Gamma-secretase inhibitors

A compound of formula I:

• wherein n is 0 or 1;
• X completes a 5- or 6-membered heteroaromatic ring bearing the group Ar as a substituent, and also the group R5 as a substituent when n is 1;
• R5 represents a hydrocarbon group of 1-5 carbon atoms which is optionally substituted with up to 3 halogen atoms;
• Ar represents phenyl or 6-membered heteroaryl, either of which bears 0-3 substituents independently selected from halogen, CF3, CHF2, CH2F, NO2, CN, OCF3, C1-6alkyl and C1-6alkoxy;
• Y represents a bond or NR3;
• R1 represents H, or when Y represents NR3, R1 and R3 may together represent —CH2—;
• R2 represents a hydrocarbon group of 1-10 carbon atoms which is optionally substituted with up to 3 halogen atoms, or heteroaryl of 5 or 6 ring atoms optionally bearing up to 3 substituents independently selected from halogen, CF3, CHF2, CH2F, NO2, CN, OCF3, C1-6alkyl and C1-6alkoxy;
• or when Y represents NR3, R2 and R3 together may complete a heterocyclic ring of up to 6 members which optionally bears up to 3 substituents independently selected from halogen, CF3, CHF2, CH2F, NO2, CN, OCF3, C1-6alkyl and C1-6alkoxy;
• R3 represents H or C1-4alkyl, or together with R1 represents —CH2—, or together with R2 completes a heterocyclic ring as defined above;
• and
• R4 represents halogen or C1-4alkyl;
• or a pharmaceutically acceptable salt thereof.