N-aroyl cyclic amines as orexin receptor antagonists

A compound of formula (I):

• wherein:
• X is O, CR7R8, NH or bond;
• R1 and R2 are both hydrogen, both optionally substituted (C1-4)alkyl, or are together with the carbon to which they are attached form a (C3-6)cycloalkyl ring or a 4- to 6-membered heterocyclyl ring.
• R3 and R4 are both hydrogen, both optionally substituted (C1-4)alkyl, or are together with the carbon to which they are attached form a (C3-6)cycloalkyl ring or a 4- to 6-membered heterocyclyl ring;
• R7 and R8 are both hydrogen, both optionally substituted (C1-4)alkyl, or are together with the carbon to which they are attached form a (C3-6)cycloalkyl ring or a 4- to 6-membered heterocyclyl ring;
• provided that one pair of R1 and R2, R3 and R4, R7 and R8 are both optionally substituted (C1-4)alkyl, or are together with the carbon to which they are attached form a (C3-6)cycloalkyl ring or a 4- to 6-membered heterocyclyl ring and the remaining groups are hydrogen;
• R5 is hydrogen, optionally substituted (C1-4) alkyl, or optionally substituted (C1-4)alkylCO;
• Ar1 is an optionally substituted aryl, an optionally substituted mono or bicyclic heteroaryl group containing up to 3 heteroatoms selected from N, O and S;
• Ar2 represents phenyl or a 5- or 6-membered heterocyclyl group containing up to 3 heteroatoms selected from N, O and S, wherein the phenyl or heterocyclyl group is substituted by R6 and further optional substituents;
• or Ar2 represents an optionally substituted bicyclic aromatic or bicyclic heteroaromatic group containing up to 4 heteroatoms selected from N, O and S;
• R6 represents hydrogen, optionally substituted(C1-4 )alkoxy, halo, cyano, optionally substituted(C1-6)alkyl, optionally substituted phenyl, or an optionally substituted 5- or 6-membered heterocyclyl group containing up to 4 heteroatoms selected from N, O and S;
• or a pharmaceutically acceptable salt thereof.