Water-Assisted Nitrile Oxide Cycloadditions: Synthesis of Isoxazoles and Stereoselective Syntheses of Isoxazolines and 1,2,4-Oxadiazoles.

摘要: Conventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water-assisted generation of proceeds mild acidic conditions (pH 4-5). Cycloadditions with alkynes and alkenes easily occurred water without using catalysts, thus yielding isoxazoles isoxazolines, respectively, excellent stereoselectivity toward five- six-membered cyclic alkenes. A double stereoselective cycloaddition two units a oxide cyclohexene was also achieved, 1,2,4-oxadiazole derivatives having unique hybrid isoxazoline-oxadiazole skeleton. Enantiomerically pure isoxazolines were prepared monoterpenes ring strain. In one case, isoxazoline butterfly-like structure simply prepared, it might be used as ligand asymmetric catalysis.