Organocatalytic Enantioselective Michael Addition of Oxazolones to 2‐Enoylpyridine N‐Oxides for Assembling of Pyridine N‐Oxides Featuring Vicinal Oxygen‐Containing Tetrasubstituted Stereocenters

Abstract

The thiourea catalyzed enantioselective Michael addition of 5H-oxazol-4-ones to 2-enoylpyridine N-oxides is described. Under mild conditions, a series of optically active pyridine N-oxides inlaid with oxazolone motif were obtained in high yields (62-99%) with excellent stereoselectivities (84-> 99% ee and > 20:1 dr). Notably, the method offers a direct synthetic approach to enantioenriched pyridine N-oxides featured by vicinal oxygencontaining tetrasubstituted stereocenters.

Review on Asymmetric Catalysis Employing 5H‐Oxazol‐4‐Ones as α‐Hydroxy Carboxylic Acid Surrogates

“…(Scheme 14). The reaction proceeded smoothly at room temperature with 10 mol % of catalyst 30 , yielding the Michael adduct in good to excellent yields and stereoselectivities [40] . The reaction tolerated a variety of aryl‐substituted 2‐enoylpyridine N ‐oxides.…”

“…The reaction proceeded smoothly at room temperature with 10 mol % of catalyst 30, yielding the Michael adduct in good to excellent yields and stereoselectivities. [40] The reaction tolerated a variety of aryl-substituted 2-enoylpyridine N-oxides. No significant electronic as well as steric effects on reaction rate and enantioselectivity were observed.…”