Polyphosphoric acid trimethylsilyl ester

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... 

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). 

Several successful cyclizations of quite complex structures were achieved using polyphosphoric acid trimethylsilyl ester, a viscous material that contains reactive anhydrides of phosphoric acid.58 Presumably the reactive acylating agent is a mixed phosphoric anhydride of the carboxylic acid. 

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>. 

Aminobenzenesulfonamides are ring closed directly to AH- 1,2,4-benzothiadiazine 1,1-dioxides (500) with a variety of carboxylic acids, employing polyphosphoric acid trimethylsilyl ester as the cyclization agent (83S851, 85JAP(K)6025984, 90JMC172l). 

The use of polyphosphoric acid trimethylsilyl ester as a means of condensing aryl, arylalkyl, and arylalkenyl carboxylic acids with o-aminobenzenesulfonamide in a one-pot synthesis gives high yields of... 

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. 

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

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... 

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