric mixture of 5,6-alkylidene acetals 18 in >60% yield on microwave irradiation in the presence of long-chain aldehydes and montmorillonite KSF as catalyst, and 4,6-O-alkylidene derivatives 19 of D-glucose have been prepared by use of long-chain aldehydes and catalytic pyridinium />-toluenesulfonate in benzene under azeotropic removal of water. Compounds 18 and 19 were of interest in liquid crystal studies. 

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