Introduction/Background: Long-chain alkenyl aldehydes constitute a significant class of insect sex pheromone components. Usually, these compounds are typically synthesized by oxidizing their corresponding alkenyl alcohols. However, this transformation presents challenges. This study aims to develop an efficient and cost-effective method for producing longchain alkenyl aldehyde insect sex pheromones for field trials. Materials and Methods: This paper utilizes copper bromide (CuBr) as the catalyst, 2,2'- bipyridine (BPY) as the ligand, N-methylimidazole (NMI) as the base, and acetonitrile as the solvent. Air and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (HO-TEMPO) effectively oxidize a variety of long-chain alkenyl alcohols. Results: This method utilizes CuBr (0.05 equiv.) as the catalyst, BPY (0.05 equiv.) as the ligand, NMI (0.07 equiv.) as the base, and acetonitrile as the solvent. Under these conditions, air and HO-TEMPO (0.05 equiv.) effectively oxidize a variety of long-chain alkenyl alcohols, including those with different chain lengths and configurations, to the corresponding aldehydes at room temperature. Discussion: To identify optimal reaction conditions, we systematically investigated the effects of various parameters, including the type of base, copper catalyst, solvent and ligand. The choice of base significantly impacted the reaction yield, and NMI and DMAP performed well. CuBr was chosen as the optimal copper catalyst, acetonitrile was identified as the optimal solvent, and BPY was identified as the optimal ligand. Conclusion: This method demonstrated broad substrate scope, successfully oxidizing various long-chain alkenyl alcohols with diverse chain lengths and configurations to their corresponding aldehydes, insect sex pheromones, in yields ranging from 72% to 88%. The field test demonstrated that the sex pheromones prepared by our method exhibited very potent trapping efficacy against the rice stem borer moth (C. suppressalis Walker).
Wang et al. (Tue,) studied this question.