Pyrylium, 2,4,6-trimethyl

Azulene, 4,b,8-trimethyl-from pyrylium salts, 3, 660 Azulenes... 

Pyrylium salts, 3-acetyl-2,4,6-trimethyl-crystallography, 3, 625 Pyrylium salts, 3-alkoxymethyl-synthesis, 3, 865 Pyrylium salts, alkyl-deprotonation, 2, 51 reactions, 2, 50 Pyrylium salts, 2-amino-reactions, 2, 55 Pyrylium salts, 4-amino-deprotonation, 2, 55... 

Pyrylium salts, 2,3,4,6-tetramethyl-synthesis, 3, 868 Pyrylium salts, 2,4,6-trialkyl-oxidation, 3, 650 Pyrylium salts, 2,4,6-triaryl-synthesis, 3, 870 Pyrylium salts, 2,4,6-trimethyl-deuteration, 3, 649 synthesis, 3, 861, 868, 873 Pyrylium salts, 2,4,6-trimethyl-4-styryl-reactions... 

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. 

Resonance, similar to that in pyrylium salts, was shown594,595 to exist between oxonium ion (299a) and carbenium ion (299b) forms in alkylated ketones, esters, and lactones that were obtained via alkylation with trimethyl- or triethyloxonium tetra-fluoroborates596 [Eq. (3.78)]. Ramsey and Taft597 used H NMR spectroscopy to investigate the nature of a series of secondary and tertiary carboxonium ions (300-302). 

A solution of 2-vinylbenzofuran 59 (288mg, 2mmol), l,5,5-trimethyl-l,3-cyclohexadiene 60 (488 mg, 4 mmol) and 63a (20 mg, 2mol%) in methylene chloride (120 mL) was cooled to 10-15 °C and irradiated with xenon arc lamp using a filter (2 >345 nm) for 4h. The product was filtered through a short column of silica gel to remove the pyrylium salt and then concentrated. Flash chromatography (cyclohexane) gave 61 (295 mg, 56%). 

The reaction of trimethyl phosphite with sodium iodide in acetonitrile, when tried on 2,6-diphenylthiopyrylium cation (18), failed to give the desired phosphonate 323 (80JOC2453). It has been reported, however, that 2,6-diphenyl-pyrylium (17) and -thiopyrylium (18) bromides react with triethyl phosphite to give the diethyl phosphonates 322 and 323, respectively (7IDOK600). These can be hydrolyzed with HCl to give the pyranyl-and thiopyranyl-phosphonic acids 326 and 327, which treated with triphe-nylmethyl perchlorate give the pyrylium- and thiopyrylium-4-ylphospho-nic acids 328 and 329. 

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