6-substituted-s-triazolo[3,4-a]phthalazine derivatives

A s-triazolo[3,4-a]phthalazine having the formula ##STR160## wherein R represents phenyl, phenyl substituted with monohydroxy or from 1 to 3 substituents selected from (C.sub.1 -C.sub.6)alkyl, (C.sub.1 -C.sub.6)alkoxy, chloro, fluoro, bromo, phenyl, amino, mono- and di-(C.sub.1 -C.sub.4)-alkylamino, (C.sub.2 -C.sub.4)alkanoylamino, piperidino, cyano, nitro, trifluoromethyl, carboxy, and carbamyl with the proviso that the phenyl group cannot be substituted with mixtures of amino and nitro, alkanoylamino and alkylamino, or hydroxy and alkoxy groups, R is carbo(C.sub.1 -C.sub.4)-alkoxy, chloro, (C.sub.1 -C.sub.4 alkylsulfinyl, (C.sub.1 -C.sub.4)-alkylsulfonyl, a substituted amino group of the formula ##STR161## wherein R.sub.4 and R.sub.5, each independently, represents (C.sub.1 -C.sub.4)alkyl, (C.sub.2 -C.sub.4)alkyl substituted with one or two groups independently selected from hydroxy, (C.sub.1 -C.sub.4)alkoxy, halogen, carboxy, cyano, aminocarbonyl, mono- or di-(C.sub.1 -C.sub.4)alkylaminocarbonyl, (C.sub.1 -C.sub.4)alkoxycarbonyl, (C.sub.1 -C.sub.4)alkoxythiocarbonyl and (C.sub.1 -C.sub.4)alkyl-thiocarbonyl, or R.sub.4 and R.sub.5 independently are phenyl-(C.sub.1 -C.sub.4)alkyl or substituted phenyl(C.sub.1 -C.sub.4)alkyl wherein the alkyl portion as well as the phenyl portion may be substituted as defined above, or R.sub.4 and R.sub.5 taken together with the adjacent nitrogen atom may represent a saturated 4, 5 or 6-membered ring selected from the group consisting of azetidine, pyrrolidine, piperidine, piperazine and morpholine, and optionally bears one or two substituents independently seleted from (C.sub.1 -C.sub.4)alkyl, phenyl, hydroxy, and carbo(C.sub.1 -C.sub.4 alkoxy, or R represents an alkoxy or cycloalkoxy group of formula --OR.sub.6 wherein R.sub.6 stands for a (C.sub.1 -C.sub.6)alkyl, substituted with one or two groups independently selected from hydroxy, amino, mono- or di-(C.sub.1 -C.sub.4)alkylamino, (C.sub.1 -C.sub.4)alkoxy, halogen, oxo, carboxy, aminocarbonyl, mono- or di-(C.sub.1 -C.sub.4)alkylamino, (C.sub.1 -C.sub.4)alkoxycarrbonyl, (C.sub.1 -C.sub.4)alkoxythiocarbonyl and (C.sub.1 -C.sub.4)alkylthiocarbonyl, or R.sub.6 is a saturated 4, 5 or 6-membered ring selected from the group consisting of azetidine, pyrrolidine, piperidine, piperazine and morpholine, and optionally bears one or two substituents independently selected from (C.sub.1 -C.sub.4)alkyl, phenyl, hydroxy, and carbo- (C.sub.1 -C.sub.4)alkoxy, or R.sub.6 is a (C.sub.5 -C.sub.8)cycloalkyl group optionally substituted with one or more hydroxy and (C.sub.1 - C.sub.4)alkoxy groups;

• R.sub.1 is selected from halogen, hydroxy, (C.sub.1 -C.sub.4)alkylthio, (C.sub.1 -C.sub.4)alkylsulfinyl, (.sub.1 -C.sub.4)alkylsulfonyl, phenyl, phenyl substituted as above, a substituted amino group of the formula ##STR162## wherein R.sub.7 or R.sub.8 are as defined above for R.sub.4 and R.sub.5, and an alkoxy or cycloalkoxy group of formula --OR.sub.9 wherein R.sub.9 is defined as R.sub.6 above;
• R.sub.2 is hydrogen;
• and
• R.sub.3 represents hydrogen, halogen, (.sub.1 -C.sub.4)alkyl, (C.sub.1 -C.sub.6)alkoxy and nitro;
• with the proviso that when R.sub.3 is hydrogen and R.sub.1 is chloro, R cannot be hydrogen, halogen, methyl, phenyl or 4-nitrophenyl, and that when R.sub.1 is hydroxy, R must be different from phenyl;
• with the further proviso that when R and/or R.sub.1 are --OR.sub.6 or --OR.sub.9, respectively, wherein the R.sub.6 and/or R.sub.9 are a saturated heterocyclic ring as above defined, the heteroatom of said heterocycle cannot be directly linked to the oxygen atom.