Ethyl (4-benzyloxyphenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate and a redetermination of ethyl (4RS)-4-(4-methoxyphenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate, as its 0.105-hydrate, both at 200 K: subtly different hydrogen-bonded ribbons.

Abstract

Two sulfanylidene-1,2,3,4-tetrahydropyrimidine derivatives have been synthesized using acid-catalysed cyclocondensation reactions between thiourea, ethyl 3-oxobutanoate and substituted benzaldehydes. In each of ethyl (4RS)-4-(4-benzyloxyphenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate, C21H22N2O3S, (I), where Z' = 2, and ethyl (4RS)-4-(4-methoxyphenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate 0.105-hydrate, C15H18N2O3S·0.105H2O, (II), the reduced pyrimidine ring adopts a conformation intermediate between the boat, screw-boat and twist-boat forms. In (I) and (II), a combination of N-H...O and N-H...S hydrogen bonds links the organic molecules into ribbons containing alternating R2(2)(8) and R4(4)(20) rings. In (I), the ribbon contains three types of ring, viz. two different R2(2)(8) rings which are both centrosymmetric and R4(4)(20) rings which are not centrosymmetric. In (II), the ribbon contains two types of ring, both of which are centrosymmetric. In compound (II), the ribbons enclose continuous channels which run along the twofold rotation axes in the space group C2/c, and the partial-occupancy water molecules lie within these channels. Structural comparisons are made with a number of related compounds.