Phosphine Catalyzed Michael-Type Additions: The Synthesis of Glutamic Acid Derivatives from Arylidene-α-amino Esters.

The reaction of arylidene-α-amino esters with electrophilic alkenes to yield Michael-type addition compounds is optimized using several phosphines as organocatalysts. The transformation is very complicated due to the generation of several final compounds, including those derived from the 1,3-dipolar cycloadditions. For this reason, the selection of the reaction conditions is a very complex task and the slow addition of the acrylic system is very important to complete the process. The study of the variation in the structural components of the starting imino ester is performed as well as the expansion of other electron-poor alkenes. The crude products have a purity higher than 90% in most cases without any purification. A plausible mechanism is detailed based on the bibliography and the experimental results. The synthesis of pyroglutamate entities, after the reduction of the imino group and cyclization, is performed in high yields. In addition, the hydrolysis of the imino group, under acidic media, represents a direct access to glutamate surrogates.

Sequential Metal-Free Thermal 1,3-Dipolar Cycloaddition of Unactivated Azomethine Ylides.

The thermal 1,3-dipolar cycloaddition of unactivated azomethine ylides derived from allylamine and aromatic or heteroaromatic aldehydes with maleimides and 1,1- and 1,2-bis(phenylsulfonyl)ethylene affords endo-2,5- trans cycloadducts in moderate to good yields. DFT calculations provide evidence that the diastereoselectivity observed depends on the isomerization between S- and W-ylides according to Curtin-Hammett's principle. DFT calculations also explain the different diastereomeric ratio observed for 2-pyridyl and 2-thienyl derivatives in which the isomerization is not possible due to the competitiveness between isomerization barrier and the rate-limiting step (ylide formation barrier). This methodology is applied to the diastereoselective synthesis of a tricyclic thrombin inhibitor.

Synthesis of Allylic Amines by Asymmetric Transfer Hydrogenation of α,ß-Unsaturated N-(tert-Butylsulfinyl)imines.

Primary allylic amines with enantiomeric excesses from 97 to >99% were prepared by asymmetric transfer hydrogenation of α,ß-unsaturated N-(tert-butylsulfinyl)ketimines followed by removal of the sulfinyl group. The effect caused by different substituents at the C═C bond and at the iminic carbon atom on the chemoselectivity of the reduction was studied. The desired enantiomer of the final allylic amine can be synthesized by choosing the sulfinyl group with the appropriate absolute configuration.