Abstract
Certain Biginelli pyrimidines with ester substitution in C5 were subjected to unexpected ring opening upon solvent-free reaction with hydrazine hydrate to give three products: pyrazole, arylidenehydrazines, and urea/thiourea, respectively. The nonisolable carbohydrazide intermediates are formed firstly followed by the intermolecular nucleophilic attack of terminal amino group of hydrazide function on sp2 C6 rather than the sp3 C4 to give the ring adduct which was produced as a final product.
Highlights
Pyrimidine derivatives Uracil and Thymine are an integral part of RNA and DNA, respectively
We identified malonohydrazide as reaction product besides salicylaldehyde azine upon the reaction of ethyl 2-oxo-2H-chromene-3-carboxylate with hydrazine hydrate [43]
In a typical experimental procedure a solution of urea (R = H, X = O, a)/thiourea (R = H, X = S, b), aldehydes a– d (R4 = Ph, 4-MeC6H4, 4-MeO-C6H4, 4-Cl-C6H4), and ethyl acetoacetate (R5 = COOEt, R6 = Me, a) in absolute ethanol was heated under reflux in the presence of catalytic amount of CaCl2 to give the required DHPM derivatives a– h
Summary
Pyrimidine derivatives Uracil and Thymine are an integral part of RNA and DNA, respectively. The reaction of C5 esters with thiosemicarbazide, in acetone, to afford thiosemicarbazones is reported (Figure 1) [39] The latter data stimulate our interest to investigate the reactivity of C5 ester towards hydrazine hydrate under solvent-free conditions which produce three different ring cleavage products. This unexpected result leads us to perform further extensive survey in literature to discover the effect of hydrazine hydrate on pyrimidines other than DHPMs. Interestingly, the reported findings revealed that the hydrazinolysis of pyrimidine-2(1H)-one ( a), 4-methylpyrimidin-2(1H)-one ( b), or 4,6-dimethylpyrimidin-2(1H)one ( c) resulted in the formation of 1H-pyrazole ( a), 3methyl-1H-pyrazole ( b) and 3,5-dimethyl-1H-pyrazole ( c), respectively, in addition to urea ( a) in each case (Figure 2) [40]. In the light of previous data and in continuation of our interest in the chemistry of hydrazine hydrate towards certain heterocycles [44,45,46,47,48], we aim to study the solvent-free reaction of hydrazine hydrate on C5 ester Biginelli pyrimidines a– h (Figure 3)
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