Multicomponent reactions (MCRs) and microwave-assisted organic synthesis (MAOS) have been used as key methods for the synthesis of fused dihydropyrimidine derivatives. The three-component condensation of 3-amino-5-alkylthio-1,2,4-triazoles with aromatic aldehydes and acetoacetamides under microwave irradiation was developed as a rapid and efficient solution-phase method for the high-yielding preparation of 7-aryl-2-alkylthio-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxamide libraries. In addition, the selective reduction of the formed dihydrotriazolopyrimidines to trans-trans-2-alkylthio-7-aryl-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxamides was established. The described synthetic protocols provide rapid access to novel and diversely substituted dihydroazolopyrimidine libraries.

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Three-component heterocyclizations of 5-amino-3-methylisoxazole, cyclohexanedione derivatives, and aromatic aldehydes, including salicylic aldehydes, are studied under conventional thermal heating, microwave irradiation and ultrasonication. A dependence of the direction of the reaction on the structure of the aldehyde and the reaction conditions was found, which allowed selective synthesis of 6,7,8,9-tetrahydroisoxazolo[5,4-b]quinolin-5(4H)-ones and 2,3,4,9-tetrahydro-1H-xanthen-1-ones. Key stages of the reaction mechanisms are discussed.

Multicomponent reactions and organic synthesis with ultrasonic activation have been used as key methods for the synthesis of tetrahydropyrimidine derivatives. The three-component condensation of 1,3-diarylprop-2-en-1-one with ammonia and aldehydes/acetone or N-substituted γ-pyridones under ultrasonic irradiation was developed as a rapid and efficient solution-phase method for the high-yielding preparation of 2-aryl(hetaryl)-4,6-diaryl-1,2,5,6-tetrahydropyrimidines and 2,4-diaryl-1,5,9-triazaspiro[5.5]undec-1-enes. The described synthetic protocol provides rapid access to novel and diversely substituted tetrahydropyrimidines libraries. The simple, primary biological screening showed 98% of inhibitory activity against Mycobacterium tuberculosis for one of tetrahydropyrimidines synthesized.

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The present work is devoted to the investigation of 2,4,6-triaryl-1,2,5,6-tetrahydropyrimidine derivatives. A new facile approach to their synthesis based on the reaction of α,β-unsaturated ketones, carbonyl compounds and ammonia was developed. Some stereochemical features of the compounds obtained were fixed on the base of NMR data (including COSY and NOESY experiments).

Fused pyrimidine derivatives R 0515Microwave-Assisted Three-Component Synthesis of 7-Aryl-2-alkylthio-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxamides and Their Selective Reduction. -A rapid access to the title compounds (15 examples) is accomplished in high yields and excellent purities by the condensation of triazoles with aromatic aldehydes and acetoamides under microwave irradiation in 5 minutes. Selective reduction of the C=C double bond in the pyrimidine ring of products (IV) affords structurally modified tetrahydropyrimidines (V) as single trans-trans isomers. -(CHEBANOV*, V. A.; MURAVYOVA, E. A.; DESENKO, S. M.; MUSATOV, V. I.; KNYAZEVA, I. V.; SHISHKINA, S. V.; SHISHKIN, O. V.; KAPPE, C. O.; J.

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