Pd-Catalyzed Regiodivergent Arylation of Cyclic Allylboronates

Abstract

Two complementary regiodivergent Pd-catalyzed arylations of the lithium salts of 6-membered cyclic allylboronates are reported. The two systems provide access to products featuring a polysubstituted alkene and a boronic ester and are both compatible with a broad range of aryl bromides or heteroaryl bromides. When a (P,N) ligand is employed, a highly C1selective arylation is favored. With the use of a Buchwald-type monophosphine ligand, a highly C3-selective arylation is favored. DFT calculations served to establish that a solvated dimer of the substrate is involved rather than a monomeric allylboronate. For the C3-arylation pathway, regioselectivity is governed mostly by steric factors during binding of the substrate to the metal center. A Curtin-Hammett equilibrium is crucial in determining C1 selectivity for the second catalytic system. A pivotal isomerization between two η2 -alkene-Pd(II) intermediates precedes ring-opening transition states and irreversible reductive elimination.