Treatment of (2) with benzenesulphonic acid in ethanol under reflux provides no evidence for clean isomerisation to (3), but leads instead to a mixture of several other products. The absence of unsaturated thioketone would be in keeping with the pattern seen for thietes obtained from thioketones, where only those derived from bis-heteroatom-substituted alkynes undergo ringopening of this kind; the related oxetes obtained from ketones and ...