Enantioselective Synthesis of Multisubstituted Allenes by Cooperative Cu/Pd-Catalyzed 1,4-Arylboration of 1,3-Enynes

Abstract

A cooperative Cu/Pd-catalyzed enantioselective synthesis of multisubstituted allenes is established. By employing chiral sulfoxide phosphine (SOP)/Cu and PdCl₂ (dppf) complexes as catalysts, the 1,4-arylboration of 1,3-enynes provides an efficient approach to trisubstituted chiral allenes with up to 92 % yield and 97:3 er. Furthermore, by using 2-substituted 1,3-enynes as substrates, the tetrasubstituted chiral allenes were successfully generated using this strategy. Finally, theoretical calculations indicate that the transmetallation of the allenylcopper species is the rate-limiting step of this transformation.

Keywords: allenes; copper; enantioselectivity; palladium; synthetic methods.