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5-Bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one was used as an efficient precursor for the synthesis of a new series of (1,2,3-triazol-1-yl)methyl-pyrimidine biheterocycles. For this stepwise synthesis, the 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one was first converted into 5-azido-1,1,1-trifluoro-4-methoxypent-3-en-2-one through a nucleophilic substitution of the bromine by an azide group. This was then followed by an azide–alkyne cycloaddition reaction (click chemistry) to give the key intermediate 5-[4-alkyl(aryl)-1H-1,2,3-triazol-1-yl]-1,1,1-trifluoro-4-methoxypent-3-en-2-ones. These were cyclocondensed with 2-methylisothiourea sulfate to give a series of 2-(methylthio)-4-(1,2,3-triazol-1-yl)methyl-6-(trifluoromethyl)pyrimidines. Additionally, the 2-methylthiopyrimidine products were used to prepare a new series of 2-amino-4-(1,2,3-triazol-1-yl)methyl-6-(trifluoromethyl)pyrimidines.

A study is presented for the synthesis of a series of 1-tert-butyl-3(5)-(trifluoromethyl)-1H-pyrazoles from the reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones [CF3C(O)CH=C(R1)(OR), where R = Et and R1 = H or R = Me and R1 = Me, Ph, 4-Me-C6H4, 4-MeO-C6H4, 4-F-C6H4, 4-Cl-C6H4, 4-Br-C6H4, 4-I-C6H4, fur-2-yl, thien-2-yl, or naphth-2-yl] with tert-butylhydrazine hydrochloride. When [BMIM][BF4] (1-butyl-3-methylimidazolium tetrafluoroborate) and pyridine were used as the reaction media, we obtained a mixture of 1-tert-butyl-3(5)-trifluoromethylpyrazoles. The formation of 5-trifluoromethyl-1-tert-butyl-1H-pyrazoles with high regioselectivity occurred when the reaction was carried out with NaOH in EtOH. The formation of 1-tert-butyl-3-trifluoromethyl-1H-pyrazoles occurred, after hydrolysis of the 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones in H2O and H2SO4, followed by cyclization in [BMIM][BF4] and pyridine.

This paper reports a comparative study of the chemoselectivity and yields of the synthesis of N-alkyl-4-(trihalomethyl)-1H-pyrimidin-2-ones carried out by the cyclocondensation of 4-alkoxy-1,1,1-trihalo-3-alken-2-ones (enones) with methyl- and allylureas with the N-alkylation of 4-(trihalomethyl)-1H-pyrimidin-2-ones with methyl iodide and allyl bromide. To determine the chemoselectivity of the products obtained, all compounds were fully analyzed by 1H and 13C NMR and 2D HMBC spectroscopy. This study has demonstrated that the cyclocondensation reactions give better yields and furnish either N1- or N3-alkylated products depending on both the reaction conditions and the substituents on the enones, whereas the alkylation of pyrimidin-2-ones gives lower overall yields and either an N1-alkylated product or a mixture of N1- and O-alkylated products.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)