Chemoselective Transfer Hydrogenation of Enamides Using Ru Pincer Complexes for the Synthesis of α-Amino Acids.

The chemoselective reduction of enamides to α-amino acids with iPrOH and EtOH as H-donors and solvents catalyzed by Ru pincer complexes is demonstrated. A range of α-amino acids is synthesized in good to excellent yields. Applications, large scale, and a one-pot experiment are also reported. Finally, deuterium-labeling experiments show high regioselectivity between the α- and ß-positions of the alkene unit.

Combined Role of the Asymmetric Counteranion-Directed Catalysis (ACDC) and Ionic Liquid Effect for the Enantioselective Biginelli Multicomponent Reaction.

This work describes new chiral task-specific ionic liquids bearing chiral anions as the catalysts for the enantioselective multicomponent Biginelli reaction. For the first time, the combined role of asymmetric counteranion-directed catalysis (ACDC) and ionic liquid effect (ILE) for the chiral induction in the Biginelli multicomponent reaction is demonstrated. The chiral induction arises from a supramolecular aggregate where the anion and the cation of the catalyst are alongside with a key cationic intermediate of the reaction. Each component of the new catalyst had a vital role for the chiral induction success. The mechanism of an asymmetric version of this multicomponent reaction is in addition demonstrated for the first time using electrospray (tandem) mass spectrometry, ESI-MS(/MS). The analyses indicated the reaction takes place preferentially and exclusively through the iminium mechanism. Unprecedented supramolecular aggregates were detected by ESI-MS and characterized by ESI-MS/MS. No intermediate of the other two possible reactions pathways could be detected. Theoretical calculations shed light on the transition state of the transformation during the key step of the chiral induction and helped to elucidate the roles of the chiral anion (ACDC contribution) and of the imidazolium-containing nonchiral cation derivative (ILE contribution) in the molecular reaction process.

Chemoselective Reduction of Azlactones Using Schwartz's Reagent.

Highly chemoselective addition of Schwartz's reagent to widely available azlactones is described. This method allows the preparation of challenged functionalized α-amino aldehydes, in good to high isolated yields at room temperature, after only 2 min reaction. The presence of sensitive functionalities or electronic factors does not compromise the potential of the method. The use of an excess of the reducing reagent gave a very functionalized allylic alcohol derivative in 86% yield.

A Brønsted base-promoted diastereoselective dimerization of azlactones.

A novel Brønsted base system for the diastereoselective dimerization of azlactones using trichloroacetate salts and acetonitrile has been developed. Desired products were obtained in good yields (60-93%) and with up to >19:1 dr after one hour of reaction. Additionally, the relative stereochemistry of the major dimer was assigned as being trans, by X-ray crystallographic analysis. The kinetic reaction profile was determined by using 1H NMR reaction monitoring and revealed a second order overall kinetic profile. Furthermore, by employing this methodology, a diastereoselective total synthesis of a functionalized analogue of streptopyrrolidine was accomplished in 65% overall yield.