Synthesis and herbicidal and fungistatic evaluation of Passerini adducts bearing phenoxyacetic moieties

Abstract

A new idea for the modification of a carboxylic group in phenoxyacetic herbicides is proposed. Common herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA), and their chalcogen analogs (arylthio and arylselenyl fragments instead of a phenoxy one) were used as carboxylic components in the tricomponent Passerini reaction. Cyclohexyl isocyanide and 4-isocyano-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO-NC) were used as isocyanides. Acetone, acetaldehyde and formaldehyde were used as carbonyl components. Passerini adducts 4a–4L were obtained in yields of 32–59%. The structures of the Passerini adducts were determined using spectroscopic methods: MS, HR MS, 1H NMR, 13C NMR, 77Se NMR (if appropriate) and IR spectra (MS, HR MS, IR for the nitroxides 4k and 4L). The herbicidal activity of the Passerini adducts synthesized (4a–4L) was tested against ten weed species (at 2 kg/ha using 2,4-D and MCPA as a control). 100% herbicidal post-emergent activity was reported for 4i, 4j, 4k, 4L [a weed black mustard (Brassica nigra)], for 4k, 4L [weeds pale smartweed (Polygonum lapathifolium) and fathen (Chenopodium album)], as well as for 4k (weeds common poppy (Papaver rhoeas) and gallant soldier (Galinsoga parviflora)). The fungistatic activity of the Passerini adducts synthesized (4a–4L) was tested against six phytopathogenic fungi species (at 200 mg/L and procymidone as a control). The tested compounds showed a weak activity (% of inhibition) against: Alternaria alternata: 4g (47), 4i (26), 4j (26), 4k (50), Botrytis cinerea 4g (38), Fusarium culmorum 4g (44), Phytophthora cactorum 4i (35), 4j (35), 4k (30), Rhizoctonia solani 4g (30), 4i (24), Phytophthora infestans 4g (29), 4i (34), 4j (28), 4k (46).