This invention provides compounds of the formula: wherein R1 and R2 are each, independently, H, alkyl, cycloalkyl, —CH2-cycloalkyl, alkoxy, halogen, fluorinated alkyl, —CN, —NH—SO2-alkyl, —SO2—NH-alkyl, alkyl amide, amino, alkylamino, dialkylamino, fluorinated alkoxy, acyl, or phenoyl or thiophenoyl; R3 and R4 are each, independently, H, alkyl or cycloalkyl; R5 is H or alkyl; R6 is H or; and the dashed line indicates an optional double bond; or a pharmaceutically acceptable salt thereof, and pharmaceutical compositions and methods utilizing these compounds for the treatment or prevention of disorders including obsessive-compulsive disorder, depression, anxiety, generalized anxiety disorder, schizophrenia, migraine, sleep disorders, eating disorders, obesity, epilepsy, and spinal cord injury.