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

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, H-1 NMR, C-13 NMR, Se-77 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 cinerea4g (38), Fusarium culmorum4g (44), Phytophthora cactorum4i (35), 4j (35), 4k (30), Rhizoctonia solani4g (30), 4i (24), Phytophthora infestans4g (29), 4i (34), 4j (28), 4k (46). [GRAPHICS] .

Automated summary

A new method for modifying carboxylic groups in phenoxyacetic herbicides using the Passerini reaction has been proposed. The synthesized Passerini adducts showed excellent herbicidal and fungistatic activities with high yields.