Pyrylium perchlorate

Pyrylium perchlorate, 4-chloromethyl-2,6-dimethyl-ring opening recyclization and, 3, 660... 

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... 

On the other hand, 1,1,1-trisubstituted alkanes behave similarly to aldehydes, yielding pyrjdium salts (128) with identical substituents in positions 2 and 6. Thus, Dorofeenko and co-workers condensed 2 moles of acetophenone with 1 mole of benzotrichloride in the presence of perchloric acid obtaining 2,4,6-triphenjdpjTylium perchlorate with 1 mole of ethyl orthoformate, they obtained 2,6-diphenyl-pyrylium perchlorate (57) from o-hydroxyacetophenone, ortho-formic ester and perchloric acid, 4-ethoxybenzopyrylium perchlorate was formed. 

A suspension of an aryl-substituted pyrylium perchlorate (1.5 mmol) in MeCN (10 mL) was treated with NaN, (0.39 g, 6 mmol) with agitation. The mixture was evaporated and the residue was extracted with Et20. The extract was centrifuged and then evaporated under reduced pressure. This procedure was carried out three times to give the product. 

Phenyldibenz[r/,/][l,3]oxazepine (3) is obtained in 25% yield by treatment of the dibenzo-pyrylium perchlorate 1 with sodium azide, followed by heating the resulting azide 2 (vide supra).2 5... 

Hydrazine hydrate (0.16 mL, 3.2 mmol) was added to a stirred suspension of a pyrylium perchlorate (1.55 mmol) in EtOH (14mL). After 30 min at 20 C the product was collected. 

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>. 

The rate of perchloric acid introduction should be slow at first so that in the range of 40-50° crystals of the 2,4,6-trimethyl-pyrylium perchlorate will begin to appear. Then the rate of addition should be increased to maintain the temperature in the optimum range of 100-105°. If the temperature rises too rapidly, no crystals will appear and the yield will be somewhat lower. Then seeding is helpful. 

Q Which of the following heterocycles conform to the Huckel rule (4h +2) for aromaticity (i) furan (ii) l//-azepine (iii) pyrylium perchlorate [chlorate(VIl)] ... 

Suggest a mechanism for the conversion of pyridinium-fV-sulfonate into pyrylium perchlorate [chlorate(Vll)] in two steps, the hrst being the action of aqueous sodium hydroxide, and the second treatment with perchloric acid in diethyl ether and methanol. 

Similarly, 2,3,4,6-tetramethyl-2//-pyran is accessible from the corresponding pyrylium perchlorate.212... 

The strongly electrophilic pyrylium perchlorate 160a was readily reduced with cyclooctatriene,213 toluene, anisole, dimethylaniline,214 or diphenyl-methanol215 to 2,6-bis(methoxycarbonyl)-4//-pyran (161a). Other perchlorates like 160 exhibit similar behavior toward alcohols equilibrium constants for the redox processes were estimated.216... 

Triphenylphosphine adds smoothly to 2,6-diphenylpyrylium iodide, perchlorate, or tetrafluoroborate to provide 4 -pyranyltriphenylphosphonium salts 215a (80 to 99%).24,262,262a The analogous addition of phosphoranes XC6H4COCHPPh3 to the pyrylium perchlorate or hydrogen sulfate led to salts 216.251... 

The steps of the process have been discussed in detail.354 Bis-2,6-methoxycarbonyl-4//-pyrans 161a,b were converted to the corresponding pyrylium perchlorates 160a,b by perchloric acid as the oxidizing agent.215... 

Pyrylium saltsUnlike the usually used pyrylium perchlorate salts, pyrylium sulfoaeetates are not explosive. They are readily prepared as shown for the preparation of 2,4,6-trimcthylpyrylium sulfoacetatc (2). 

There is evidence that the 2H-pyrans are thermodynamically more stable than their 4//-isomers. For example, the addition of methoxide ion to 2,6-diphenyl- and 4-methoxy-2,6-diphenyl-pyrylium perchlorates (46 R = H and R = OMe) was followed by NMR spectroscopy. The formation of the 4H-pyran (47 R = H or OMe) is rapid and at — 30 °C... 

The formation of furans from pyrylium salts under oxidative conditions has been mentioned in Section 2.23.2.2. Ring opening and recyclization of 4-chloromethyl-2,6-dimethyI-pyrylium perchlorate (83) by aqueous alkali and DMF leads to 2-methylfuran-4-ylacetone (84) (77CHE918). When 2,3,4,5-tetraphenylpyrylium perbromide is hydrolyzed to the dienone and then subjected to bromination-dehydrobromination, 2-benzoyl-3,4,5-triphenylfuran (85) is formed. 

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... 

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