Compounds of formula (I) and salts thereof are provided: wherein n is 0, 1, 2 or 3; R1 is selected from phenyl and pyridyl, each of which is optionally substituted by one or two groups independently selected from C1-4alkyl and halogen; and R2 is selected from H and CH3 when n is 1 and R2 is H when n is 2 or 3. Processes for preparation, pharmaceutical compositions, N and uses thereof as a medicament, for example in the treatment of a disease or condition mediated by a reduction or imbalance in glutamate receptor function, such as schizophrenia or cognition impairment, are also disclosed.