As part of our ongoing research into the antileishmanial properties of amidoxime derivatives, we report a preliminary assessment of the antiparasitic properties of a novel compound, diethyl (5-benzyl-2-(4-(N′-hydroxycarbamimidoyl)phenyl)-5-methyl-4,5-dihydrofuran-3-yl)phosphonate. This compound was evaluated in vitro for the first time against the promastigote form of Leishmania amazonensis. Compounds containing both amidoxime and phosphonyl functional groups in dihydrofuran scaffolds are relatively rare, despite the extensive study of this heterocycle in various biological applications. Therefore, this work makes a valuable contribution to the fight against Leishmania spp. as a neglected disease. The cyclized 4,5-dihydrofuran intermediate scaffold was obtained via a three-step synthetic route that had previously been developed for accessing other derivatives, including the sulfone moiety. This synthesis was performed using a manganese-based free radical oxidative method under microwave irradiation. The intermediary 4,5-dihydrofuran, which included a nitrile group, tolerated the subsequent reaction with hydroxylamine hydrochloride, resulting in the formation of the target product. The target compound showed moderate activity in vitro against the promastigote form of L. amazonensis (IC50 = 91.1 µM).