Eaton s reagent

However, when an electron-withdrawing group, e.g., a trifluoromethyl group, is attached to the anilines this procedure is not applicable. A way to circumvent this problem was enlightened by Glasnov et al. [53] who treated the malondianilide 14 with Eaton s reagent, a 7.7% solution of phosphorus pen-toxide in methanesulfonic acid (a. Scheme 6) [54]. This reaction is, however, sensitive to time, temperature, and concentration. More reactive malondian-... 

Notes A strong mineral acid of unspecified structure. It contains a mixture of phosphoric acids and derivatives, with a high content of P2O5. Does chemistry similar to that found with Eaton s reagent. 

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. 

Zewge et al. discovered that Eaton s reagent could be used to efficiently promote the cyclization of aniline derivatives to give substituted 4-quinolones <07JOC4276>. As shown below, aniline derivative 105 can be treated with Eaton s reagent at 50 °C for 2 h to provide 4-quinolone 106. 

Likewise, tertiary allylic 1-hydroxycyclopropylcarbinol derivatives (142) and their vinylogous compounds (143) rearrange upon treatment with a catalytic amount of Bp3-Et20 into 2-(hex-l-enyl)-2-methylcyclobutanone (144), a precursor of dihydrojas-mone (145), obtained upon further acidic treatment with the Eaton s reagent (MeS03H-P20s, 10 1) (equation 103). ... 

Conventional condensation of 1,2-diaminobenzene 16 with 6-fluoro-3,4-dihydro-2H-chroman-2-carboxylic acid 17 under Phillips conditions or using Eaton s reagent (1 10 mixture of phosphorus pentoxide/methanesulfonic acid) yielded 2-(6-fluorochroman-2-yl)-lff-benzimidazole 18 (Scheme 4) [30]. However, irradiating the reaction mixture containing polyphosphoric acid as a catalyst with microwaves afforded the compoimd 18 in comparable yields in a matter of three minutes [30]. 

Eaton s reagent (a mixture of phosphorous penfoxide and mefhane-sulfonic acid) is frequenfly ufilized as a very efficienf solvenf cafalysf for fhe preparation of complex polycyclic compounds in fhe "one-pof" domino process involving a cycloacylafion sfep. Thus, diterpenoid systems, quinolones heterocycles 29 (Scheme 2.15), ° flavones and chromones, i and benzo[(j] tellurin-4-ones can be elegantly synthesized by exploiting this reagent. However, the process represents a small-scale production method due to... 

Mulzer then took this a step further, testing the chloro congener (TMP) MgCl and discovering that it was more effective than Eaton s reagent for the... 

Synthesis from Dibasic Acids and Tetraamines in Eaton s Reagent... 

Ueda et al. reported that in some cases, PBIs could be synthesized by polymerization of dicarboxyUc acids and tetraamine hydrochloride salts in Eaton s reagent (a solution mixture of phosphorus pentoxide [P2O5] in methanesulfonic acid [MSA] at the weight ratio of P205/MSA= 1/10, it is also denoted as PPM A) [6]. They also... 

FIGURE 8.6 Synthesis of various PBIs via condensation polymerization in Eaton s reagent. (Reprinted with modification from Ueda, M. et al.. Macromolecules, 18, 2723, 1985. With Permission.)... 

Just like the situation of the polymerization in PPA, here, the tetraamine hydrochloride salts can also be replaced with the free tetraamines and it is preferentially to completely dissolve the free tetraamines in Eaton s reagent prior to the addition of the dicarboxylic acid monomers. However, it should be noted that as the dicarboxylic acids with high electron affinity such as isophthalic acid (iPTA), terephthalic, and 4,4 -dicarboxyldiphenyl sulfone are used as the acidic monomers, the resulting products are only low-molecular-weight polymers [6]. 

In some special cases, Ueda s approach is more useful for PBI synthesis. For example, the authors found that the copolymerization of disodium 4,6-fcis(4-carboxyphenoxy) benzene-l,3-disulfonate (BCPOBDS-Na), 4,4 -dicarboxydiphenyl ether (DCDPE), and 3,3 -diaminobenzidine (DABz) in Eaton s reagent at IdO C yielded organo soluble linear sulfonated polybenzimidazoles (SOPBIs) [7], whereas insoluble gel was obtained when the polymerization was conducted in PPA probably because of the occurrence of cross-linking reactions between sulfonate groups and activated benzene rings. 

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