Direct C-H α-Arylation of Enones with Arl(O_2CR)_2 Reagents

摘要

α-Arylation of α,β-unsaturated ketones constitutes a powerful synthetic transformation. It is most commonly achieved via cross-coupling of α-haloenones, but this stepwise strategy requires prefunc-tionalized substrates and expensive catalysts. Direct enone C—H α-arylation would offer an atom- and step-economical alternative, but such reports are scarce. Herein we report the metal-free direct C—H arylation of enones mediated by hypervalent iodine reagents. The reaction proceeds via a reductive iodonium Claisen rearrangement of in situ-generated β-pyridinium silyl enol ethers. The aryl groups are derived from ArI(O_2CCF_3)_2 reagents, which are readily accessed from the parent iodoarenes. The reaction is tolerant of a wide range of substitution patterns, and the incorporated arenes maintain the valuable iodine functional handle. Mechanistic investigations implicate arylation via an umpoled "enolonium" species and show that the presence of a β-pyridinium moiety is critical for the desired C—C bond formation.