Imidazole compounds exhibit excellent antifungal activity. For instance, compounds
11–13 (
Fig. 8) demonstrate strong inhibitory effects against
Penicillium digitatum (
P. digitatum), with median inhibition concentration (IC
50) values of 4.14, 5.06, and 7.12 mg/L, respectively. SAR analysis indicates that the R
1 position-substituted quinazoline moiety of imidazole exhibits favorable fungicidal activity. Maintaining a phenyl group at the R
3 position within the quinazoline structure further enhances fungicidal potency [
54]. The chiral isomeric imidazole compounds
14 and
15 exhibit excellent broad-spectrum antifungal activities against
Botrytis cinerea (
B. cinerea),
Rhizoctonia cerealis (
R. cerealis), and
Sclerotinia sclerotiorum (
S. sclerotiorum) with median effective concentration (EC
50) values of
14 (4.65, 0.50, and 3.99 mg/L) and
15 (3.14, 0.31, and 0.33 mg/L), respectively. Compound
15 exhibits potent fungicidal activity by inhibiting
B. cinerea mycelial growth and spore germination, as well as disrupting cell structure through impaired cell wall formation [
55]. Several imidazoles exhibit excellent
in vivo activity. In plant bioassays experiments, compounds
16, 17, and
18 demonstrated superior efficacy against
Alternaria solani (
A. solani),
Botryotinia fuckeliana (
B. fuckeliana),
Erysiphe necator (
E. necator) at 60 mg/L (inhibition rates exceeding 90%) [
56]. Methyl substitution at the R
5 position of the imidazole ring confers potent fungicidal activity; for instance, compound
19 exhibits fungicidal activity against
Rhizoctonia solani (
R. solani) with an EC
50 of 2.63 mg/L [
57]. Furthermore, when the imidazole R
5 position is methylated, the introduction of fluorine or chlorine atoms onto the benzene ring attached to the imidazole R
1 position simultaneously exhibits good fungicidal activity. For instance, compounds
20 and
21 exhibited outstanding activity against
B. cinerea and
Uncinula necator (
U. necator) (with EC
80 values of 2, 1 and 1, 1 mg/L, respectively). Tubulin polymerization assays revealed that compounds
20 and
21 exert their potent fungicidal activity by promoting fungal tubulin polymerization and subsequently disrupting microtubule dynamics [
58]. When a chlorine atom is introduced at the R
4 position of the imidazole ring, it exhibits good fungicidal activity against
R. solani. At a concentration of 50 mg/L, compound
22 demonstrated a 90.3% inhibition rate against
R. solani [
59]. Interestingly, when an ester group substitution is introduced at the R
1 position of the imidazole ring, good
in vivo activity is observed. For example, compound
23 exhibited good
in vivo activity against
B. cinerea on tomato at a concentration of 200 mg/L (with protective and curative activities of 58.4% and 48.7%, respectively) [
60]. Imidazolone compounds exhibit excellent and broad-spectrum fungicidal activities. For instance, compound
24 demonstrated good fungicidal activity against
S. sclerotiorum (EC
50 = 24.37 mg/L), and compound
25 showed good fungicidal activity against
Phytophthora capsici (
P. capsici) (EC
50 = 28.68 mg/L) [
61]. Additionally, compounds
26 and
27 exhibited favorable fungicidal activity against
A. solani (EC
50 values of 4.14 and 3.27 mg/L, respectively), while compound
28 demonstrated an EC
50 value of 3.23 mg/L against
S. sclerotiorum [
62]. The introduction of trifluoromethyl groups on the benzene ring connected to the imidazole ring at the R
2 position enhances fungicidal activity. Compound
29 exhibited good inhibitory activity against
S. sclerotiorum and
P. capsici (EC
50 values of 6.50 and 7.51 mg/L, respectively). Scanning electron microscopy revealed that compound
29 impaired the cell walls and vacuoles of
P. capsici hyphae, leading to altered membrane structures and thereby demonstrating its excellent fungicidal activity [
63]. The introduction of a triazole group at the R
4 position of imidazole demonstrated good fungicidal activity. For example, compounds
30 and
31 exhibited inhibitory activity against
R. solani at 30 mg/L (inhibition rates of 78% and 88%, respectively) [
64]. SAR analysis indicates that maintaining the imidazolidone skeleton while introducing a benzylamine substitution at the R
2 position of the imidazole ring yields excellent fungicidal activity. In the future, retaining this core structure while introducing different substituents at the R
1 and R
4 positions of the imidazole ring may lead to the discovery of superior novel fungicides.