Single-Electron-Transfer Strategy for Reductive Radical Cyclization: Fe(CO)₅ and Phenanthroline System

Abstract

An electron-transfer strategy using low-valent iron pentacarbonyl [Fe(CO)] to generate radical species from alkyl iodides was achieved. A range of pyrrolidines, tetrahydrofurans, and carbocycles were synthesized via 5-exo cyclization reactions of alkyl radical intermediates generated by electron transfer from a system involving Fe(CO), 1,10-phenanthroline, and diisopropylamine. Moreover, tandem addition reactions with Michael acceptors were also explored. Photophysical and electrochemical studies support a mechanism that involves electron transfer from the low-valent Fe reductant to alkyl iodide.

A Free‐Radical Reduction and Cyclization of Alkyl Halides Mediated by FeCl2

“…Photoredox catalysis has been proposed as an alternative to address these concerns raised by tin reagents, however, it often requires the use of expensive catalysts and is mostly limited to alkyl iodides . Recently, there are developments based on iron catalysis appeared in the literature, a close look into these studies reveals the requirement of either Grignard (Scheme a) or NaBH 4 reagents for the activation of iron catalyst, otherwise stoichiometric Fe(0) was used . Fensterbank et al.…”

“…Kang et al. used stoichiometric Fe(CO) 5 for the reductive radical cyclization . A methodology that can utilize iron and avoid the use of harsh conditions or reagents is highly desirable.…”

Vitamin B12-Catalyzed Dicarbofunctionalization of Bromoalkenes Under Visible Light Irradiation

“…Similar synthesis of pyrrolidines was reported by Kang and co-workers who utilized the Fe(CO) 5 -phenanthroline system as a catalyst. 19 Two-component reductive dicarbofuctionalizaton of alkenes via radical cyclization is also possible with Ni catalysis. 20 In this line, we have also shown that vitamin B 12 catalysis enables dicarbofunctionalization of electron-deficient alkenes.…”

“…Product was obtained according to General Procedure A from S3 as white crystals; yield: 50 mg (64%); dr = 1:3 (I/II /trans-3,4-Dimethyl-1-tosylpyrrolidine (7d) 19 Product was obtained according to General Procedure A from S1 as a rigid colorless oil; yield: 25 mg (40%). NMR spectra are consistent with the reported data.…”

Iron‐Promoted Radical Reactions: Current Status and Perspectives

“…An electron-transfer strategy by using the low-valent iron pentacarbonyl (3)t ogenerater adical species from alkyl iodides was recently described. [14] The reactionw as used to prepare ar ange of pyrrolidines, tetrahydrofurans, and carbocycles (5) through a5 -exo cyclization reaction of alkyl radicali ntermediates (Scheme 2).…”