Aryl Radical Enabled, Copper-Catalyzed Sonogashira-Type Cross-Coupling of Alkynes with Alkyl Iodides

Despite the success of Sonogashira coupling for the synthesis of arylalkynes and conjugated enynes, the engagement of unactivated alkyl halides in such reactions remains historically challenging. We report herein a strategy that merges Cu-catalyzed alkyne transfer with the aryl radical activation of carbon-halide bonds to enable a general approach for the coupling of alkyl iodides with terminal alkynes. This unprecedented Sonogashira-type cross-coupling reaction tolerates a broad range of functional groups and has been applied to the late-stage cross-coupling of densely functionalized pharmaceutical agents as well as the synthesis of positron emission tomography tracers.

A General N-alkylation Platform via Copper Metallaphotoredox and Silyl Radical Activation of Alkyl Halides

The catalytic union of amides, sulfonamides, anilines, imines or N-heterocycles with a broad spectrum of electronically and sterically diverse alkyl bromides has been achieved via a visible light-induced metallaphotoredox platform. The use of a halogen abstraction-radical capture (HARC) mechanism allows for room temperature coupling of C(sp³ )-bromides using simple Cu(II) salts, effectively bypassing the prohibitively high barriers typically associated with thermally-induced S_N2 or S_N1 N-alkylation. This regio- and chemoselective protocol is compatible with >10 classes of medicinally-relevant N-nucleophiles, including established pharmaceutical agents, in addition to structurally diverse primary, secondary and tertiary alkyl bromides. Furthermore, the capacity of HARC methodologies to engage conventionally inert coupling partners is highlighted via the union of N-nucleophiles with cyclopropyl bromides and unactivated alkyl chlorides, substrates that are incompatible with nucleophilic substitution pathways. Preliminary mechanistic experiments validate the dual catalytic, open-shell nature of this platform, which enables reactivity previously unattainable in traditional halide-based N-alkylation systems.

Halide anions are formed from reactions between atomic metal anions and halogenated aromatic molecules

Atomic metal anions (AMAs) Fe^- , Cs^- , Cu^- and Ag^- were generated in the gas phase by collisionally decomposing the corresponding metal-oxalate anion. Mass selected AMAs were allowed to react with halogenated and nitrated molecules (C6H5Cl, C6H4Cl2, C6H3Cl3, C6H5I, C6H5Br and C6H5NO2) in the collision hexapole of a triple-quadrupole mass spectrometer. Observed reactions include the predominant formation of X^- (X = Cl, Br and I), as well as FeCl^- , FeCl2^- and FeCl3^- when Fe- reacted with the mono, di and tri-chlorobenzenes; reactions between 1,4-dichlorobenzene and Cs^- produced Cl^- , CsCl^- and CsCl2^- ; reactions involving iodobenzene also produced, CsI^- , CsI2^- and AgI^- . The results suggest that the reaction to form X^- (X = Cl, Br, I and NO2) may be a promising route to improving the detection efficiency by mass spectrometry for such analytes. Copyright © 2016 John Wiley & Sons, Ltd.