Compounds of formula (I) and pharmaceutically acceptable salts thereof, wherein R1, R2, R3, R4, L1 and G1 are as defined in the specification, are useful in treating conditions or disorders prevented by or ameliorated by positive allosteric modulation of the γ-aminobutyric acid B (GABA-B) receptor. Methods for making the compounds are described. Also described are pharmaceutical compositions of compounds of formula (I), and methods for using such compounds and compositions.