The invention provides compounds of the formula (1) or salts or tautomers thereof; wherein: Q is SO or SO2; n is 1 or 2; R1 is selected from hydrogen and a non-aromatic C1-6 hydrocarbon group; R2 and R3 are independently selected from hydrogen and a C1-6 hydrocarbon group; or R2 and R3 together with the carbon atom to which they are attached form a carbonyl group (C=O), a cyclopropane-1,1-diyl group or a cyclobutane-1,1-diyl group; or R together with R2 forms a C2-4 alkylene linker which is optionally substituted with one or more substituents selected from a C1-4 hydrocarbon group, halogen, hydroxy and amino; R4 and R5 are independently selected from hydrogen and a non-aromatic C1-6 hydrocarbon group; or R4 and R5 together with the carbon atom to which they are attached form a cyclopropane-1,1-diyl group or a cyclobutane-1,1-diyl group; and Ar1 is selected from phenyl, thiophenyl and furanyl,each being optionally substituted. The compounds are useful in medicine, for example in the treatment of diseases, such as cancers.