Substituted pyrimido[1,2-b]pyridazines as positive allosteric modulators of the muscarinic acetylcholine receptor M4

A compound of formula (Ib):

• or a pharmaceutically acceptable salt or stereoisomer thereof,
• wherein:
• R1 is H, C1-C4 alkyl, C1-C4 haloalkyl, C1-C3 alkylene-ORa, C1-C3 alkylene-C3-C6 cycloalkyl, or C3-C6 cycloalkyl;
• Ra is C1-C4 alkyl, C1-C4 haloalkyl, or C3-C6 cycloalkyl;
• R2 is H, C1-C4 alkyl, C1-C3 alkylene-ORb, NHRb, NRbRb, ORb, or C3-C6 cycloalkyl;
• R7 is H, halo, C1-C4 alkyl, NRbRb, or C3-C6 cycloalkyl;
• each R3 is independently C1-C4 alkyl, C1-C4 haloalkyl, or C3-C6 cycloalkyl;
• or
• two Rb, taken together with the nitrogen heteroatom to which they are attached, form a monocyclic 4- to 7-membered heterocyclyl;
• R3 is H, C1-C4 alkyl, C1-C3 alkylene-ORc, or C3-C6 cycloalkyl;
• Rc is C1-C4 alkyl, C1-C4 haloalkyl, or C3-C6 cycloalkyl;
• R4 is halo or C1-C4 alkyl;
• X is CR5a;
• R5a is H, halo, or C1-C4 alkyl;
• R5b is halo, CN, C1-C2 alkyl, C1-C2 fluoroalkyl, OC1-C2 alkyl, OC1-C2 fluoroalkyl, or C3-C6 cycloalkyl;
• n is 0;
• and
• o is 0 or 1.