Organocatalytic Michael addition to (D)-mannitol-derived enantiopure nitroalkenes: A valuable strategy for the synthesis of densely functionalized chiral molecules

Carbohydrates are abundant renewable resources and are a feedstock for green chemistry and sustainable synthesis of the future. Among the hexoses and the pentoses present in biomass, mannitol was selected in the present project as a valuable platform, directly available from the chiral pool, to build highly functionalized molecules. Starting from (R)-2,3-O-cyclohexylidene glyceraldehyde, which is easily prepared in a large scale from D-mannitol, an enantiopure chiral nitro alkene was prepared by reaction with nitromethane, and its reactivity studied. Organocatalytic Michael addition of dimethyl malonate, β-keto esters, and other nucleophiles on the nitro alkene afforded high stereoselectivity and densely functionalized chiral molecules, which were further synthetically developed, leading to five-membered lactones and bicyclic lactams. Preliminary studies showed that the metal-free catalytic reaction on the chiral nitro alkene can be performed under continuous flow conditions, thus enabling the use of (micro)mesofluidic systems for the preparation of enantiomerically pure organic molecules from the chiral pool.