Pd-Catalyzed Asymmetric Cross-Coupling of Allyl Carbonates and Allyl Boronates

Key words

palladium-catalyzed cross-coupling - allyl carbonates - chiral phosphine ligands - deuterium labeling

Significance

The authors describe here a high-yielding, highly regio- and enantioselective cross-coupling of allyl carbonates and allyl boro­nates. Remarkably, nearly identical results are obtained for regioisomers 1 and 2. Importantly, aromatic and aliphatic allyl carbonates are tolerated under the reaction conditions. Allyl-allyl coupling in high regio- and stereoselectivity is a long-standing challenge in organic synthesis and this method provides an excellent solution.

Comment

High regioselectivity for the branched product 3 rather than the linear product 4 is obtained by choosing bidentate ligands with small bite angles. Mechanistic studies including deuterium labeling and stereochemical analysis support a B-Pd transmetalation pathway to generate intermediate C, followed by 3,3′-elimination, rather than a backside outer-sphere attack (E).