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

Enantioselective dearomative cycloadditions of 4-nitroisoxazoleswith vinylethylene carbonate (2) proceeded in the presenceof Pd-2(dba)(3) and (S)-DTBM-SEGPHOSto give the corresponding bicyclic isoxazolines 3 and 4 in good to high yields with excellent enantioselectivities(& LE;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.

Automated summary

Enantioselective dearomative cycloadditions of 4-nitroisoxazoles with vinylethylene carbonate (2) in the presence of Pd-2(dba)(3) and (S)-DTBM-SEGPHOS afforded the corresponding bicyclic isoxazolines 3 and 4 in good to high yields with excellent enantioselectivities (& LE;99% ee). This method was also applicable to the reactions of N-tosyl vinyl aziridine and 2-methylidenetrimethylene carbonate. Further transformations of the resulting cycloadducts 4a and 4i led to the derivatives 10 and 11, as well as the novel tetracyclic skeleton 12.