Water-Assisted Nitrile Oxide Cycloadditions: Synthesis of Isoxazoles and Stereoselective Syntheses of Isoxazolines and 1,2,4-Oxadiazoles.
Angew Chem Int Ed Engl
; 55(12): 3997-4001, 2016 Mar 14.
Article
em En
| MEDLINE
| ID: mdl-26914177
ABSTRACT
Conventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water-assisted generation of nitrile oxides proceeds under mild acidic conditions (pHâ
4-5). Cycloadditions of nitrile oxides with alkynes and alkenes easily occurred in water without using catalysts, thus yielding isoxazoles and isoxazolines, respectively, with excellent stereoselectivity toward five- and six-membered cyclic alkenes. A double stereoselective cycloaddition of two units of a nitrile oxide with cyclohexene was also achieved, thus yielding 1,2,4-oxadiazole derivatives having a unique hybrid isoxazoline-oxadiazole skeleton. Enantiomerically pure isoxazolines were prepared from monoterpenes with a ring strain. In one case, the isoxazoline with a butterfly-like structure was simply prepared, and it might be used as a ligand in asymmetric catalysis.
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MEDLINE
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En
Ano de publicação:
2016
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Article