Dimroth rearrangement mechanism

Adenine also may undergo an additional reaction at its C-6 amine group using a Fischer-Dimroth rearrangement mechanism. Alkylation at N-l can result in a rearrangement to give the C-6 alkylated product. The reaction at N-l usually requires... 

In 2014, Odom and coworkers reported a titanium-catalyzed synthesis of 2-amino-3-cyanopyridines (Scheme 3.41) [89]. The reactions were performed in a one-pot manner with two manipulation steps. Firstly, titanium-catalyzed alkyne iminoamination and generation tautomers of 1,3-diimines. Then, 2-amino-3-cyanopyridines were formed in good to modest yields after treatment with base (DBU) and malononitrile. A Dimroth rearrangement mechanism for 2-aminopyridine formation was proposed based on the isolation of a 2-imino-l,2-dihydropyridine intermediate which undergoes rearrangement under the reaction conditions. 

The formation of pyrazoline derivatives 175 (but not dihydrotetrazolotria-zepines 173, as assumed earlier [53]) is brought about by the condensation of chalcones with diaminotetrazole 172 [128,129]. The structure of the compounds 175 is convincingly verified using X-rays. The mechanism of their formation implies a Dimrothe rearrangement for either the initial diamine or for one of the cyclocondensation intermediates (Scheme 4.51). 

The fully-unsaturated 1,3-benzodiazepine 310 is formed by a photoreaction of the 1-substituted isoquinoline 7V-imide 309 (Scheme 169) <1980CPB2602>. The same principle has been applied to prepare thieno-, furo-, and pyrrolo-fused 1,3-diazepines <1980CC454, 1981CPB1539>. The imidazolo-fused l,3-benzodiazepin-2-ones 313 can be prepared by the reaction of 5-amino-4-(cyanoformimidoyl)imidazoles 311 with tosyl isocyanate. The mechanism of this reaction includes a 1-exo-dig cyclization of intermediates 312 followed by a Dimroth rearrangement to give the thermodynamic products 313 (Scheme 170) <1996JHC855, CHEC-III(13.05.9.2.2)174>. 

The Dimroth rearrangement is the most powerful reaction for the synthesis of Af -alkylat-ed adenines starting from N1 alkylated precursors. First observed on 1-methyladenine, which can be obtained from 2 -deoxy-l-methyladenosine by hydrolysis in acidic medium, the scope of this reaction has been greatly extended. The mechanism of this rearrangement has been elucidated, and is shown for the rearrangement of 1-methyladenine to A -methyl-adenine (29). 

Mint Tho, N., Leroy, G., Sana, M., Elguero, J. Reaction mechanism of the Dimroth rearrangement. Ab initio study. J. Heterocycl. Chem. 1982,19, 943-944. 

Perrin, D. D., Pitman, I. H. The Dimroth rearrangement. V. The mechanism of the rearrangement of 1-alkyl-1,2-dihydro-2-iminopyrimidines in aqueous solution. J. Chem. Soc., Abstracts 1965, 7071-7082. 

The best-known example is the Dimroth rearrangement of 1-alkylade-nines to 6-alkylaminopurines, the parameters and mechanism of which have been established and confirmed by the results of recent mass spectral investigations with deuterated 1-alkyladenine derivatives. The effect of various substituent groups on the rate of rearrangement has been examined. In addition to studies with 1-alkyladenines the kinetics of the analogous isomerization with 1-alkoxyadenines have been determined and compared. ... 

Upon UV irradiation, ethyl 5-amino-l-phenyl-l,2,3-triazole-4-carboxylate (40) does not expel N2 to give ketenimines or aziridines. Instead, in the presence of triphenylene as photosensitizer, 40 is smoothly isomerized, as a first example of a photo-Dimroth rearrangement,163 to ethyl 5-anilino-1,2,3-triazole-4-carboxylate (298).164 The mechanism is explained by a radical rearrangement, e.g., 2971-297III (cf. Scheme 81). This isomerization type was observed also with 5-amino-1,4-diphenyl-1,2,3-triazoles.165... 

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