Current Organic Synthesis - Volume 5, Issue 2, 2008

In this part other procedures of glycosylation reactions by direct activation are presented. We will focus on the n-pentenyl glycoside, the O-alkylation and the trichloroacetimidate methods. The use of glycosyl phosphates and glycals in glycosidation reactions are also discussed. Updated examples of these glycosylation methodologies involving total synthesis of oligosaccharides and related compounds are considered.

The area of asymmetric epoxidation of α,β-unsaturated carbonyl compounds is extensively studied owing to the synthetic importance of enantiomerically enriched epoxides as building blocks and products of pharmaceutical interest. In this review a comprehensive overview of the advances on the enantioselective organocatalytic methodologies for the epoxidation of α,β-unsaturated carbonyl compounds is presented. Dealing with the use of small organic molecules as catalysts, enantioselective organocatalysis is a flourishing new field of asymmetric synthesis to be considered complementary and in some examples alternative to metal complexes/chiral ligands and enzymatic approaches. In this context, new methodologies of enantioselective epoxidation of α,β-unsaturated ketones and aldehydes have been recently elaborated. The noteworthy features of these protocols focus on straightforwardly available, low cost, easy to handle organic catalysts and operational simplicity.

Some promising chiral catalysts and their role in asymmetric catalysis are discussed. Special attention has been paid to identify potential chiral hydrogen bond donors for the preparation of asymmetric α-aminophosphonates from achiral imine and dialkyl phosphite. A background review along with our ongoing work and futuristic trend in this area are presented.

α-Unsubstituted β-hydroxy acids (3-hydroxycarboxylic acids) are constituents of various natural products with pharmacological and other technical properties of interest. They are also important intermediates in organic synthesis. This article reviews various possible routes for asymmetric synthesis of enantiopure or enantiomerically enriched α-unsubstituted β-hydroxy acids.

The contribution of modified cyclodextrins in aqueous biphasic rhodium-catalyzed hydroformylation of higher olefins is tackled, taking into account previous results and new experimental data. The role of the cyclodextrins is emphasized and discussed through the analysis of numerous parameters. Development outlooks are also presented.

The structures, biological properties, preparations and synthetic applications of norbornane/ene bicyclic and heteroatombridged β-amino acids are discussed. These compounds are rare and unique β-alanine derivatives which can be used as bifunctional synthons for the preparation of heterocycles. Through peptidation, they form oligopeptide-like molecules with special helical structures.