Recent Advances in Transition‐Metal‐Free Oxygenation of Alkene C=C Double Bonds for Carbonyl Generation

Abstract

Carbonyl-forming reactions are a class of fundamental transformations in organic chemistry. Guided by the current importance of environmentally benign metal-free catalysis and synthesis, herein we review recent advances in carbonyl-generation reactions based on alkene C=C double oxygenation as well as related cascade reactions in the synthesis of diverse organic products. The content of this focus review consists of two important but different reaction models: oxygenation based on full C=C double-bond cleavage and oxygenation based on partial C=C double-bond cleavage.

NHC‐Stabilised Acetylene—How Far Can the Analogy Be Pushed?

“…[20] Other reactions of alkenes with oxygen also give ketones, but in nearly all cases the oxygen is activated, either by using O 3 as the oxygen source, high intensity irradiation of O 2 ,c onversion of triplet O 2 into singlet O 2 or by the use of radicalt ransfer reagents. [21] In our case the reactiono f the dienei su ncatalysed and occurs at room temperature with atmospherict riplet oxygen, which is rare. [22] Performing the reaction in ad arkened environmentg ave the same result, indicating that ambient light does not contributet ot he reaction.…”

Branched C=C and C−N Bond Cleavage on Enaminones toward the Synthesis of 3‐Acyl Quinolines

“…[17] Althought he exact process is not yet clear,i ti sw ellk nown outcomet hat the C=C double bond could get oxygenated to afford the carbonyl intermediate 6 or equivalent species via the oxidative cleavage. [18] The intramolecular nucleophilic addition of the phenyl ring to the active carbonyl yields intermediate 7.Q uinoline product 3 would be generated by dehydration of 7.…”

Metal‐Free C=C Double Bond Cleavage on Enaminones for the Synthesis of α‐Ketoamides by Free‐Radical Aerobic Oxygenation

“…In previous work, Wan et al[13a] developed the method synthesizing α‐ketoamides by a copper‐catalyzed enaminone C=C double bond cleavage wherein water acts as the source of oxygen (Scheme A). Considering the current emphasis in developing metal‐free organic synthesis, especially the metal‐free C=C bond cleavage‐based synthesis, it is highly desired to discover alternative method for α‐ketoamide synthesis without employing metal reagent. Herein, we report a metal‐free protocol for the enaminone C=C double bond cleavage, leading to the synthesis of α‐ketoamides with broad scope (Scheme B).…”