Asymmetric Oxidative Dimerization of the Enolates of N-[Bis(methylthio)methylene]- and N-(Diphenylmethylene)glycine Esters.

The oxidative dimerization of glycinates 1 with iodine takes place under kinetic control. The stereochemistry of the resulting 3-aminoaspartate 3 depends on the method used (base/solvent) to generate the corresponding enolate 2. Under suitable conditions, high yields and diastereomeric excesses in favor of the threo derivatives 3-I, which have C(2) symmetry, were obtained. In the presence of 8-phenylmenthol as chiral auxiliary (2S, 3S)-3-aminoaspartic acid 5-I was synthesized.

Diastereoselective Synthesis of alpha,alpha-Disubstituted gamma-Carboxypyroglutamates via Sm(III)-Azomethine Ylide Cycloadditions.

Sm(III)-azomethine ylides 2 have been generated from ketones 1. Cycloaddition of ylides 2 with alpha,beta-unsaturated esters 3 through a transition state chelation-controlled by the metal allowed for the asymmetric synthesis of gamma-carboxypyroglutamates having a quaternary alpha-carbon that are potentially useful in the synthesis of neuroprotective agents.