2-Aryl-1,2,4-triazepin-3-ones

The synthesis and testing of heterocyclic compounds for herbicidal activity has been of continuous interest in our laboratories. As one phase of this program, a search of the literature indicated only a relatively few 2-aryl-l,2,4-triazin-3-ones (1, n-0) and 2-aryl-1,2,4-triazepin-3-ones (2) had been reported, and of those, none appeared to have been examined for herbicidal properties. A synthesis program was therefore initiated in order to access their potential as weed control agents. 

The silver acetate-promoted 1,3-dipolar cycloaddition of nitrilimines with 3(/f )-pheny]-4(A )-cinnamoyl-2-azetidinone produced the major adduct, 4-(4,5-dihydro- (g) pyrazol-5-yl)carbonyl-2-azetidinones, with high stereoselectivity.70 The 1,3-dipolar cycloadditions of substituted 2,7-dime(liyl-3-thioxo-3,4,5,6-ici.rahydro-2//- 1,2,41 triazepin-5-one with iV-aryl-C-ethoxycarbonylnitrilimines are highly chemoselective, where the sulfur atom of the dipolarophile interacts with the carbon atom of the dipole.71 The enantioselective 1,3-dipolar cycloaddition of nitrile imines with electron deficient acceptors produces dihydropyrazoles in the presence of 10 mol% of chiral Lewis acid catalyst.72... 

Aryl-l,2,4-triazin-3-ones and 2-Aryl-l,2,4-triazepin-3-ones... 

Aryl-l,2,4-triazepin-3-ones (2) were also prepared from the appropriate aryl isocyanate and 3-(methylamino)propionaldehyde diethyl acetal (Scheme 4). The yields in each reaction step were comparable to those for the synthesis of the triazin-3-ones. 

A new synthesis of 2-aryl-1,2,4-triazin-3-ones and 2-aryl-l,2,4-triazepin-3-ones from convenient starting materials has been demonstrated. Of these compounds, the triazin-3-ones were found to have herbicidal properties and with appropriate aromatic substituents, weed control can be obtained at low application rates. However, the weed control/crop tolerance ratio may limit the commercial application of the more active triazinones. 

M. Gupta, S. Paul, R. Gupta, Efficient and novel one-pot synthesis of antifungal active l-substituted-8-aryl-3-alkyl/aryl-4H-pyrazolo[4,5-f] [l,2,4]triazolo[4,3-b][l,2,4]triazepines using solid support, Eur. J. Med. Chem. 46 (2011) 631-635. 

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