Dioxygen-promoted regioselective oxidative heck arylations of electron-rich olefins with arylboronic acids.
Arylations of electron-rich heteroatom-substituted olefins were performed with arylboronic acids. This appears to constitute the first example of palladium(II)-catalyzed internal Heck arylations. The novel protocol exploits oxygen gas for environmentally benign reoxidation and a stable 1,10-phenanthroline bidentate ligand to promote the palladium(II) regeneration and to control the regioselectivity. Internal arylation is strongly favored with electron-rich arylboronic acids. DFT calculations support a charge-driven selectivity rationale, where phenyls substituted with electron-donating groups prefer the electron-poor alpha-carbon of the olefin. Experiments, verified by calculations, confirm the cationic nature of the catalytic route. This Heck methodology provides a facile and mild access to functionalized enamides. Controlled microwave heating and increased oxygen pressure were used to further reduce the reaction time to 1 h.
Andappan
Murugaiah M S
MM
Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, BMC, Uppsala University, Box-574, SE-751 23 Uppsala, Sweden.
Nilsson
Peter
P
von Schenck
Henrik
H
Larhed
Mats
M