Readily available carbohydrate-derived imines and amides as chiral ligands for asymmetric catalysis

An easy and diastereoseletive strategy for the synthesis of a new tetrahydrofuranic chiral aldehyde and a new tetrahydrofuranic acid derived from d-ribose is reported. These compounds have been shown to be useful starting materials for obtaining a never described before class of iminic- and amidic-carbohydrate-based chiral ligands, endowed with stability to purification on silica flash column and to storage, and characterised by the presence of a stereogenic centre α to the iminic or amidic bond. The first results obtained from the application of these chiral ligands in a model reaction, conjugate addition of Et2Zn to cyclohexenone, are discussed.