5-Chloroisoxazoles: A Versatile Starting Material for the Preparation of Amides, Anhydrides, Esters, and Thioesters of 2H-Azirine-2-carboxylic Acids

Amides, anhydrides, esters, and thioesters of 2H-azirine-2-carboxylic acids were prepared by a rapid procedure at room temperature involving FeCl2-catalyzed isomerization of 5-chloroisoxazoles to 2H-azirine-2-carbonyl chlorides, followed by reaction with N-, O-, or S-nucleophiles mediated by an ortho-substituted pyridine. With readily available chloroisoxazoles and a nucleophile, 2-picoline can be used as an inexpensive base. When a high yield of the acylation product is important, the reagent 2-(trimethylsilyl)pyridine/ethyl chloroformate is more suitable for the acylation with 2H-azirine-2-carbonyl chlorides.