1.2.4- Triazolo pyrimidines, microwave

A series of l,2,4-triazolo[4,3-u]pyrimidines 52 was synthesized in excellent yield by Dandia and co-workers [98] via a microwave-assisted reaction of the l//-l,2,4-triazol-5-amine, a suitable carbonyl compound and malononitrile in aqueous medium. A variety of aromatic aldehydes and cyclic and aliphatic ketones was successfully used to give the desired compounds 52 in good to excellent yields. The reactions were carried out in a domestic microwave oven (Scheme 38). 

A efficient three-component solution-phase condensation of a 3-amino-5-alkylthio-1,2,4-triazoles with an aromatic aldehyde and an acetoacetamide was developed by Qiebanov and co-workers [100] for the rapid synthesis of 7-ary 1-2-alkylthio, 7-dihydro-1,2,4- triazolo[l,5-a]pyrimidine-6-carboxamides 54. All reactions were completed within 5 min of microwave irradiation at 120°C and provided the desired dihydroazolopyrimidines 54 in high yields and with excellent purities. The cyclocondensation reactions were performed in ethanol and a significant decrease of the product yield was observed when switching the solvent to acetic acid or DMF or when an acidic catalysts was added (Scheme 40). 

An interesting approach for the synthesis of some fused pyrimidines has been reported by Shaaban [102] via reaction of 4,4,4-trifluoro-l-(thien-2-yl)butane-1,3-dione in the presence of triethylorthoformate with 5-aminopyrazole or 1,2,4-aminotriazole or 2-aminobenzimidazole under microwave irradiation. The resulting trifluoromethyl derivatives of pyrazolo[l,5-a]pyrimidine 56, l,2,4-triazolo[l,5-a] pyrimidine 57 and pyrimido[l,2-a]benzimidazoles 58 were obtained in excellent yields and purity (Scheme 42). 

Chebanov VA, Muravyova EA, Desenko SM et al (2006) Microwave-assisted three-component synthesis of 7-aryl-2-alkylthio-4, 7-dihydro-l, 2, 4-triazolo[l, 5-a]pyrimidine-... 

It has recently been found that the ANRORC mechanism is realized in the reaction of 6-bromo-[l, 2, 4]triazolo[4,3-a]pyrimidine 94 with aliphatic amines under microwave irradiation, thus affording Ai-alkyl-[l,2,4]triazolo[l,5-a] pyrimidin-7-amines 95 (Scheme 61) [129]. 

Shaaban showed the possibihty to obtain under the microwave irradiation fused systems, l,2,4-triazolo[l,5-a]pyrimidine 149 and l,2,4-triazolo[3,4-c][l, 2,4]triazine 150, containing a trifluoromethyl group as a substituent in the six-membered ring [131]. 

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