Efficient synthesis of 3,5‐functionalized isoxazoles and isoxazolines <i>via</i> 1,3‐dipolar cycloaddition reactions of 1‐propargyl‐ and 1‐allylbenzotriazoles

Abstract

Abstract 3‐Aryl‐5‐(benzotriazol‐1‐ylmethyl)‐ 10a‐f and 3‐ p ‐methoxyphenyl‐5‐(α‐benzotriazol‐1‐yl‐α‐ethoxymethyl)‐isoxazole (13) were prepared in high yields by 1,3‐dipolar cycloadditions of 1‐propargyl‐benzotriazole (5) and (α‐ethoxypropargyl)benzotriazole (8), respectively, with nitrite oxides 3a‐f (prepared in situ from benzohydroximoyl chlorides 2a‐f). The benzotriazol‐1‐ylmethyl moiety was further elaborated by sequential lithiation and reaction with aldehydes, alkyl halides and Michael acceptors. Similar 1,3‐cycloadditions using 1‐allylbenzotriazole (6) and 1‐(α‐ethoxyallyl)benzotriazole (7) afforded 3,5‐substituted isoxazolines 11b, f and 12 in excellent yields.