Compound of formula I or formula I ': ** Formula ** or pharmaceutically acceptable salt thereof, wherein: Ar1 is a 5-6 membered aromatic monocyclic ring having 0-4 heteroatoms independently selected from nitrogen, oxygen or sulfur, wherein said ring is optionally condensed with a 5-12 membered, partially unsaturated or saturated, monocyclic or bicyclic aromatic ring, in which each ring contains 0-4 heteroatoms independently selected from nitrogen, oxygen or sulfur, in which Ar1 has m substituents, each independently selected from -WRW； W is a bond or is an optionally substituted C1-C6 alkylidene chain in which up to two methylene units of W are optionally and independently substituted by O, -CO-, -CS-, -COCO-, -CONR'-, - CONR'NR'-, -CO2-, -OCO-, -NR'CO2-, -O-, -NR'CONR'-, -C (O) NR'-, -OCONR'-, -NR'NR ' , -NR'NR'CO-, -NR'CO-, -S-, -SO, -SO2-, -NR'-, -SO2NR'-, NR'SO2- or -NR'SO2NR'-； RW is independently R ', halo, cyano, CF3, CHF2, OCHF2, Me, Et, CH (Me) 2, CHMeEt, n-propyl, t-butyl, OH, OMe, OEt, OPh, O-fluorophenyl, O- difluorophenyl, O-methoxyphenyl, O-tolyl, O-benzyl, SMe, SCF3, SCHF2, SEt, CH2CN, NH2, NHMe, N (Me) 2, NHEt, N (Et) 2, C (O) CH3, C ( O) Ph, C (O) NH2, SPh, SO2- (amino-pyridyl), SO2NH2, SO2Ph, SO2NHPh, SO2-N-morpholino, SO2-N-pyrrolidyl, N-pyrrolyl, N-morpholino, 1-piperidyl, phenyl, benzyl, (cyclohexyl-methylamino) methyl, 4-Methyl-2,4-dihydro-pyrazol-3-one-2-yl, benzimidazol-2-yl, furan-2-yl, 4-methyl-4H- [ 1,2,4] triazol-3-yl, 3- (4'-chlorophenyl) - [1,2,4] oxadiazol-5-yl, NHC (O) Me, NHC (O) Et, NHC (O) Ph or NHSO2Me； m is 0-5； k is 0-2； each R1 is independently -X-RX； X is a bond or is an optionally substituted C1-C6 alkylidene chain in which up to two methylene units of X are optionally and independently substituted by -CO-, -CS-, -COCO-, -CONR'-, -CONR ' NR'-, -CO2-, -OCO-, -NR'CO2-, -O-, -NR'CONR'-, -OCONR'-, -NR'NR ', -NR'NR'CO-, -NR 'CO -, -S-, -SO, -SO2-, -NR'-, -SO2NR'-, -NR'SO2- or -NR'SO2NR'-； RX is independently R ', halo, NO2, CN, CF
