Heterocyclic fused phenanthrolinone M1 receptor positive allosteric modulators

A compound of formula (I):

• or a pharmaceutically acceptable salt thereof, wherein
• X represents —CH, or —O;
• R represents C6-10 aryl or C5-10 heterocyclyl;
• wherein said aryl and heterocyclyl is optionally substituted with one or more of RX
• RX represents:
• (a) halogen,
• (b) hydroxy,
• (c) —O—C1-6 alkyl, said alkyl optionally substituted with 1 to 3 groups of halo;
• (d) —C1-6 alkyl, said alkyl optionally substituted with 1 to 3 groups of halo;
• (e) cyano,
• (f) NRARB
• (g) —C(═O)—RC,
• (h) —S(O)n—RC;
• or
• (i) C5-10 heterocyclyl, said heterocyclyl optionally substituted with 1 to 3 groups of RC;
• RA and RB are independently selected from the group consisting of
• (i) hydrogen,
• (ii) —C1-6 alkyl,
• or RA and RB are linked together with the nitrogen to which they are both attached to form a 2-6 membered carbocyclic ring, wherein one or two of the ring carbon atoms is optionally replaced by a nitrogen, oxygen or sulfur, and the carbocyclic is optionally substituted with one or more C1-6 alkyl,
• RC is selected from the group consisting of
• (i) hydrogen, or
• (ii) —C1-6 alkyl, and
• n is 0, 1 or 2.