Benzothiopyrylium-4-olates

Schenkel-Rudin and M. Schenkel-Rudin, Hetv. Chim. Acta21, 1456(1944). 

3- aryl derivatives (196 R = Detailed accounts of this work 

4- acetic acids (204). Treatment of these intermediates (204) with 

An alternative route that also gives good yields of 3-arylphthalazinium-l-olates (e.g., 205 Ar = Ph) has been described by Lund and involves thermolysis (100-120 C) of A-arylamino-3-hydroxyphthalimidines (197). This transformation (197 - 196) probably proceeds by formation of a hydrazide (198) prior to cyclodehydration (198 - 1%). Compound 205 (Ar = Ph) is obtained in low yields by lithium aluminum hydride reduction of 4-hydroxy-2-phenyl-l(2//)-phthalazinone 207 (R = OH, = Ph).  

3-Methylphthalazinium-l-olate (196 R = Me, R = H) has been prepared in several ways. Phthalazin-l-one (207 R = R = H) with methyl tosylate gives 208 which at pH 6 liberates the free betaine.The same transformation [207 (R = R = H) - 196 (R = Me, R = H)] is also achieved by treatment of compound 207 (R = R = H) with methyl iodide 

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Pyridinium-3-olates and pyrylium-3-olates react with a variety of monoenes, dienes, and trienes. Each of these systems react readily with dienophiles to yield cycloadducts of type 433. For Z = NMe, an electron-withdrawing X group is required in the dienophile, but with Z = 0 or A-(2-pyridyl) even unactivated alkenes react. 1-Phenylpyridi-nium-3-olate and benzyne give 434 dienes give adducts of type 435. Fulvenes behave as trienes to give adducts across the 2,6-positions 436. 2-Benzothiopyrylium-4-olate 437 gives a thermal dimer across the 1,3-positions. 

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