The asymmetric 1,3-dipolar cycloaddition of nitrones possessing electron withdrawing group to an achiral allyl alcohol 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.
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.
A highly diastereo- and enantioselective 1,3-dipolar cycloaddition of nitrones bearing an amide moiety to allyl alcohol has been realized by using a catalytic amount of diisopropyl (R,R)-tartrate as a chiral auxiliary. Addition of amine N-oxide such as pyridine N-oxide, was crucial to realize a reproducible excellent enantioselectivity up to 98% ee.
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