Substituted indolizines and derivatives as CNS agents

A compound of formula (1):

• or a pharmaceutically acceptable salt thereof;
• wherein
• R is H, C1-C6 alkyl, C6-C10 aryl, 5 to 10 membered heteroaryl having 1 to 3 heteroatoms each independently selected from nitrogen, oxygen and sulfur, or —C(O)R′, wherein R′ is C1-C6 alkyl, C6-C10 aryl, or 5 to 10 membered heteroaryl having 1 to 3 heteroatoms each independently selected from nitrogen, oxygen and sulfur;
• R1 is H, C1-C6 alkyl, C3-C8 cycloalkyl, or C1-C6 fluoroalkyl;
• R2 is C1-C6 alkyl, C3-C8 cycloalkyl, C1-C6 fluoroalkyl, C6-C10 aryl, or 5 to 10 membered heteroaryl having 1 to 3 heteroatoms each independently selected from nitrogen, oxygen and sulfur;
• R3 is C3-C6 alkyl, C1-C6 alkyl-C3-C8 cycloalkyl, or C1-C6 fluoroalkyl;
• or alternatively R2 and R3 can be taken together with the carbon atoms to which they are attached to form a ring of 5-8 carbon atoms;
• R4, R5, R6, and R7 are each independently H, halogen, cyano, hydroxyl, carboxyl, C1-C6 alkyl, C1-C6 fluoroalkyl, C1-C6 alkoxy, C1-C6 fluoroalkoxy, C6-C10 aryl, C6-C10 aryloxy, 5 to 10 membered heteroaryl having 1 to 3 heteroatoms each independently selected from nitrogen, oxygen and sulfur, C2-C8 alkenyl, C2-C6 alkanoyl, C2-C6 alkanoyloxy, C2-C6 alkoxycarbonyl, carboxamido, C2-C6 alkanamido, C1-C6 alkanesulfonamido, amino, C1-C6 monoalkylamino, dialkylamino of 1 to 6 carbon atoms per alkyl moiety, C3-C8 cycloalkyl, or a 3 to 8 membered heterocycloalkyl having 1 to 3 heteroatoms each independently selected from nitrogen, oxygen and sulfur;
• R8 is H, C1-C6 alkyl, C3-C8 cycloalkyl, or C6-C10 aryl;
• wherein any cycloalkyl or heterocycloalkyl group is saturated or partially saturated, and any aryl, heteroaryl, cycloalkyl, or heterocycloalkyl group may optionally be substituted with 1 to 5 substituents independently selected from halogen, hydroxyl, C1-C6 alkyl, C1-C6 fluoroalkyl, C1-C6 alkoxy, and C1-C6 fluoroalkoxy.