Synthesis of new aza-bicyclic 2-isoxazolines by 1,3-dipolar cycloaddition of endocyclic enecarbamates and enamides with nitrile oxides

Novel aza-bicyclic 2-isoxazolines, 4,5-dihydroisoxazole[5,4-b]pyrrolidines, and 4,5-dihydroisoxazole[5,4-b]piperidines were synthesized in a highly regioselective manner through a 1,3-dipolar cycloaddition reaction of 5- and 6-membered endocyclic enecarbamates and enamides with several nitrile oxides in good to excellent yields. Hydrogenolysis of 5- and 6-membered Cbz-cycloadducts led to secondary amines, which presented distinctive stabilities. 2-Isoxazoline bisamides were obtained in good yields through a N-benzoylation, followed by ammonolysis of the secondary amine, or directly from ammonolysis of the cycloadducts.

n = 1 or 2; R = Me, Bn; R1 = aryl, OEt, OBn; R2 = CO2Et, CONH2, aryl, 2-furfuryl.