tricyclic isoindole derivatives characterized by having a 1 , 2 , 3 , 4 , 6 , 10b - hexahydropyrazino ] 2 , 1 - a ] isoindole or 1 , 3 , 4 , 10b - tetrahydropyrimidoisoindol - 6 - one nucleus are disclosed . the foregoing compounds are useful antihypertensive agents . claimed compounds include those of the formula ## str1 ## in which r 3 and r 4 each is hydrogen , lower alkoxy , lower alkyl , trifluoromethyl , halo or hydroxy , or r 3 and r 4 together form an och 2 o chain ; and r 14 and r 15 each is hydrogen or lower alkyl .