R, is 3-pyridyl or 4-pyridyl, R 2 is C 1 ~C 12 -alkyl; C 3 - or C 4 -alkenyl; C 5 - or C 6 -cycloalkyl which may be substituted by C,- or C 2 -alkyl; pyridyl; pyridylmethyl; phenethyl cyanoalkyl having 1 or 2 carbon atoms; methoxyethyl; 1-methylmethoxypropyl; phenyl; phenyl which is substituted by one or more of C 1 ~C 4 -alkyl, C 1 ~C 4 -alkoxy, nitro, halogen, trifluoromethyl, allyl and methoxycarbonyl; benzyl; benzyl which is substituted by one or more of methyl, nitro, methoxy and chloro; a-methylbenzyl; C 1 ~C 6 -alkyl which is substituted by halogen when X is oxygen or C 2 - or C 3 -alkyl which is substituted by dimethylamino, furfuryl or thienylmethyl; R 3 is hydrogen, C 1 ~C 4 -alkyl, cyanomethyl, methoxycarbonylmethyl, or 1-propoxycarbonylmethyl.