Abstract: Disclosed are pyrimidine derivatives represented by general formula (I) ##STR1## wherein X represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a haloalkyl group or a cyano group; Y.sup.1 represents an alkyl group, a cyanoalkyl group, an alkoxy group, an alkenyl group substituted with a hydroxy group and a halogen atom, an alkynyl group which may be substituted with a hydroxy group, a methylamino group, an alkoxyalkyloxy group, an alkylthioalkyl group or a group of the formula --CH.sub.2 OR.sup.1 where R.sup.1 represents a hydrogen atom, an alkyl group, an alkenyl group or an alkynyl group; Y.sup.2 represents a halogen atom, an alkyl group or a haloalkyl group; R represents a hydrogen atom, an alkyl group, a nitroso group, an alkoxyalkyl group, an alkoxyalkyloxyalkyl group, an alkenyl group, an alkynyl group, a formyl group or an alkylthioalkyl group, with the proviso that (a) when Y.sup.1 represents an alkynyl grop or when Y.sup.1 represents an alkoxy group and Y.sup.

Abstract: A new class of 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives were synthesized. They are useful as agricultural-horticultural fungicides.

Abstract: A class of novel 5H-1,3,4-thiadiazolo[3,2-a]-pyrimidin-5-one derivatives are disclosed. These compounds exhibit remarkable fungicidal activities for pathogenic fungi of cucumber gray mold, cucumber downy mildew. Alternaria sooty spot of Chinese mustard, apple Alternaria leaf spot, pear black spot, rice blast, tomato late blight, etc.

Abstract: A class of novel 5H-1,3,4-thiadizaolo[3,2-a]pyrimidin-5-one derivatives are disclosed. These compounds exhibit remarkable fungicidal activities for pathogenic fungi of cucumber gray mold, cucumber downy mildew, Alternaria sooty spot of Chinese mustard, apple Alternaria leaf spot, pear black spot, rice blast, tomato late blight, etc.

Abstract: It is disclosed that a class of 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives exhibit remarkable fungicidal activities for cucumber gray mold, cucumber downy mildew, Alternaria sooty spot of Chinese mustard, rice blast, etc.