Organocatalytic aza‐Michael/retro‐aza‐Michael reaction: Pronounced chirality amplification in aza‐Michael reaction and racemization via retro‐aza‐Michael reaction

AbstractA detailed experimental investigation of an aza‐Michael reaction of aniline and chalcone is presented. A series of Cinchona alkaloid‐derived organocatalysts with different functional groups were prepared and used in the aza‐Michael and retro‐aza‐Michael reaction. There was an interesting finding that a complete reversal of stereoselectivity when a benzoyl group was introduced to the cinchonine and cinchonidine. The chirality amplification vs. time proceeds in the quinine‐derived organocatalyst containing silicon‐based bulky group, QN‐TBS, ‐catalyzed aza‐Michael reaction under solvent‐free conditions. In addition, we have demonstrated for the first time that racemization was occurred in suitable solvents under mild conditions due to retro‐aza‐Michael reaction of the Michael adduct of aniline with chalcone. These indicate the equilibrium of retro‐aza‐Michael reaction and aza‐Michael reaction produce the happening of chirality amplification in aza‐Michael reaction and racemization via retro‐aza‐Michael reaction under different conditions, which would be beneficial to the development of novel chiral catalysts for the aza‐Michael reactions. Chirality, 2011. © 2011 Wiley‐Liss, Inc.