Synthesis and crystal structures of 3-hy­droxy-2,4-dimethyl-2H-thio­phen-5-one and 3-hy­droxy-4-methyl-2H-thio­phen-5-one

The structures of two hy­droxy-thio­phenone derivatives related to the anti­biotic thiol­actomycin are presented. These are the racemic 3-hy­droxy-2,4-dimethyl-2H-thio­phen-5-one, C6H8O2S, and 3-hy­droxy-4-methyl-2H-thio­phen-5-one, C5H6O2S. The main structural feature of both compounds is C(6) hydrogen-bonded chains formed between the OH and C=O groups. In achiral C5H6O2S, these chains propagate only by translation, corresponding to x + 1, y, z + 1. However, in contrast, for racemic C6H8O2S the hydrogen-bonded chains propagate through a −x + Unlabelled Image, y + Unlabelled Image, z operation, giving chains lying parallel to the crystallographic b-axis direction that are composed of alternate R and S enanti­omers. The crystals of 3-hydroxy-4-methyl-2H-thiophen-5-one were found to be twinned by a 180° rotation about the reciprocal 001 direction. In the final refinement the twin ratio refined to 0.568 (2):0.432 (2).