Enantioselective allylation of aldehydes with allyltrichlorosilane promoted by new chiral organocatalysts

Enantioselective organic catalysis represents one of the more rapidly expanding fields of research in modern organic chemistry. A number of fundamental organic reaction that once required the use of metal-based, enantiopure catalyst can now be performed, with equal level of chemical and stereochemical efficiency, exploiting substoichiometric amounts of structurally simple organic molecules.1 In this context, "organic" hints to the metal-free nature of the catalyst, and emphasizes the advantages of performing a reaction under metal-free conditions. These advantages might include, inter alia, the possibility of: i) working in wet solvents and under an aerobic atmosphere; ii) dealing with a stable and robust catalyst; and iii) avoiding the problem of a (possibly) expensive and toxic metal leaching into the organic product.2 The catalytic enantioselective allylation of aldehydes provides a paradigmatic example of how an organometallic catalyst can be effectively replaced by a metal-free one.3 Once promoted by chiral Lewis acids, this reaction can currently be carried out in the presence of a variety of organic Lewis bases as catalysts, the most important being chiral pyridine N-oxides. On these bases we started a project aimed to the development of structurally simple chiral pyridine N-oxides as catalysts for the enantioselective allylation of aldehydes.