Pyrylium perchlorate, reaction with

In the 1970s, O Leary and Samberg described the reaction of 2,4,6-trimethyl-pyrylium perchlorate 57 with a-chymotrypsin and observed the formation of a protein-pyridinium conjugate [94], Later on, the reaction of the tri-substituted pyrylium salt 58 with the proteins gelatin and a-chymotrypsin [95], glycophorin [96,97] and the Na /glucose cotransporter protein [98] was reported. In all cases, the reaction happened to exclusively involve the proteins lysine residues and formation of the corresponding pyridinium adducts were observed. 

Pyrylium perchlorate, 2,4,6-triphenyl-hydrolysis, 3, 741 nitration, 3, 649 reactions with alkali, 3, 652 with methoxides, 3, 652 with piperidine, 3, 655 synthesis, 3, 869... 

An interesting application of this reaction was the use of macro-molecular anhydrides, namely, styrene-maleic anhydride or vinyl acetate-maleic anhydride copolymers in the presence of perchloric acid as catalyst, these copolymers acylate mesityl oxide or d rpnone to macromolecular pyrylium salts which, with aryl substituents, are fluorescent.No crystalline products could be obtained from succinic anhydride because of the solubility and ease of decarboxylation. 

Glutaconaldehyde anion serves as an interesting intermediate for the synthesis of heterocyclic compounds. The parent pyrylium perchlorate has been prepared from glutaconaldehyde and 70% perchloric acid in ether at -55°.° The reaction of glutaconaldehyde anion with alkyl and aryl isothiocyanates and... 

Nitropyrido[l,2-A]quinolin-6-ium-l 1-olate (6%) was isolated from a reaction mixture obtained by photoirradiation of crystalline photochromic 2-(2, 4 -dinitrobenzyl)pyridine for 10 days <2004JP0865>. Reaction of l-(3-chloropropyl)-6,7-dimethoxy-3-methylbenzo[c]pyrylium perchlorate with hydrazines and hydroxylamine in refluxing MeOH afforded 9,10-dimethoxy-6-methyl-, -4,6-dimethyl-l,2,3,4-tetrahydropyridazino[6,l-tf]isoquinoli-nium, and 9,10-dimethoxy-6-methyl-l,2,3,4-tetrahydro[l,2]oxazino[3,2- ]isoquinolinium, perchlorates, respectively <2004CHE1131>. 

Trimethylpyrylium perchlorate is a very versatile and useful starting material. Thus its reaction with cyclopentadienyl-sodium has made 4,6,8-trimethylazulene 12 easily available for general studies of the properties of azulenes 18 and for the synthesis of related compounds.14 In addition, pyrylium salts are readily converted to a variety of pyridine derivatives 9 15 as well as to derivatives of nitrobenzene16 and phenol.9 17,18 It is clear that its value as a starting material is such that it is receiving wide use. 

Unsubstituted 4//-pyran (5) as well as its 4-methyl derivative react with trityl perchlorate or with PC15 to give pyrylium salts of the 157a type.7,90 The reaction of 5 with hydrogen sulfide in the presence of hydrogen chloride gave... 

The series of equilibria allow a change in the anion of a pyrylium salt to be accomplished. The readily available pyrylium perchlorates and tetrafluoroborates are converted into the pseudobases on treatment with weak bases. Reaction of these diketones with a wide variety of acids leads to the new pyrylium salt generally in high yield (Table 9) (80T679). In some... 

The formation of a mixture of pyrylium salts when 2-acetylpyridine and chalcone reacted in perchloric acid was overcome by treating the reactants with ethanolic sodium hydroxide. The pentanedione was isolated and subsequently oxidized by reaction with chalcone and boron trifluoride (82JCS(P1)125). 

Another approach starting with the cyclopenta[c]pyrylium perchlorate 38, followed by condensation with hydrazine, should have given a hydrogenated precursor of 34. However, the reaction gave an oil in a very low yield and it could not be completely characterized. Only the peak of m/z = 286 in a mass spectrum of the raw product confirmed the existence of the 2,6,7,8-tetrahydro-l,4-diphenylcyclopenta[r7]-l,2-diazepin 39 (Equation 3). 

Reactions of pentafluorophenyl-substituted pyrylium perchlorates with hydrazine hydrate are known to give 1,2-diazepines. 2-Pentafluorophenyl-4,6-diphenylpyrylium perchlorate reacts with hydrazine hydrate like the unfluorinated analogue, forming 3,5-diphenyl-7-pentafluorophenyMH-l,2-diazepine. However, the 2,6-di(pentafluorophenyl)-... 

The reaction of 1,3-disubstituted benzothieno[2,3-c]pyrylium salts 81 with hydrazine has been studied. It has been shown that these pyrylium salts interact with hydrazine to give Ar-amino-l, 3-dialkylbenzothieno[2,3-c]pyiidines 82. In contrast, l,3-diphenylbenzothieno[2,3-c]pyrylium perchlorate gives exclusively 5//-[2,3]benzothieno[2,3-/ ]diazc-pine 83 <1998CHE983> (Scheme 16). 

Synthesis of heterocycles. The 1,5-diketone (1) on reaction with trityl perchlorate undergoes dehydrogenative cyclization to the pyrylium salt (2), which is transformed by reaction with ammonium acetate into the pyridine derivative (3). ... 

A detailed study of this dehydrogenative condensation in the presence of triphenylmethyl perchlorate or fluoroborate was made by Simalty-Siemiatycki and Fugnitto. The reaction is best carried out in refluxing acetic acid nitromethane or acetonitrile give less satisfactory results. Chalcone reacts in these conditions with phenylacet-aldehyde yielding 2,4-diphenylpyrylium with an unsubstituted a-position. This and similar 2-unsubstituted pyrylium salts prepared by this method are so reactive that they do not afford pyridines on treatment with ammonia in the usual conditions this behavior is similar to that of the unsubstituted pyrylium perchlorate. The reaction of... 

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