Efficient synthesis of 3,5-functionalized isoxazoles and isoxazolines via 1,3-dipolar cycloaddition reactions of 1-propargyl- and 1-allylbenzotriazoles

3-Aryl-5-(benzotriazol-1-ylmethyl)- 10a-f and 3-p- methoxyphenyl-5-(alpha - benzotriazol-1-y1-alpha -ethoxymethyl)-isoxazole (13) were prepared in high yields by 1,3-dipolar cycloadditions of 1-propargylbenzotriazole (5) and ( alpha -ethoxypropargyl)benzotriazole (8), respectively, with nitrile oxides 3a-f (prepared in situ from benzohydroximoyl chlorides 2a-f). The benzotri azol-1-ylmethyl moiety was further elaborated by sequential lithiation and reaction with aldehydes, alkyl halides and Michael accepters. Similar 1,3-c ycloadditions using l-allylbenzotriazole (6) and 1-(alpha -ethoxyallyl)benz otriazole (7) afforded 3,5-substituted isoxazolines 11b,f and 12 in excelle nt yields.