PPTS pyridinium p-toluenesulfonate

Me2C(OMe)2, DMF, pyridinium p-toluenesulfonate (PPTS). The use of PPTS for acid-catalyzed reactions has been quite successful and is particularly useful when TsOH acid is too strong an acid for the functionality in a given molecule. TBDMS groups are stable under these conditions. 

Pyridinium p-toluenesulfonate (PPTS), dihydropyran, CH2CI2, 20°, 4 h, 94-100% yield. The lower acidity of PPTS makes this a very mild method that has excellent compatibility with most functional groups. 

The wide applicability of the PK reaction is apparent in the synthesis of pyrroles, for example, 45, en route to novel chiral guanidine bases, levuglandin-derived pyrrole 46, lipoxygenase inhibitor precursors such as 47, pyrrole-containing zirconium complexesand iV-aminopyrroles 48 from 1,4-dicarbonyl compounds and hydrazine derivatives. The latter study also utilized Yb(OTf)3 and acetic acid as pyrrole-forming catalysts, in addition to pyridinium p-toluenesulfonate (PPTS). 

A new alcohol and phenol protective group, the l-[(2-trimethylsilyl)ethoxy]ethyl moiety, readily introduced using 2-(trimethylsilyl)ethyl vinyl ether and catalytic pyridinium p-toluenesulfonate (PPTS), has been described76. Cleavage is achieved under near-neutral conditions using TBAF monohydrate (equation 16). 

The ease of hydrolysis can vary enormously in some cases hydrolysis is so easy that inadvertent loss of the protecting group during chromatography becomes a nuisance (such as acetals of a, f3-unsaturated ketones). On the other hand acetals may be so robust that forcing conditions (mineral acid and heat) are required. For example, substrates that contain a basic amino function — even if it is remote — can be quite resistant to hydrolysis, because protonation first takes place at the more basic amino function,18 The resultant positive charge repels the second Q-protonation required to set in motion the hydrolysis. An acid-catalysed hydrolysis of a basic acetal that required refluxing with 6 M HC1 in acetone for 6-10 h19 is illustrated in Scheme 2,3, Perhaps the mildest conditions employ pyridinium p-toluenesulfonate (PPTS, pKa 5.2) in methanol or aqueous acetone exemplified by the transacetalisation reaction taken from a synthesis of the vacuolar H+-ATPase inhibitor Bafilomycin Ai [Scheme 2.4, 20... 

The carbodiimide mediated attachment of dye molecules, such as 5(6)-carboxyfluoresceine or rhodamine B to the model compound penylethylamine proceeds in 78 % and 63 % yields, respectively, using diisopropylcarbodiimide, three equivalents of pyridinium-p-toluenesulfonate (PPTS) and two equivalents of diisopropylethylamine (DIPEA). The above conditions are especially useful when the sodium salts of dyes are used. Examples are eosine Y, erythrosin B and phloxine B because yields of >90 % are obtained when the reactions are conducted in DMF in the presence of HOBt. ... 

Tetrahydropyranyl ethers are stable to bases and the protection is removed by acid-catalyzed hydrolysis. For example, geraniol (1.60) is protected as geraniol tetrahydropyranyl ether (1.80) in the presence of pyridinium p-toluenesulfonate (PPTS) reagent. These ethers are cleaved with PPTS in warm ethanoP (Scheme 1.19). 

Besides the activators mentioned thus far, several additional promoters have been introduced and are summarized in Table 4.6. These include protic and Lewis acids (such as TfOH [290,291]), pyridinium p-toluenesulfonate (PPTS) [292,293], and ZnBr2 [294]. A different type of activation, based on reversible reaction of the promoter with the glycosyl acceptor, was developed by Schmidt [295] and based on this principle, chloral was introduced as a promoter. Activation under essentially neutral conditions can also be achieved using LiC104 [126,158]. 

The dimethyl acetal moiety in 27 is hydrolyzed to the corresponding aldehyde 53 using pyridinium-p-toluenesulfonate (PPTS) in acetone. Then the aldehyde is coupled to sulfone 28 under Julia-Kocienski conditions to provide the desired -alkene 29. 

Other variants on this theme are possible. Thus, if the initially-formed Diels-Alder adduct is directly ketalized as in 2, the derived a-sulfonyl carbanion can be alkylated. Reductive desulfonylation and acidic hydrolysis (with pyridinium p-toluenesulfonate, PPTS) then deliver a 4-substituted... 

The reaction was thoroughly investigated and was found to take place through initial cyclization to trana-isomer, trans- followed by epimerization to the desired c/s-thiolactone 8. The reaction was tested using DCC under various acid-base catalyses. While the use of Boden s catalyst [96] employing 4-JV,iV -dimethylaminopyridine hydrochloride (DMAP HCl) provided 8 in 63% yield, the use of more acidic pyridinium p-toluenesulfonate (PPTS) afforded a much better yield (87%) (Table 10, Entries 2 and 3). Finally, when TFA and pyridine were employed as the additives and a two-step procedure involving initial cyclization to frUFrt5-isomer trans-% at lO C followed by epimerization at 60°C, was conducted, the compound 8 was obtained in 93% yield (Table 10, Entry 4). 

A solution of this ester (8.35 g, 21.6 mmol, 1.0 equivalents) in tetrahydrofuran (THF 100 mL) was cooled to 0 °C, and pyridinium p-toluenesulfonate (PPTS, 500 mg, 2.00 mmol, 0.1 equivalents) and then 2,2-dimethoxypropane (20.0 mL, 163 mmol, 5.9 equivalents) were added. The cold bath was removed and the mixture was stirred at room temperature for 48 h, quenched with saturated aqueous NaHCOs solution, and extracted with EtOAc. The combined organic layers were washed with brine, dried (Na2SO4), filtered, and concentrated. Purification by chromatography on SiO2 (3% ethyl acetate and 1% triethylamine in hexanes, and then 100% EtOAc) afforded the acetonide and a small amount of starting diol which was re-subjected and purified as above. The two batches were combined to afford naphthalene-2-carboxylic acid 2-[(4S)-2,2- dimethyl-[l,3]dioxan-4-yl]-2-methylpropyl ester (9.140 g, 97%) as a clear colorless syrup. Reference Wipf, P Graham, T. H.,/. Am. Chem. Soc. 2004,126, 15346-15347. 

Pyridinium p-toluenesulfonate (PPTS) as a catalyst for protection of alcohols as the tetrahydropyranyl ethers, as well as for cleavage of ethers in warm EtOH (see 1st edition). 

The mildest reagent for cleaving TBS ethers is pyridinium p-toluenesulfonate (PPTS) in a protic solvent — usually methanol. Under these conditions a primary TBS ether can be cleaved in the presence of a 2-(trimethylsilyl)ethoxy-methyl (SEM) ether and 2-(trimethylsilyl)ethyl ester [Scheme 4.26]. Primary TBS ethers cleave at room temperature but secondary TBS ethers may require elevated temperature. In the transformation shown in Scheme 4.27 two TBS ethers were cleaved in the presence of a TIPS ether." rerf-Butyldiphenylsilyl (TBDPS) ethers are impervious to attack under these conditions as evinced by the selective removal of a primary TBS ether in the presence of an equally exposed primary TBDPS ether in a synthesis of NodRm-IV factors, glycolipids produced by symbiotic fungi that elicit formation of nitrogen-fixing root nodules in legumes [Scheme 4.28]. ... 

Compound 6 was treated with n-butyllithium (1 equiv), and the resulting acetylide was added to 5 in tetrahydrofuran to give the adduct (15). Conjugate addition of lithium dimethylcuprate followed by treatment with pyridinium p-toluenesulfonate (PPTS) gave segment A (4) [5b, c]. 

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