MeZnO
MeZnOLeave this area blank for abstract info. Abstract-Asymmetric addition of diphenylzinc to C-alkynyl nitrones was achieved by utilizing di(t-butyl) (R,R)-tartrate as a chiral auxiliary to afford the corresponding optically active (S)-N-(1-phenyl-3-substituted prop-2-ynyl)hydroxylamines. By the addition of a product-like additive, enantiomeric enhancement was observed. A mixed zinc reagent, PhZnMe, improved enantioselection affording the hydroxylamines up to 92% ee.
* Graphical Abstract
The asymmetric 1,3-dipolar cycloaddition of nitrones possessing an electron-withdrawing group to allylic alcohols was achieved by the use of diisopropyl (R,R)-tartrate as a chiral auxiliary to afford the corresponding isoxazolidines with high regio-, diastereo-, and enantioselectivity. In the case of nitrones possessing an electron-withdrawing cyano or t-butoxycarbonyl group, 1,3-dipolar cycloaddition to 2-propen-1-ol occurred to produce the corresponding 3,5-trans-isoxazolidines with high enantioselectivity. To the contrary, nitrones possessing an amide moiety afforded the corresponding optically active 3,5-cis-isoxazolidines with completely opposite diastereoselectivity. A catalytic asymmetric 1,3-dipolar cycloaddition of nitrones possessing the N,N-diisopropylamide moiety to allylic alcohols was achieved to afford di- or trisubstituted isoxazolidines with excellent enantioselectivity of up to over 99% ee. The present asymmetric 1,3-dipolar cycloaddition was applied to the synthesis for the (2S,4R)-4-hydroxyornithine derivative.
Hydroxylamine derivatives Q 0110Asymmetric Addition of Phenylzinc Reagents to C-Alkynyl Nitrones. Enantiomeric Enhancement by a Product-Like Additive. -Chiral hydroxylamines (III) are formed by the addition of either diphenylzinc or phenyl(methyl)zinc to alkynyl nitrones in the presence of TAR as chiral auxiliary. Catalytic amounts of racemic product-like HYA enhance the enantioselectivity. In several cases, the application of PhZnMe gives higher enantioselectivities than ZnPh2. Catalytic amounts of HYA also significantly improve the enantioselectivity of the addition of ZnPh 2 to C-alkenyl nitrone (V). -(WEI, W.; HAMAMOTO, Y.; UKAJI*, Y.; INOMATA, K.; Tetrahedron: Asymmetry 19 (2008) 4, 476-481; Div. Mater. Sci., Grad. Sch. Nat. Sci. Technol., Kanazawa Univ., Kanazawa 920, Japan; Eng.) -Klein 37-065
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