- The Dimroth rearrangement: Synthesis and interconversion of isomeric triazolothienopyrimidines
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Triazolo-thieno[3,2-e]pyrimidines obtained by cyclisation of 4-hydrazino-2-(methylthio)thieno[2,3-d]pyrimidine with formic acid, acetic acid, cyanogen bromide and carbon disulfide, and by oxidation of the derived aldehyde hydrazones, are found to be the triazolo[4,3-c] isomers. These [4,3-c] compounds resist isomerisation in acid, but they undergo Dimroth rearrangement to the [1,5-c] isomers under basic conditions. The crystal structure of one such rearranged product, 5-methoxy-8,9,10,11-tetrahydro[1]benzothieno[3,2-e][1,2,4] triazolo[1,5-c]pyrimidine (13b) was confirmed by X-ray analysis.
- Hamed, Atef A.,El-Ashry, El-Sayed H.,Zeid, Ibrahim F.,Badr, Hesham F.
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scheme or table
p. 334 - 339
(2009/05/30)
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- Crystal and molecular structure of 2H- and 2-(p-tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones
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The crystal and molecular structure of 2H- and 2-(p-tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones was investigated by X-ray diffraction. In crystals, the tautorneric form with a localized N(1)=C(2) bond is realized. A comparative analysis of the two structures using the literature data is given to examine the conjugation effect on the geometrical parameters of a pseudoaromatic pyrimidine system.
- Tashkhodzhaev,Turgunov,Usmanova,Urakov,Vorontsov,Antipin,Shakhidoyatov
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p. 995 - 1001
(2007/10/03)
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- A facile synthesis of isoxazolo [5′,4′:4,5]thiazolo[3,2-a]thieno pyrimidines a new ring system
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In a one-pot synthesis 6,7-dimethyl-2-arylidine-5-H-thieno[2,3-d]pyrimidine-3,5-diones 2 were prepared via the reaction of a ternary mixture of 5,6-dimethyl-2-thioxo-1,2,3,4-tetrahydrothienol[2,3-d]pyrimidin-4-one (1), chloroacetic acid, and a proper aldehyde. Compound 2 reacted with hydroxylamine to afford 2,3-dihydro-7,8-dimethyl-3-substituted-9H-isoxazolo[5′,4′:4,5] thiazolo [3.2-a] thieno[2,3-d]pyrimidin-9-ones (4). Reaction of 1 with 3-chloropent-2,4-dione in ethanolic potassium hydroxide yielded the S-acetylacetone derivative 5d. The latter compound reacted with hydrazines and thiourea affording the 2-pyrazolthio and the 2-pyrimidinylthio derivatives 11 and 12, respectively. Compound 5d also underwent cyclization on boiling with acetic anhydride/pyridine solution to yield 2-acetyl-3,6,7-trimelhyl-5H-thieno[2,3-d]thiazolo[3,2-a]pyrimidin-5-one (13). The 2-methylthioderivative 5a was converted into the corresponding 2-methyl sulphone derivative 9 on treatment with hydrogen peroxide.
- Abdel-Fattah,Aly,Gad,Zaki,El-Gazzar
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p. 263 - 281
(2007/10/03)
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