Chiral copper(II) phosphate catalyzed enantioselective synthesis of isochromene derivatives by sequential intramolecular cyclization and asymmetric transfer hydrogenation of o-alkynylacetophenones

A good mix: The title reaction of o-alkynylacetophenones with the Hantzsch ester in the presence of a chiral copper/phosphate catalyst proceeds in good yields with excellent enantioselectivities. The key intermediate for enantiocontrol is the ion pair of the carbonyl ylide with a chiral phosphate anion, and this process provides straight forward access to highly enantioriched chiral isochromenes.