The present invention provides compounds of Formula (I): and pharmaceutically acceptable salts thereof wherein the variables R1, R2, R3, R4, R5, a and A are as defined herein; processes for the preparation of; intermediates used in the preparation of; and compositions containing such compounds or salts, and their uses for treating D3-mediated (or D3-associated) disorders including, e.g., substance addiction, substance abuse, schizophrenia (e.g., its cognitive symptoms), cognitive impairment (e.g., cognitive impairment associated with schizophrenia, AD or PD), Parkinson's disease, mania, anxiety, impulse control disorders, sexual disorders and depression.