Synthesis and Herbicidal Activities of 4-Substituted 3-Aryl-5-tert-butyl-4-oxazolin-2-ones

A series of novel 3-aryl-5-tert-butyl-4-chloro-4-oxazolin-2-ones (16) have been prepared and found to show significant herbicidal activity in the grams per are range against broadleaf and narrowleaf weeds. The key step in the introduction of the chlorine atom at the 4-position of the 4-chloro-4-oxazolin-2-one ring is dichlorination using chlorine gas and subsequent dehydrochlorination using diazabicyclo[5.4.0]undecene. 4-Alkylthio- and 4-methyl-4-oxazolin-2-one rings were synthesized from α-substituted α-bromopinacolone by cyclization reaction. Among the synthesized compounds, 5-tert-butyl-4-chloro-3-[4-chloro-2-fluoro-5-(2-propynyloxy)phenyl]-4-oxazolin-2-one (16h) showed the greatest activity against several weeds without damage to transplanted rice in the paddy field. Keywords: 4-Oxazolin-2-one; α-bromoketone; cyclization; herbicide; biological isostere