Asymmetric hydrogenation of di and trisubstituted enol phosphinates with N,P-ligated iridium complexes.

The iridium-catalyzed asymmetric hydrogenation of various di- and trisubstituted enol phosphinates has been studied. Excellent enantioselectivities (up to >99% ee) and full conversion were observed for a range of substrates with both aromatic and aliphatic side chains. Enol phosphinates are structural analogues of enol acetates, and the hydrogenated alkyl phosphinate products can easily be transformed into the corresponding alcohols with conservation of stereochemistry. We have also hydrogenated, in excellent ee, several purely alkyl-substituted enol phosphinates, producing chiral alcohols that are difficult to obtain highly enantioselectively from ketone hydrogenations.