PURPOSE: To obtain a new compound useful for a herbicide having a wide herbicidal spectrum.

CONSTITUTION: The compound of formula I [R2 is furyl, phenyl, naphtyl, pyridil or the like; R3 is (halo) 1-3C alkyl, 3-4C alkenyl, 3-6C alkynyl or the like; R5 is H, 1-5C alkyl, 3-6C alkenyl, 2-6C alkynyl or the like; R6 is H, halo, 1-8C alkyl, 2-6C alkenyl or the like; X is O or S], e.g. 5.6-diethyl-2-phenyl-3- propargyl-4(3H)-pyrimidinone, is obtained by reacting e.g. the compound of formula II with the β-ketoester of formula III (R is alkyl or the like).