Synthesis of Chiral N-Heterocyclic Allylboronates via the Enantioselective Borylative Dearomatization of Pyrroles

The first enantioselective synthesis of five-membered N-heterocyclic allylboronates has been accomplished by a C-B bond-forming dearomatization of pyrroles using a copper(I) catalyst. This reaction involves the regio- and enantioselective addition of a borylcopper(I) species to pyrrole-2-carboxylates, followed by the diastereoselective protonation of the resulting copper(I) enolate to afford pyrrolidine-type allylboronates. The products are highly attractive reagents for the rapid construction of pyrrolidine derivatives that bear five consecutive stereocenters via subsequent allylboration/oxidation processes.