L-proline's Derivatives Catalyzed Asymmetric Michael Addition

Abstract:Organic catalysts without noble metals have played an important role in the development of the catalytic reaction, due to their moderate effect, cost efficiency, environment friendly and other advantages. Organocatalytic asymmetric reaction is an increasingly active area in oraganic sythesis.The Michael addition reaction is one of the most important carbon-carbon bond-forming reactions in organic synthesis. Asymmetric organocatalytic Michael addition has attracted intense interests in the recent few years due to its stability, cheapness and the generation of multiple chiral centers in a single step. Recently, quite a number of small chiral organic molecules have been developed as stereoselective catalysts for asymmetric Michael reactions. Proline has been gradually recognized as a simple, abundant and powerful chiral catalyst for many asymmetric reactions.In this context, Asymmetric Michael addition reaction is studied from two sides as following.(1) One of the four Merrifield resin-supported pyrrolidine-based chiral organocatalysts, through A3-coupling reaction linkage have been developed and found to be highly effective catalysts for the Michael addition reaction of ketones with nitrostyrenes. The reactions generated the corresponding products in good yields (up to 98 %), excellent enantioselectivies (up to 98 % ee) and high diastereoselectivities (up to 99:1 d.r.). In addition, the catalysts can be reused at least five times without a significant loss of catalytic activity and stereoselectivity.(2) A modular sugar-based pyrrolidine was prepared and was found to be a highly enantioselective and cooperative organocatalyst for asymmetric Michael addition of ketones to nitrostyrenes. In the presence of 10 mol% of the organocatalysts, a pyrrolidine unit anchored to a natural D-glucose backbone through click chemistry, the Michael additions of ketones to nitrostyrenes underwent smoothly to generate the corresponding adducts in good yields (up to 98 %), high enantioselectivities (up to >99 % ee) and excellent diastereoselectivities (up to >99:1 d.r.) under solvent-free reaction conditions. In contrast to the above catalysts, some natural amino acids catalyzed the Michael addition reactions in low yields and stereoselectivities, or the substrates are very limited.In addition, we made research on the study of Heck reaction in ionic liquids. A kind of amino-functionalized ionic liquids has been prepared and investigated as ligand and base for the Heck reactions between aryl iodides and bromides with olefins in the presence of a catalytic amount of Pd submicron powder in [Bmim]PF6. The reactions generated the corresponding products in excellent yields under mild reaction conditions. The generality of this catalytic system to the different substrates also gave the satisfactory results. The key feature of the reaction is that Pd species and ionic liquids were easily recovered and reused for six times with constant activity.