Asymmetric Synthesis of Bicyclic Isoxazolines via Dearomative Cycloaddition of 4-Nitroisoxazoles with Zwitterionic π-Allyl Palladium Species.

Abstract

Enantioselective dearomative cycloadditions of 4-nitroisoxazoles with vinylethylene carbonate (2) proceeded in the presence of Pd2(dba)3 and (S)-DTBM-SEGPHOS to give the corresponding bicyclic isoxazolines 3 and 4 in good to high yields with excellent enantioselectivities (≤99% ee). This synthetic approach could be applied to N-tosyl vinyl aziridine and 2-methylidenetrimethylene carbonate. Further transformations of the resulting cycloadducts 4a and 4i yielded not only its derivatives 10 and 11 but also the novel tetracyclic skeleton 12.