Diamine-catalyzed asymmetric Michael additions of aldehydes and ketones to nitrostyrene

Highly efficient asymmetric organocatalytic Friedel-Crafts alkylation of indoles with alpha,beta-unsaturated aldehydes

The development of an improved organocatalyst, N-isopropylated bipyrrolidine 2a, for the asymmetric Friedel-Crafts alkylation of indoles with alpha,beta-unsaturated aldehydes has been presented. The new organocatalyst readily facilitates the enantioselective alkylation reaction, providing 3-alkylated indoles in good to high yields (62-89%) with high levels of enantioselectivity (80-93% ee) using only 2 mol% of catalyst loading.

One-pot synthesis of polycyclic nucleosides with unusual molecular skeletons

An alpha hydroxy pyrrolidine tricyclic nucleoside 3 and its spontaneous reaction with acetone is described. In this transformation highly functionalized polycyclic nucleosides with rather unusual molecular skeletons are formed in a complete regio- and stereoselective way. The reaction involves the formation of three new bonds, two of them novel carbon-carbon bonds, in a one-pot way. An enamine-iminium mechanism with participation of carbinolamine, iminium ion, and enamine intermediates is proposed as a plausible explanation for this transformation. The scope of the reaction is briefly studied concluding that the nature of the ketone (R(1)COR(2)) is critical for the initial attack of the NH to the carbonyl group.

Stereospecific synthesis of conformationally constrained gamma-amino acids: new foldamer building blocks that support helical secondary structure

A highly stereoselective synthesis of novel cyclically constrained gamma-amino acid residues is presented. The key step involves organocatalytic Michael addition of an aldehyde to 1-nitrocyclohexene. After aldehyde reduction, this approach provides optically active beta-substituted delta-nitro alcohols (96-99% ee), which can be converted to gamma-amino acid residues with a variety of substituents at the alpha position. We have used these new building blocks to prepare alpha/gamma-peptide foldamers that adopt a specific helical conformation in solution and in the solid state.