PPSE

Folyphosphoric acid trimethylsilyl ester (PPSE)[1] can be used in sulfolane, CH,Cl2 or nitromethane. It is similar to polyphosphoric acid but the overall conditions arc milder and the work-up more convenient. PPSE has been used in the cydization of ris-arylhydrazones of cyclohexane-l,2-diones to give indolo[2,3-a]carbazole analogues[2],... 

The polymerizations of polyethersulfone (PES) and polyphenylsulfone (PPSE) are analogous to that of PSE, except that in the case of these two polymers, solvents which are higher boiling than DMSO are needed due to the higher reaction temperatures required. Diphenyl sulfone, sulfolane, and... 

NMP are examples of suitable solvents for PES and PPSF polymerizations. Chlorobenzene or toluene are used as cosolvents at low concentrations. These cosolvents form an azeotrope with water as they distill out of the reaction mixture, thereby keeping the polymerization medium dehydrated. Potassium carbonate is a suitable choice for base. The synthesis of PES and PPSE differ from the PSE case in that the reaction is carried out in a single-step process. In other words, the formation of the dipotassium salt of the bisphenol is not completed in a separate first step. Equations 2 and 3 represent polymerizations based on the dipotassium salts of bisphenol S and biphenol to make PES and PPSE, respectively. 

An interesting synthesis of quinolizidines was achieved using a vinylogous variation of the Bischler-Napieralski reaction. Angelastro and coworkers reported that treatment of amide 26 with PPSE (polyphosphoric acid trimethylsilyl ester) followed by reductive... 

Recently, the protected dimethoxy derivative 152 has been isolated in 70% yield from the Boc-protection of a nonseparable product mixture of the corresponding 2,8-dimethoxyindolo[3,2-h]carbazole 153 and the isomeric indolo[2,3-c]carbazole derivative (cf. Section VI) obtained by a double Fischer cycUzation using PPSE (00MI2). 

Benzoic acids 194 react at 160 °C with 2 equivalents of anilines 192 in the presence of polyphosphoric acid trimethylsilyl ester (PPSE) 195 (which is prepared by reaction of P2O5 with HMDSO 7) to give the amidines 196 in 69-88% yield [30, 31] (Scheme 4.10)... 

On thermolysis of bis(trimethylsilyl) malonate 337 at 160°C in the presence of P4O10 carbon suboxide 339 is formed in 54% yield, via 338 two equivalents of tri-mefhylsilanol 4 are also formed and react in situ with P4O10 to give polyphosphoric acid trimethylsilylester (PPSE) 195 [118] (Scheme 4.44). Pyrolysis of trimethylsilyl 2,2-dimefhylmalonate at 700°C gives dimethyl ketene and HMDSO 7 [118a]. 

When heated in ethylene chloride at 80 °C for 3h the y9-ketosulfide 1203 reacts with the trimethylsilyl ester of polyphosphoric acid (PPSE) 195 (prepared from P2O5 and HMDSO 7) to give 36% 1204 and 8% 1205, whereas the lactone 1206 affords with PPSE 195 the unsaturated sulfide 1207 in 93% yield [27] (Scheme 8.10). 

The N-silylated enol acetate 1523 is cyclized by TMSOTf 20 in CHCI3, in 95% yield, giving the oxazole 1524 [57]. The dimeric derivative 1525 affords the 2,2 -bis-oxazole 1526 in 46% yield [57]. 2-Benzoylamino-3-chloropyridine 1527 is cyclized by polyphosphoric acid trimethylsilyl ester (PPSE) 195 on heating for 15 h in boiling 1,2-dichlorobenzene to give 40-60% 2-phenyloxazolo[5,4-f)]pyridine 1528 [58] (Scheme 9.34). 

PPSE = polyphosphoric acid trimethylsilyl ester Scheme 5.221... 

Conversion of 3,6-dihydro-277-l,2-thiazine 1-oxides 91 to 677-1,2-thiazines 92 takes place in the presence of the dehydrating agent polyphosphoric acid trimethylsilyl ester (PPSE) (Equation 5) <2001TL4183>. 

Trimethylsilyl polyphosphate (PPSE),1 The reagent is prepared from P205 and [(CHj),Si]20. It is a colorless, volatile liquid, soluble in the usual organic solvents. It is comparable to polyphosphate ester for the Beckmann rearrangement of oximes to amides (3, 230 231). but it is prepared more easily. 

Beckmann rearrangement. PPSE is comparable to PPE for Beckmann rciiiTungcmcnt of oximes to amides (equation II). 

Activation of the Beckmann rearrangement of the enantiopure spirocyclic keto oximes (—)-(12) and (—)-(13) has been initiated with four acidic promoters.17 In two cases (PPE and PPSE), concerted [1,2]-shift of the anti carbon operates exclusively. This is not the case with PPA or Eaton s reagent, although optical activity is fully maintained in these ring expansions. 

Treatment of the isomeric dihydroselenines 93 containing electron-withdrawing groups in both the 2- and 6-positions with w-chloroperbenzoic acid also leads to formation of Pummerer-type oxidation products, the 4H-selenines 94 and the corresponding w-chlorobenzoate ester by-products (Equation 39) <1999J(P1)1155>. The esters could be converted to the corresponding 477-selenines by treatment with polyphosphoric acid trimethylsilyl ester (PPSE), a useful reagent for eliminations under neutral conditions. These 4/7-selenines were key intermediates in the synthesis of selenabenzenes. 

The last step in the synthesis of the sulfur- and selenium-containing psoralen analogues (174) (7/7-thieno[3,2- ][l]benzothiopyran-7-one, 7//-seleno[3,2-/][l]benzothiophen-7-one, 2//-selenolo [3,2- ][l]benzothiopyran-2-one, and 7//-selenolo[3,2-g][ 1 ]benzoselenopyran-7-one) was the poly-phosphoric acid silyl ether (PPSE)-mediated cyclization of benzol-thiophenes or selenophenes shown in Equation (76) <92H(34)lli9>. 

Alkyl iodides. Many primary, secondary, and benzylic alcohols are converted into alkyl iodides by reaction with sodium iodide in the presence of PPSE. The reaction proceeds with inversion in the case of secondary alcohols. Yields of 80-98% are often obtainable, but isomerization or elimination can be important side reactions, particularly in the cases of allylic alcohols, 1,2-diols, and tertiary alcohols. 

Early applications of Se02 as a dehydrogenation reagent were limited to compounds like 1,2-diarylethanes and 1,4-diketones which afforded conjugated unsaturated products [28]. Recently, the first aromatization of cyclohexenes 67 and cyclohexadienes 68 by selenium dioxide activated with trimethylsilylpolyphos-phate (PPSE) has been reported [29]. It was found that the reaction described by Eq. (12) resulted in the formation of a variety of aromatics 69 in yields between 80 and 100 % when substrates were refluxed in carbon tetrachloride for 16 - 22 h. 

Trimethylsilyl iodide converts alcohols to iodides. The disadvantage of this method is the expensive reagent, which is avoided if trimethylsilyl chloride and sodium iodide are used instead (equation 27). Trimethylsilyl polyphosphate (PPSE), which is prepared from hexamethyldisiloxane and phosphorus pentoxide, also activates alcoholic hydroxy groups for substitutions with iodide anions (equation 28). ... 

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