Apart from adjusting TeA's 5-position, there have also been modifications made at the 3-position. For example, in 2005, Zhu [
113] modified the pyrrolidone by introducing a substituted benzene ring into its 3-position. Compound
91 (Fig. S2) was found to be more effective in inhibiting the growth of
Brassica campestris (
B. campestris) than the positive control drug sulcotrione, and it also showed good herbicidal activity against monocotyledonous plants such as
E. crusgalli and
Digitaria sanguinalis (
D. sanguinalis). The structure-activity relationship indicates that substituents on the benzene ring that donate electrons are more effective in inhibiting growth. By replacing the benzyl group on N with isopropyl, the resulting herbicide showed a 100-fold increase in activity against
E. crusgalli compared to compound
91. The substituents on the benzene ring at the 3-position were altered. Electron-donating substituents showed better activity, which may be attributed to their ability to facilitate the formation of enol isomers, thus increasing the likelihood of the compound binding to the 4-hydroxyphenylpyruvate dioxygenase (HPPD) center. Additionally, these compounds exhibited growth inhibition and bleaching properties, with the benzene ring effectively preserving this conjugated system. Compounds
92a-92b (Fig. S2) have superior herbicidal activity compared to sulcotrione and completely eradicate monocotyledonous plants such as
E. crusgalli and
D. sanguinalis. Compound
92b has a selectivity of 187.5 g/ha for corn and soybean before sprouting, and a control effect of 93% [
113,
114]. To further explore the variety of this compound, Zhu replaced phenyls with substituted heterocycles [
115]. Compounds
92c-92d (Fig. S2) were synthesized, leading to a notable enhancement in the inhibition rate of rapeseed; however, they did not show a significant impact on the growth inhibition of
E. crusgalli. This shows that the introduction of larger groups is advantageous for suppressing the growth of dicotyledonous plants, but does not yield the same results for inhibiting monocotyledonous plants. When substituted with a thiophene ring
(92c) and a pyridine ring (
92d) (Fig. S2), it showed good inhibition activity against
E. crusgalli at 10 mg/L, with 52% and 60%, respectively. Subsequently employing the principle of biological equivalence, the indole ring was introduced into the 3-position of pyrrolidone [
116]. At 100 mg/L, compound
93 (Fig. S2) exhibited a certain degree of herbicidal activity against
E. crusgalli and
B. campestris. Subsequently, by replacing the 3-position with cyclopropane, compound
94 (Fig. S2) showed the most effective inhibitory rate of 89% against
E. crusgalli at 100 mg/L, and it also showed good activity against
B. campestris. In 2012, Liu introduced cyano, sulfonyl, and amino groups to the 3-position of the 2, 4-pyrrolidinedione ring. The cyano compound
95 (Fig. S2) and the sulfonyl compound
96 (Fig. S2) were synthesized using the Dieckmann reaction, while the amino compound
97 (Fig. S2) was formed from 3-carboxylate derivatives with the aid of microwave technology. Although no herbicidal activity was observed, compound
97 had a bleaching effect on weed leaves, suggesting a possible binding with HPPD. Compound
95 exhibited some insecticidal activity. Following this, a hydrazine group was introduced at the 3-position [
117]. In comparison to TeA, the 3-hydrazido compounds
98a-98e showed relatively better herbicidal activities. In particular,
N-arylcarbonyl compounds
98b-98c (Fig. S2) showed a 55% inhibition rate on
Amaranthus retroflexus (
A. retroflexus) weed control, which was greater than that of the hydrophilic
N-acetyl compound
98a (Fig. S2), the
N‑
tert-butoxycarbonyl compound
98e (Fig. S2), and the ethoxycarbonyl compound
98d (Fig. S2). The 3-hydrazono compounds
99a-99e (Fig. S2), based on 3-hydrazine, showed good herbicidal activity against dicotyledonous plants such as
B. campestris and
A. retroflexus. However, the structure-activity relationship of these compounds was the opposite of that of compounds
98a-98e. The activity of compounds
99b-99c, which have aromatic carbonyl groups on nitrogen, was weaker than that of the
N-acetyl compound
99a and the
N-alkoxycarbonyl compounds
99d-99e [
118]. In 2009, Zhu introduced oxime ether structure for TeA, where they substituted the 1-position with a phenyl group. Compound
100 (Fig. S2) was found to be effective in controlling the growth of
B. campestris and
E. crusgalli. At 100 mg/L, compound
100 showed an inhibition rate of 66.2% against
B. campestris [
119]. Surprisingly, compound
101 (Fig. S2) features an oxime ether structure at the 3-position and a cycloalkyl group at the 1-position. Despite this difference, it displayed inhibitory rates exceeding 70% against
B. campestris at the same concentration. In both cases, the inhibitory rates against
B. campestris were found to be over 80% [
120]. The change in substituents improved the derivatives activity. Simultaneously, Wang
et al. [
121] added amines to the 3-position of 2, 4-pyrrolidinedione. At 100 mg/L, compound
102 (Fig. S2) was able to inhibit the growth of
E. crusgalli and
B. campestris by 94.4% and 67.4%, respectively. In 2011, Si
et al. [
122] uncovered a novel semicarbazide structural unit at the 3-position of 2, 4-pyrrolidinedione. Compound
103 (Fig. S2) showed an inhibitory activity of 86% against
B. campestris. The group attached at the 3-position is typically the one capable of preserving the pyrrolidone conjugate system. Examples include the ketone structure with the alkenyl group attached and the enol group connected to the carbonyl group, both of which contribute to the continuation of the pyrrolidone conjugate structure. The presence of an electron-withdrawing group is crucial in this process.