Enantioselective 1,3‐dipolar cycloaddition reactions using complexes of (−)‐sparteine

Abstract

Sparteine Yb(OTf) 3 O N R CH 2 OH + O N CH 2 OH R 1 R ee up to 68% R 1Regio-and stereoselective 1,3-dipolar cycloaddition of nitrile oxides to internal 2-pentenols and ,unsaturated esters catalyzed by (-) sparteine-lanthanide complexes affords corresponding 3-aryl-2isoxazolines with enantioselectivities up to 68% ee.

Recent Advances of Catalytic Asymmetric 1,3-Dipolar Cycloadditions

“…As a related study, Yb(III)/(−)-sparteine complex-mediated 1,3-DC of nitrile oxide with allylic alcohol was later developed by another group. 206 The development of chiral Lewis acid-catalyzed 1,3-DC of nitrile oxides and electron-deficient alkenes is a challenging task because nitrile oxides coordinate strongly to Lewis acid, dimerize easily, and facilitate background reaction. In addition, the incompatibility of Lewis acid catalysis with the base required for the generation of nitrile oxides from hydroximoyl chlorides is problematic.…”

“…The addition of hydroximoyl chloride to the solution of a catalytic amount of diisopropyl ( R , R )-tartrate, Et 2 Zn, and allyl alcohol gave rise to the chiral isoxazoline 309 with good enantioselectivity. As a related study, Yb­(III)/(−)-sparteine complex-mediated 1,3-DC of nitrile oxide with allylic alcohol was later developed by another group …”

Recent Advances in Nitrile Oxide Cycloadditions. Synthesis of Isoxazolines

“…Alkyl as well as aryl nitrile oxides generated from the corresponding aldoximes were tolerated under these conditions, and gave excellent enantioselectivities and good yields (Scheme 8). Go biewski et al [26] recently reported an enantioselective nitrile oxide cycloaddition to Z-pent-2-en-1-ol 19 using a chiral Lewis acid. The authors used Yb(OTf) 3 as the Lewis acid and (-)-sparteine as the chiral ligand.…”

1,3‐Dipolar Cycloaddition Reaction of Nitrile Oxides Revisited—Unusual Side Products Characterized by 2D NMR

“…We carried out many cycloaddition reactions of 21 nitrile oxides to two unsaturated alcohols, 14 esters, and 12 amides mediated by complexes of lanthanides and other Lewis acids with chiral ligands obtaining products with variable regioselectivities and enantioselectivities up to 99%, including several biologically active carboxamides . Herein, we wish to present the results of a thorough analysis of the reaction mixtures that showed the presence of several side products, some of which were quite unexpected and interesting from the synthetic point of view.…”