Visible-Light-Induced Selective Photolysis of Phosphonium Iodide Salts for Monofluoromethylations.

The sigma (σ)-hole effect has emerged as a promising tool to construct novel architectures endowed with new properties. A simple yet effective strategy for the generation of monofluoromethyl radicals is a continuing challenge within the synthetic community. Fluoromethylphosphonium salts are easily available, air- and thermally stable, as well as simple-to-handle. Herein, we report the ability of the σ-hole effect to facilitate the visible-light-triggered photolysis of phosphonium iodide salts, a charge-transfer complex, selectively giving fluoromethyl radicals. The usefulness and versatility of this new protocol are demonstrated through the mono-, di-, and trifluoromethylation of a variety of alkenes.

DFT insight into asymmetric alkyl-alkyl bond formation via nickel-catalysed enantioconvergent reductive coupling of racemic electrophiles with olefins.

A DFT study has been conducted to understand the asymmetric alkyl-alkyl bond formation through nickel-catalysed reductive coupling of racemic alkyl bromide with olefin in the presence of hydrosilane and K3PO4. The key findings of the study include: (i) under the reductive experimental conditions, the Ni(ii) precursor is easily activated/reduced to Ni(0) species which can serve as an active species to start a Ni(0)/Ni(ii) catalytic cycle. (ii) Alternatively, the reaction may proceed via a Ni(i)/Ni(ii)/Ni(iii) catalytic cycle starting with a Ni(i) species such as Ni(i)-Br. The generation of a Ni(i) active species via comproportionation of Ni(ii) and Ni(0) species is highly unlikely, because the necessary Ni(0) species is strongly stabilized by olefin. Alternatively, a cage effect enabled generation of a Ni(i) active catalyst from the Ni(ii) species involved in the Ni(0)/Ni(ii) cycle was proposed to be a viable mechanism. (iii) In both catalytic cycles, K3PO4 greatly facilitates the hydrosilane hydride transfer for reducing olefin to an alkyl coupling partner. The reduction proceeds by converting a Ni-Br bond to a Ni-H bond via hydrosilane hydride transfer to a Ni-alkyl bond via olefin insertion. On the basis of two catalytic cycles, the origins for enantioconvergence and enantioselectivity control were discussed.

Photoinduced α-Alkenylation of Katritzky Salts: Synthesis of ß,γ-Unsaturated Esters.

ß,γ-Unsaturated esters are building blocks in biologically important compounds, pharmaceuticals, and natural products. Because the current synthetic methods often require transition-metal catalysts or lack general variants, we herein describe a simple NaI-involved photoinduced deaminative alkenylation for their synthesis in the absence of photocatalysts and additives. The density functional theory study unveils that the electrostatic interaction of NaI with Katritzky salts is the key to forming the photoactive electron donor-acceptor complex, thus leading to the alkyl radicals for the alkenylation.

Site-Selective Pyridyl Alkyl Ketone Synthesis from N-Alkenoxypyridiniums through Boekelheide-Type Rearrangements.

The Boekelheide rearrangement is often employed for the oxy-functionalization of alkyl groups in the 2-position of pyridines, yet the corresponding alkylation reaction has so far not been realized since 1954. N-Alkenoxypyridinium functionalization has been widely applied to synthesize various carbonyl compounds by only using the carbonyl unit. Herein, we describe a simple yet efficient alkylation of N-alkenoxypyridiniums through the Boekelheide reaction for the synthesis of ß-2-pyridyl alkyl ketones.