Synthesis of substituted 5-(1,2,4-oxadiazol-5-yl)-3,4-dihydropyrimidine-2(1H)-thiones.

We have developed a liquid-phase route for combinatorial synthesis of novel substituted 5-(1,2,4-oxadiazol-5-yl)-3,4-dihydropyrimidine-2(1H)-thiones. Biginelli-type three-component condensation of 1-(3-aryl-1,2,4-oxadiazol-5-yl)acetones, thiourea, and benzaldehydes is shown to result in new 5-(1,2,4-oxadiazol-5-yl)-3,4-dihydropyrimidine-2(1H)-thione heterocyclic system. If salicylaldehydes are used in this reaction, a mixture of 5-(1,2,4-oxadiazol-5-yl)-3,4-dihydropyrimidine-2(1H)-thiones and 11-(1,2,4-oxadiazol-5-yl)-2,3,5,6-tetrahydro-4H-2,6-methano-1,3,5-benzoxadiazocine-4-thiones is formed.

A chemical placebo: NaCl as an effective, cheapest, non-acidic and greener catalyst for Biginelli-type 3,4-dihydropyrimidin-2(1H)-ones (-thiones) synthesis.

Despite prior reports of several really effective catalytic and non-catalytic approaches towards Biginelli's 3,4-dihydropyrimidin-2(1H)-ones, an overwhelming number of new catalysts for the Biginelli reaction have been recently published. Most of the catalysts are somewhat exotic, expensive, harmful and even uneffective in the absence of acidic additives. Herein we reduce the "yet-another-one-catalyst" idea to absurdity by proposing NaCl promotes the reaction that actually requires no catalyst, neither rare nor expensive.