Silicon-Based Lewis Acid Assisted Cinchona Alkaloid Catalysis: Highly Enantioselective Aza-Michael Reaction under Solvent-Free Conditions
摘要:
The study showed that a combination of an achiral silicon-based Lewis acid and chiral Lewis base, such as iodotrimethylsilane (TMSI) and cinchonine, generated a highly enantioselective catalyst system under solvent-free conditions which gave aromatic beta-amino ketones with up to >99% ee. Mechanistic studies demonstrate the enhanced asymmetric induction may be due to the combined and competitive activation of a carbonyl moiety of chalcone with cinchonine and the silicon-based Lewis acid in the aza-Michael reaction.
The first enantioselective Michael addition of aniline to chalcones was promoted by cheap and commercially available chincona alkaloids under solvent-free conditions. Variously substituted chalcones were examined as substrates giving the conjugate adducts in moderate to good enantioselectivity. The simple experimental procedure had no work-up and short reaction times, which are the notable advantages. (C) 2008 Elsevier Ltd. All rights reserved.
Brønsted acid catalyzed enantio- and diastereoselective one-pot three component Mannich reaction
A chiral derivative of 1,2-benzenedisulfonimide,(-)-4,5-dimethy1-3,6-bis(o-toly1)-1,2-benzenedisulfonimide is herein proven to be an efficient chiral catalyst in a one pot three-component Mannich protocol. Reaction conditions are mild and green, while the enantio- and diastereoselectivity are excellent. (C) 2015 Elsevier Ltd. All rights reserved.