Negative allosteric modulators of metabotropic glutamate receptor 2

A compound of formula (I), or a pharmaceutically acceptable salt thereof,

• wherein:
• R1, at each occurrence, is independently hydrogen, fluoro, or C1-4alkyl;
• R2 is hydrogen or C1-6alkyl;
• R3 is a 6- to 12-membered aryl or 5- to 12-membered heteroaryl containing 1-3 heteroatoms independently selected from the group consisting of N, O, and S, wherein R3 is unsubstituted or substituted with 1, 2, 3, or 4 substituents independently selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, OH, —OC1-4alkyl, and —OC1-2haloalkyl;
• R4 is G4, —C1-4alkylene-G4, Cy, or —C1-4alkylene-Cy;
• G4 is a 6- to 12-membered aryl or 5- to 12-membered heteroaryl, wherein G4 is unsubstituted or substituted with a first substituent selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, oxo, —OR4a, —N(R4a)2, —N(R4a)C(O)R4a, —N(R4a)SO2R4b, —C(O)N(R4a)2, —SO2N(R4a)2, —SO2R4b, —C1-4alkylene-OH, G4a, and —C1-4alkylene-G4a, and optionally further substituted with 1-3 substituents independently selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, —OC1-4alkyl, and —OC1-2haloalkyl;
• R4a, at each occurrence, is independently hydrogen, C1-4alkyl, C1-2haloalkyl, G4a, or —C1-4alkylene-G4a;
• R4b is C1-4alkyl, C1-2haloalkyl, G4a, or —C1-4alkylene-G4a;
• G4a is a phenyl, C3-6cycloalkyl, 5- to 6-membered heteroaryl containing 1-3 heteroatoms, or 4- to 6-membered heterocyclyl containing 1-2 heteroatoms, the heteroatoms in the heteroaryl and heterocyclyl being independently selected from the group consisting of O, N, and S, wherein G4a is optionally substituted with 1-4 substituents independently selected from the group consisting of C1-4alkyl, C1-2fluoroalkyl, halogen, cyano, oxo, OH, and —OC1-4alkyl;
• Cy is a C3-6carbocyclyl or a 4- to 6-membered heterocyclyl containing 1-2 heteroatoms independently selected from the group consisting of N, O, and S, wherein Cy is optionally substituted with a first substituent selected from the group consisting of C1-4alkyl, C1-2fluoroalkyl, halogen, oxo, OH, —OC1-4alkyl, G4a, and —C1-4alkylene-G4a, and optionally further substituted with 1-3 substituents independently selected from the group consisting of C1-4alkyl, C1-2fluoroalkyl, and halogen;
• and
• R5 and R6 are each independently hydrogen, C1-4alkyl, halogen, cyano, C1-2haloalkyl, —OC1-4alkyl, or —OC1-2haloalkyl.