Evidence for intermolecular hydrogen atom transfer in photostimulated SRN1 reactions involving ketone enolates

Abstract

dimethyl-3-pentanone with iodobenzene is accompanied by a competing reaction in which 2,4,4,6,8-pentamethylnonane-3,7-dione is formed by a mechanism originating with J-hydrogen abstraction from the enolate by phenyl radical.Sir: Photostimulated reactions of ketone enolates with carboaromatic and heteroaromatic halides have been shown to afford products resulting from introduction of an aryl or heteroaryl residue at the a carbon of the ketone.1-4 Considerable evidence1-5 has been gathered to show that these nucleophilic substitutions occur via a radical chain mechanism designated as SrnI6 and generalized in eq 1-4. Initiation (eq 1

Reactions of 1,3-Dihaloadamantanes with Carbanions in DMSO: Ring-Opening Reactions to Bicyclo[3.3.1]nonane Derivatives by the SRN1 Mechanism

“…It is known that when carbanions have hydrogens in the β-position, the reduction process competes with the coupling process . Carbanion 16 has two methyl groups in the β-position, which facilitates the reduction process.…”

Nucleophilic Substitution Reactions by Electron Transfer

“…173 Hydrogen atom abstraction from Nuhas been reported for the reaction of ArX with the enolates of tertiary esters 173 and of ketones, such as diisopropyl ketone. 174 Similarly, AdH (52%) is the main compound formed by reaction of the enolate ion of isobutyrophenone with 1-IAd. 175…”

Highly Active and Selective Catalysts for the Formation of α-Aryl Ketones

“…Selectivity is also a concern. While the preference for arylation at a methyl instead of a methine carbon (for ketones such as 3-methyl-2-butanone) is good (≥5:1), 9b, the selectivity for ketones that have both enolizable methylene and methyl carbons (such as 2-butanone) is significantly worse (1.3−3.2:1, in favor of substitution at the secondary carbon). 10a,d,f An additional problem is that hydrogens positioned β- to an enolate can be abstracted by aryl radicals, thus converting the aryl halide to the corresponding arene instead of the desired α-aryl ketone. 9b, …”