Tuning the reactivity of alkoxyl radicals from 1,5-hydrogen atom transfer to 1,2-silyl transfer

Abstract

Controlling the reactivity of reactive intermediates is essential to achieve selective transformations. Due to the facile 1,5-hydrogen atom transfer (HAT), alkoxyl radicals have been proven to be important synthetic intermediates for the δ-functionalization of alcohols. Herein, we disclose a strategy to inhibit 1,5-HAT by introducing a silyl group into the α-position of alkoxyl radicals. The efficient radical 1,2-silyl transfer (SiT) allows us to make various α-functionalized products from alcohol substrates. Compared with the direct generation of α-carbon radicals from oxidation of α-C-H bond of alcohols, the 1,2-SiT strategy distinguishes itself by the generation of alkoxyl radicals, the tolerance of many functional groups, such as intramolecular hydroxyl groups and C-H bonds next to oxygen atoms, and the use of silyl alcohols as limiting reagents.

Tuning the Reactivity of Alkoxyl Radicals from Cyclization to 1,2-Silyl Transfer: Stereoselective Synthesis of β-Substituted Cycloalcohols

“…Recently, we reported that radical 1,2-silyl transfer (1,2-SiT) of alkoxyl radicals could be favored over 1,5-HAT and β-carbon elimination in some cases. , We wondered whether alkoxyl radicals A could still undergo 1,2-SiT to generate ketyl radicals B , instead of generating radicals C through intramolecular olefin addition (Scheme b). If this hypothesis works, the carbon radical B could add to the alkene to generate carbon radicals D or D′ .…”

Radical Transformation of Aliphatic C–H Bonds to Oxime Ethers via Hydrogen Atom Transfer

“…In addition, many oximes and oxime ethers show antifungal, antibacterial, or antitumor activity (Scheme B) . For these reasons, the development of efficient methods for the synthesis of oxime ethers has attracted considerable attention from chemists . Recently, the Kim group reported innovative work involving radical coupling reactions between sulfonyl-containing oxime ethers and alkyl halides to afford oxime ethers .…”

Cascade cyclization of alkene-tethered acylsilanes and allylic sulfones enabled by unproductive energy transfer photocatalysis

“…The generation of more stable secondary carbon radical 10a is favorable over primary carbon radical 10b . The intramolecular addition of 10a to the acylsilane would generate alkoxyl radical 11 , followed by radical Brook rearrangement to generate 12 66 – 76 . Giese-type addition of 12 to allylic sulfone would generate intermediate 13 , which would eliminate PhSO 2 radical and product 3a to close mechanism cycle.…”