Redox-Neutral Coupling between Two C(sp3 )-H Bonds Enabled by 1,4-Palladium Shift for the Synthesis of Fused Heterocycles.

The intramolecular coupling of two C(sp3 )-H bonds to forge a C(sp3 )-C(sp3 ) bond is enabled by 1,4-Pd shift from a trisubstituted aryl bromide. Contrary to most C(sp3 )-C(sp3 ) cross-dehydrogenative couplings, this reaction operates under redox-neutral conditions, with the C-Br bond acting as an internal oxidant. Furthermore, it allows the coupling between two moderately acidic primary or secondary C-H bonds, which are adjacent to an oxygen or nitrogen atom on one side, and benzylic or adjacent to a carbonyl group on the other side. A variety of valuable fused heterocycles were obtained from easily accessible ortho-bromophenol and aniline precursors. The second C-H bond cleavage was successfully replaced with carbonyl insertion to generate other types of C(sp3 )-C(sp3 ) bonds.