A compound of the formula (I) ##STR1## wherein (1) when R.sub.1 is a C.sub.2-11 alkyl, a lower alkenyl, a lower alkynyl, a cycloalkyl, a lower alkoxyalkyl, an aralkyl which may be substituted, a lower haloalkyl or a 5 or 6 membered heterocycle;R.sub.2, R.sub.3 and R.sub.4 are the same or different, hydrogen, a halogen, cyano, nitro, amino, a lower alkyl, a lower haloalkyl, hydroxy, a lower alkoxy, an aryloxy, carboxy, or a lower alkoxycarbonyl;R.sub.5 is hydrogen, a halogen, a C.sub.1-11 alkyl, an aryl which may be substituted, an aralkyl which may be substituted;R.sub.6 is a C.sub.1-11 alkyl, a lower alkenyl, a lower alkynyl, a cycloalkyl, a lower alkoxyalkyl, an aryl which may be substituted, an aralkyl which may be substituted, a lower haloalkyl, or a 5 or 6 membered heterocycle; or R.sub.5 and R.sub.6 may be combined to form a group of --(CH.sub.2).sub.m -- (m is 3 or 4);(2) when R.sub.1 is an aryl which may be substituted;R.sub.2, R.sub.3, R.sub.4 and R.sub.5 have the same meanings as defined above; R.sub.6 is a C.sub.1-11 alkyl, a lower alkenyl, a lower alkynyl, a cycloalkyl, a lower alkoxyalkyl, an aralkyl which may be substituted, a haloalkyl or a 5 or 6 membered heterocycle, or R.sub.5 and R.sub.6 may be combined to form a group of --(CH.sub.2).sub.m -- (m is 3 or 4);(3) when R.sub.1 is methyl;R.sub.2, R.sub.3, R.sub.4 and R.sub.5 have the same meanings as defined above; R.sub.6 is a C.sub.2-12 alkyl, a lower alkenyl, a lower alkynyl, a cycloalkyl, a lower alkoxyalkyl, an aryl which may be substituted, an aralkyl which may be substituted, a lower haloalkyl or a 5 or 6 membered heterocycle or R.sub.5 and R.sub.6 may be combined to form a group of --(CH.sub.2).sub.m -- (m is 3 or 4); or(4) when R.sub.1 and R.sub.6 are methyl;R.sub.2, R.sub.3 and R.sub.4 have the same meanings as defined above; R.sub.5 is a halogen, a C.sub.1-11 alkyl, an aryl which may be substituted or an aralkyl which may be substituted, which is useful as herbicide.