Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C2-Symmetrical 1,5-Dienes

Transition-metal-catalyzed reductive coupling reactions have emerged as powerful protocols to construct C-C bonds. However, the development of enantioselective C(sp(3))-C(sp(3)) reductive coupling remains challenging. Herein, we report a highly regio-, diastereo-, and enantioselective reductive homocoupling of allylic acetates through cooperative palladium and photoredox catalysis using diisopropylethylamine or Hantzsch ester as a homogeneous organic reductant. This straightforward protocol enables the stereoselective construction of C(sp(3))-C(sp(3)) bonds under mild reaction conditions. A series of C-2-symmetrical chiral 1,5-dienes were easily prepared with excellent enantioselectivities (up to >99% ee), diastereoselectivities (up to >95:5 dr), and regioselectivities (up to >95:5 rr). The resultant chiral 1,5-dienes can be directly used as chiral ligands in asymmetric synthesis, and they can be also transformed into other valuable chiral ligands.

Automated summary

A highly regio-, diastereo-, and enantioselective reductive homocoupling of allylic acetates has been demonstrated using cooperative palladium and photoredox catalysis, providing a straightforward protocol for the stereoselective construction of C(sp(3))-C(sp(3)) bonds. This method enables the synthesis of a series of C-2-symmetrical chiral 1,5-dienes with excellent enantioselectivities, diastereoselectivities, and regioselectivities, which can be used as chiral ligands in asymmetric synthesis and transformed into other valuable chiral ligands.