Polyphosphoric acid trimethylsilyl ester PPSE

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)... 

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). 

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>. 

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 Pummerer rearrangement can also be invoked by the use of polyphosphoric acid trimethylsilyl ester (PPSE). Using this method, Kakimoto and Imai reported the synthesis of the unusual product phenyl phenylthioglyoxylate 33. The reaction was thought to proceed via phosphorylation of the sulfoxide oxygen rather than silylation as rearrangement did not take place when tris(trimethylsilyl)phosphonate was... 

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],... 

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... 

PPSE = polyphosphoric acid trimethylsilyl ester Scheme 5.221... 

PPSE trimethylsilyl polyphosphate (polyphosphoric acid trimethylsilyl ester)... 

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). 

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