4- pyrimidines thermolysis

Flash vacuum thermolysis (FVT) of 2-substituted 4//-pyrido[l,2-n]pyrimidin-4-ones 126 above 800 °C afforded (2-pyridyl)iminopropadie-none (130) (99JCS(P2)1087). These reactions were interpreted in terms of reversible ring opening of 4//-pyrido[l,2-n]pyrimidin-4-ones to imidoyl-ketenes 127. A 1,5-H shift in 127 generated the N(l)H-tautomeric methylene ketene 128, in which facile elimination of HX took place via a six-membered cyclic transition state 129 to yield 130. In the case of 2-methoxy derivative 126 (X = OMe) another competing pathway was also identified at lower temperature, which resulted in the formation C3O2 and 2-methylaminopyr-idine via mesoionic isomer 131 (Scheme 9). The products were identified by IR spectroscopy. 

Flash vacuum thermolysis of 2-dialkylamino-4//-pyrido[l, 2-u]pyrimidin-4-ones 126 (X = NMe2, NEt2) at 850 °C led to the formation of 4H-pyrido[],2-u]pyrimidin-4-one (Scheme 13). The product was identified by NMR and GC-MS (99JCS(P2)1087). 

Heating diethyl (2-pyridylamino)methylenemalonates 304 (R = COOEt, = Me, OH) in AcOH afforded 4-oxo-4//-pyrido[l, 2-n]pyrimidine-3-carboxylates 305 (R = Me, OH) (96JHC1041). Flash vacuum thermolysis of 2-substituted 3-(2-pyridylamino)acrylates 304 (R = CN, COOEt, R = H) through a packed silica tube (530 °C, 0.01 mmHg) gave 3-substituted 4//-pyrido[l,2-n]pyrimidm-4-ones 306 (R = CN, COOEt) (94AJC1263). Ethyl 7-methyl-4-oxo-l, 4-dihydro-1,8-naphthyridine-3-carboxylate (79%) was... 

An early example of N/C replacement leading to a pyrimidine-pyridine conversion is observed on thermolysis (240 °C) of 2,4,6-triphenyl-4-methyl-3,4-dihydropyrimidine. During the thermolysis ammonia evolves and in... 

A kinetic study of thermolysis reactions of TV-crotyl substituted 1,2,4-triazoles was performed at temperatures in the range of 260-350 CC <00JHC1135>. Thermolysis of tetrazolo[l, 5- >]pyridazines, tetrazolo[l,5-a]pyrimidines and tetrazolo[l,5-a]pyridines allowed easy ring contraction to a facile preparation of cyanopyrazole heterocycles . 

Wentrup and co-workers have carried out systematic flash vacuum thermolysis studies with a series of fused tetrazoles. Investigations of the isomeric tetrazolo[l,5- ]pyrazine 17 and tetrazolo[l,5-f]pyrimidine 20 showed that, in both cases, ring contraction takes place to afford imidazoles in high yields, but isotope labeling experiments revealed that the mechanisms of the openings of the two ring systems are different <2002JOC8538>. 

As noted in the Introduction sulfenic acids are generally unstable and reactive. A few, namely, anthraquinone-1-sulfenic acid [1], anthraquinone-l,4-di-sulfenic acid [2], and the sulfenic acid [3] (generated by thermolysis of sulfoxide [4]) have, however, been isolated as pure crystalline compounds (Bruice and Sayigh, 1959 Bruice and Markiw, 1957 Chou et al., 1974). Another sulfenic acid that appears to be of considerable stability is the pyrimidine derivative [5]. The silver salt of [5] was isolated by Pal et al. (1969) from the alkaline hydrolysis of the corresponding disulfide. The free sulfenic acid [5] was then liberated in solution by treating the silver salt with dilute aqueous hydrochloric acid and filtering off the silver chloride formed. Solutions... 

Tetra-r-butylpyridazine (34) is converted into its Dewar isomer (35) when irradiated in pentane with UV light of wavelength > 300 nm. Irradiation of this product at shorter wavelengths, or thermolysis, gives rise to further reaction (91TL57). Irradiation of 4-amino-2,6-dimethylpyrimidine gives the acyclic amino imine via the Dewar pyrimidine as shown in Scheme 2a. The photoisomerization of perfluoropyridazines to pyrazines is considered also to involve Dewar diazine intermediates. 

Reaction of 5,7-dimethyl-l,2,4-triazolo[l,5-a]pyrimidine (246) with phenacyl bromide gave the triazolopyrimidinium salt 247 (85JCS(P1)2333 85TL1321). Treating 247 with one equivalent of triethylamine gave the ylide 248, whose thermolysis in acetonitrile gave Af-cyano-lV-phenacylaminopy-rimidine (249), but when 247 was treated with two equivalents of triethylamine, the 2-iminooxazoline 250 was formed, which was also obtained from 249 by further treatment with another equivalent of triethylamine (Scheme 46). 

Thermolysis of the formamidrazone 590, obtained from the reaction of hydrazine 488 with Vilsmeier salt 589, at 200°C or on boiling in nitrobenzene led, by intramolecular transformation, to the triazolo[4,3-c]pyrimidine 591 (90T3897). Aryl isocyanide dichlorides reacted with 488 in the presence of Et2N to give 3-anilinotriazolopyrimidines (592) (Scheme 117). 

Tetrazolof l,5-c]pyrimidine, 8-amino-7-chloro-purine synthesis from, 5, 591 Tetrazolopyrimidines purine synthesis from, 5, 591 Tetrazolof 1,5-a]pyrimidines cycloaddition reactions, 5, 881 reactions, 5, 880 ring opening, 5, 880 structure, 5, 859, 860 synthesis, 5, 902 thermolysis, 5, 881 Tetrazolof 1,5-c]pyrimidines hydrogenation, 5, 881 reactions, 5, 881 structure, 5, 859, 860 synthesis, 5, 902 thermolysis, 5, 881... 

Thermolysis of [150] produces chemiluminescence due to emission from [151] and [152]. In the case of [151] the emission is due to an exciplex (Becker et al., 1981). Pyrimidines linked by a polymethylene chain and dihydropyri-dines similarly linked undergo intramolecular cycloaddition (Koroniak and Golankiewicz, 1978 Potts et al., 1977). 

Sammes and his group (77JCS(P1)663 78JCS(P1)1293 81JCS(P1)1909) attempted the thermal intramolecular cycloaddition of the substituted pyrimidine 507 possessing an alkyne to produce a monoterpene alkaloid ( )-actinidine (511)(Scheme 64). Upon thermolysis of the pyrimidine 507 at 200°C in a sealed tube, using dimethylformamide as solvent, intramolecular cycloaddition led to the known pyridone 509 in 87% yield by the loss of the amide bridge from intermediate 508. Conversion of the pyridone 509 into the chloropyridine followed by reductive dechlorination afforded racemic actinidine 511. 

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