A Pd(0)/blue light catalyzed carboiodination reaction is reported. A simple, air-stable catalytic system, utilizing [Pd(allyl)Cl] 2 and DPEPhos, generated a variety of iodinated hetero-and carbocycles including oxindoles, dihydrobenzofurans, indolines, a chromane, and a tetrahydronaphthalene. This protocol was tolerant of sensitive functional groups including free carboxylic acids, phenols, and anilines, as well as pyridines, while delivering products in up to 94% yield. Support for a reversible C−I bond formation via a single electron mechanism was obtained using a deuterium labeled substrate and a stoichiometric neopentylpalladium species.T ransition-metal catalyzed halogenation protocols have often hinged on gaining a deeper understanding of the reversibility of carbon−halogen bond forming events. One powerful synthetic strategy that implements reversible C−X bond formation is the palladium-catalyzed carboiodination reaction, wherein halogenated heterocycles can be built from the intramolecular transfer of a C(sp 2 )−X group across a tethered π-system. 1−4 Traditionally, palladium catalyzed carboiodination reactions involve a 2-electron mechanistic cycle and are initiated by a ground-state Pd(0) catalyst undergoing an oxidative addition with an aryl halide. 1,2,4 Recently, the use of blue light in conjunction with palladium catalysis has offered a convenient route to access excited-state palladium species. 5−10 Unlike their thermal counterparts, photochemical reactions involving excited-state Pd(0) are typically thought to involve tandem palladium/radical intermediates. These reactions can mimic the reactivity of ground state palladium species, via a single electron mechanism in domino reactions. 6,8,10−13 Though the presence of radical intermediates has been well established, 5,6,14 a mechanism involving both discrete Pd(II) intermediates and alkyl radical/Pd(I) species has not been broadly explored.Thermally initiated carboiodination reactions typically employ a palladium catalyst bearing bulky electron-rich phosphines, or a nickel catalyst and a PPh 3 , P(OR) 3 or an N,N-ligand. 1,15−20 These reaction mechanism initiate via an oxidative addition to the C−I bond, followed by a migratory insertion across the π-system, and terminate with a ligandmediated 3-center 2-electron, 18 or an H-bonding initiated S N 2type reductive elimination. 21 The most successful conditions for the palladium carboiodination reactions utilize high temperatures and QPhos or t-Bu 3 P, costly and air-sensitive bulky phosphines (Scheme 1a). Often times, bulky 3°-amine
A dual metal approach enables the use of unsymmetrical diallyl carbonates as viable enolate precursors for allylic alkylation reactions, allowing facile access to various α-quaternary allylated aldehydes and ketones. This methodology features a regioselective Pd-catalyzed decarboxylative oxidative addition, forming an electrophilic Pd π-allyl species and releasing an allylic alkoxide, which undergoes a Rh-catalyzed isomerization to an enolate in situ. Recombination of the Pd π-allyl species and Rhenolate nucleophile then affords the α-quaternary carbonyl compound.
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