A compound represented by the formula (I) or a salt thereof:
wherein a ring Z is a 5 to 6-membered heteroaromatic ring having one or two heteroatoms in the ring; X1 is a hydrogen atom, a hydroxy group, a hydroxy C1-6 alkyl group, -B(OH)2, a boronate ester group, a cyclic boronate ester group, a boranyl group, a cyclic boranyl group, -BF3Mn1, -Sn(R12)(R13)(R14), a leaving group, a carboxy group, a formyl group, or -NR16R17; and X2 is a hydrogen atom or -CO2R18.
A compound represented by the formula (I) or a salt thereof:
wherein a ring Z is a 5 to 6-membered heteroaromatic ring having one or two heteroatoms in the ring; X
1
is a hydrogen atom, a hydroxy group, a hydroxy C
1-6
alkyl group, —B(OH)
2
, a boronate ester group, a cyclic boronate ester group, a boranyl group, a cyclic boranyl group, —BF
3
M
n1
, —Sn(R
12
)(R
13
)(R
14
), a leaving group, a carboxy group, a formyl group, or —NR
16
R
17
; and X
2
is a hydrogen atom or —CO
2
R
18
.