This invention is directed to compounds of the following formula: wherein when a is 0, b is 1 or 2; when a is 1, b is 1, m is from 0-3, X is O or S, Y is halogeno, R1 is hydrogen C1-4 alkyl, R2 is hydrogen, C1-4 alkyl, or optionally substituted propargyl and R3 and R4 are each independently hydrogen, C1-6 alkyl, C6-12 aryl, C6-12 aralkyl each optionally substituted. This invention is also directed to the use of these compounds for treating depression, Attention Deficit Disorder (ADD), Attention Deficit and Hyperactivity Disorder (ADHD), Tourette's Syndrome, Alzheimer's Disease and other dementia's such as senile dementia, dementia of the Parkinson's type, vascular dementia and Lewy body dementia. This invention is further directed to a pharmaceutical composition comprising a therapeutically effective amount of the above-defined compounds and a pharmaceutically acceptable carrier.