Buthalital and methitural – 5,5-substituted derivatives of 2-thio­barbituric acid forming the same type of hydrogen-bonded chain

The mol­ecule of buthalital, (I) [systematic name: 5-(2-methyl­prop­yl)-5-(prop-2-en-1-yl)-2-sulfanyl­idene-1,3-diazinane-4,6-dione], C(11)H(16)N(2)O(2)S, exhibits a planar pyrimidine ring, whereas the pyrimidine ring of methitural, (II) [systematic name: 5-(1-methyl­but­yl)-5-[2-(methyl­sulfan­yl)eth­yl]-2-sulfanyl­idene-1,3-diazinane-4,6-dione], C(12)H(20)N(2)O(2)S(2), is slightly puckered. (I) and (II) contain the same hydrogen-bonded chain structure in which each mol­ecule is connected, via four N—H⋯O=C hydrogen bonds, to two other mol­ecules, resulting in a hydrogen-bonded chain displaying a sequence of R (2) (2)(8) rings. The same type of N—H⋯O=C hydrogen-bonded chain has previously been found in several 5,5-disubstituted derivatives of barbituric acid which are chemically closely related to (I) and (II).