Abstract
Dihydro-1,2,4-oxadiazoles were prepared using 1,3-dipolar cycloaddition of imines with nitrile oxides. Further reductive N-O bond cleavage furnished monosubstituted N-aryl amidines in good yield. Thus an efficient route for the synthesis of monosubstituted N-aryl amidines has been developed.
Highlights
N-Aryl amidines are important synthons for the synthesis of several heterocyclic compounds.[1]
1,3-Dipolar cycloaddition reactions have been used in our laboratory for the synthesis of various isoxazolidines[4] and 2-isoxazolines.[5]
Keeping above reported reactions in view, we envisaged that the N-O bond cleavage in 5aryl-4,5-dihydro-1,2,4-oxadiazoles might lead to the formation of either N(hydroxy(aryl)methyl)-N-arylbenzamides 27 produced by hydrolysis of a first-formed imine or N-aryl amidines (Scheme 1)
Summary
N-Aryl amidines are important synthons for the synthesis of several heterocyclic compounds.[1]. 1,3-Dipolar cycloaddition reactions have been used in our laboratory for the synthesis of various isoxazolidines[4] and 2-isoxazolines.[5] preparation of 5-aryl-4,5-dihydro-1,2,4oxadiazoles via 1,3-dipolar cycloaddition of nitrile oxides and imines has already been reported.[6] Bolton et al[7] reported a route to mono-substituted amidines via cleavage of N-O bond of 1,2,4oxadiazolin-5-ones under catalytic hydrogenation conditions.
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