Electrochemically Tuned Oxidative [4+2] Annulation and Dioxygenation of Olefins with Hydroxamic Acids

Abstract

This work represents the first [4+2] annulation of hydroxamic acids with olefins for the synthesis of benzo[c][1,2]oxazines scaffold via anode‐selective electrochemical oxidation. This protocol features mild conditions, is oxidant free, shows high regioselectivity and stereoselectivity, broad substrate scope of both alkenes and hydroxamic acids, and is compatible with terpenes, peptides, and steroids. Significantly, the dioxygenation of olefins employing hydroxamic acid is also successfully achieved by switching the anode material under the same reaction conditions. The study not only reveals a new reactivity of hydroxamic acids and its first application in electrosynthesis but also provides a successful example of anode material‐tuned product selectivity.

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

“…In 2020, Han and co-workers hypothesized that a radical approach might provide access to benzo[1,2]oxazines by using an N -aryl hydroxamic acid as the 4π partner in reactions with olefin partners ( Scheme 206 ). 566 These researchers disclosed an electrochemical method for this benzoxazine synthesis. Optimal conditions were reported to consist of a solution of the hydroxamic acid and alkene substrates in a CH 2 Cl 2 /HFIP/MeCN (3.5:0.4:0.1) mixture with n -Bu 4 N + BF 4 – electrolyte.…”

“…The authors proposed sequential oxidation and deprotonation of the hydroxamic acid (e.g., for neutral N -phenyl- N -hydroxy ethyl carbamate, E 1/2 ox = +1.32 V vs Ag/Ag + in CH 2 Cl 2 /HFIP/MeCN (3.5:0.4:0.1)) 566 to generate an amidoxyl radical. Anti -Markovnikov addition of this intermediate to the olefin partner affords a C -centered radical species, which undergoes a second oxidation to the corresponding carbocation.…”

Radical 1,4/5‐Amino Shift Enables Access to Fluoroalkyl‐Containing Primary β(γ)‐Aminoketones under Metal‐Free Conditions

“…[11a] Unfortunately,t his model has not been promoted to apply to distal radical amino migration. Based on our persistent interest in radical-mediated organic synthesis, [12] we herein present an ovel radical 1,4/5-amino shift reaction. This migration employs alkene-tethered diphenyl ketoxime ethers as the easily obtainable substrates and is triggered by fluoroalkyl radical [13] derived from the electron donor-Scheme 1.…”

The Renaissance of Electro‐Organic Synthesis for the Difunctionalization of Alkenes and Alkynes: A Sustainable Approach

“…The electro-organic synthesis involving difunctionalization employing radical and ions can be carried out in mild conditions. The desired product in moderate to good yields can be obtained by the fine tuning of the cell potential or current and [126] 6 mA…”

“…The electrochemical transformation is carried out in an undivided cell equipped with RVC anode, platinum cathode employing tetrabutylammonium tetrafluoroborate in solvent mixture of dichloromethane/hexafluoroisopropanol/acetonitrile (Scheme 67). [126] The synthetic methodology was applied in synthesizing variety of biologically important precursors. The reaction proceeds via amidoxyl radical generated through anodic oxidation of hydroxamic acid.…”