Asymmetric 1,3-dipolar cycloadditions of nitrones and methacrolein catalyzed by chiral bis-titanium lewis acid: a dramatic effect of N-substituent on nitrone.

Highly stereoselective 1,3-dipolar cycloadditions of methacrolein and nitrones could be realized by the use of bis-titanium chiral Lewis acid catalyst. Key to the success is the introduction of bulky N-substituent on nitrone to attenuate the undesired Lewis acid-nitrone complexation.