Dimroth Rearrangement

Many related examples are now known as the general Dimroth rearrangement. For example, 3-ethylamino-l,2-benzisothiazole (576) is in equilibrium in aqueous solution with the 2-ethyl-3-imino isomer (577) (72AHC(14)43). Dimroth rearrangements are known in the 1,2,4-thiadiazoles (578 — 579) see Section 3.4.3.9.1 (68AHC(9)165). For a similar example in the 1,2,3,4-thiatriazole series see Section 3.4.3.1.9. 

2-Amino-l,3,4-oxadiazoles (580) ring-open and the products immediately recyclize to triazolinones 

Reactivity of Uve-membered Rings with two or More neteroatoms 

Ring-chain equilibria of 1,2,3-triazoles and benzotriazoles with the isomeric a-diazo imines result in the well-known Dimroth rearrangement (see Section 4.01.4.1.1). 

3-triazoles with strong electron-withdrawing group, such as —CN and OSO2CF3 are also known. 

3-Triazolium-l-imides are in equilibrium with l,2-cis-bis(arylazo)ethenes, which have been investigated by variable-temperature NMR 87JCR(S)332 (see Section 4.01.2.5) and by ab initio calculations 90CC882 (see Section 4.01.1.5). 

4 REACTIVITY OF FULLY CONJUGATED RINGS 4.01.4.1 Unimolecular Thermal and Photochemical Reactions 

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Another classical reaction which has been observed is the Dimroth rearrangement, e.g. (46) -> (47) (75JCS(P1)2182), and related reactions lead to the transformations (48) -> (49) (79JHC1169) and (50) ->(51) (76JAP(K)7636485), and to formation of other similar products (69MIP21500). 

The thermal acid- or base-catalyzed interconversion of 5-amino-l-phenyltriazoles (413) and 5-anilinotriazoles (415) was discovered by Dimroth. It is an example of a general class of heterocyclic rearrangements (416 417) now known by the name Dimroth rearrange-... 

Dimroth rearrangement, 5, 438 Imidazolium chloride, 4-chloromethyl-reaction with poly(vinyl alcohol), 1, 306 Imidazolium chloride, 2,4,5-tri(diethylamino)-reduction, 5, 415 Imidazolium complexes, 7, 746... 

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

Dimroth rearrangement, 5, 562 Purine, 2-aIkyI-synthesis, S, 587 Purine, 6-aIkyI-I-oxide... 

Pyrimidin-5-amine, 4-methylamino-synthesis, 3, 121 Pyrimidin-5-amine, 4-oxo-purfne synthesis from, 5, 582 Pyrimidinamines acylation, 3, 85 alkylation, 3, 86 basic pXa, 3, 60-61 diazotization, 3, 85 Dimroth rearrangement, 3, 86 electrophilic reactions, 3, 68 Frankland-Kolbe synthesis, 3, 116 hydrolysis, 3, 84 IR spectra, 3, 64 N NMR, 3, 64 nitration, 3, 69 Principal Synthesis, 3, 129 reactivity, 3, 84-88 structure, 3, 67 synthesis, 3, 129 Pyrimidin-2-amines alkylation, 3, 61, 86 basic pK , 3, 60 diazotization, 3, 85 hydrogenation, 3, 75 hydrolysis, 3, 84 mass spectra, 3, 66 Pyrimidin-4-amines acidity, S, 310 alkylation, 3, 61, 86 basic pXa, 3, 61 Schifi base, 3, 85 synthesis, 3, 110, 114 1,3,5-triazines from, 3, 518 Pyrimidin-5-amines basic pXj, 3, 61 hydrogenation, 3, 75 reactions... 

Triazole, 5-amino-1,4-diphenyl-photo-Dimroth rearrangement, 5, 697... 

Triazolo[4,3-a]pyridine, 3-amino-diazonium reactions, 5, 863 Dimroth rearrangement, 5, 861 Sandmeyer reaction, 5, 862 synthesis, 5, 883... 

Amino-l,2,4-triazole undergoes a cyclocondensation with 3-etlioxyacrolein (7) to form 1,2,4-triazolo[l,5-a]pyrimidine (3) or its [4,3-u] isomer (5), according to whether it reacts as IH or 4H tautomer 2 or 4. Moreover, the pyrimidines 3 and 5 can interconvert by a Dimroth rearrangement. Since the H NMR spectrum 30a does not enable a clear distinction to be made AMX systems for... 

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