Iron(III) Chloride/Diorganyl Diselenides: A Tool for Intramolecular Cyclization of Alkynone <i>O</i>-Methyloximes
作者:Adriane Sperança、Benhur Godoi、Gilson Zeni
DOI:10.1021/jo302770g
日期:2013.2.15
This report describes the synthesis of 4-organoselenylisoxazoles via FeCl3/RSeSeR-mediated intramolecular cyclization of allcynone O-methyloximes. The optimized conditions allowed the cyclization to proceed at room temperature under ambient atmosphere, and the reaction requires a short time to be completed. The reaction conditions tolerated neutral, electron-donating and electron-withdrawing groups present in both substrates, alkynone O-methyloximes and diorganyl diselenides. Treatment of 4-organoselenylisoxazoles with n-butyllithium, followed by trapping with electrophiles, furnished the functionalized isoxazoles in good yields. The obtained products also proved to be suitable substrates for the preparation of 4-bromoisoxazoles via Br/Se exchange reaction.
Isomerizable (E/Z)-alkynyl-O-methyl oximes employing TMSCl–NCS in chlorinative cyclization for the direct synthesis of 4-chloroisoxazoles
synthesized in moderate to excellent yields from (E/Z)-alkynyl-O-methyl oximes via chlorinative cyclization. The synthesis employs the combination of N-chlorosuccinimide (NCS) and chlorotrimethylsilane (TMSCl) in nitromethane solvent where chlorine (Cl2) and hydrochloric acid (HCl) are generated in situ. In addition, the current protocol is applicable to the synthesis of 4-bromo- and 4-iodoisoxazoles when