REDUCTION OF DELTA 2-ISOXAZOLINES. PART 3: RANEY-NICKEL CATALYZED FORMATION OF beta -HYDROXY KETONES.

Article abstract of DOI:10.1021/ja00356a021

The importance of the beta -hydroxy ketone moiety has led to the development of a wide variety of aldol type methodologies for its construction. A conceptually new approach to these 'aldol adducts' is presented on the basis of left bracket 3 plus 2 right bracket dipolar cycloaddition of in situ generated nitrile oxides and olefins followed by reduction of the resulting DELTA **2-isoxazolines. This approach provides a nice complement of the aldol type reaction. Optimum conditions for the transformation of DELTA **2-isoxazolines to beta -hydroxy ketones use Raney-nickel catalyst, boric acid, 5/1 MeOH/H//2O, and hydrogen gas. Under these mild conditions, 3-methyl-5-n-butyl- DELTA **2-isoxazoline is transformed to 4-hydroxy-2-octanone in high yield. Thus 'directed aldol' type adducts are readily available by selection of the appropriate olefin and nitrile oxide precursor (usually the 1 degree nitro compound).