Oxo-Rhenium-Catalyzed Radical Addition of Benzylic Alcohols to Olefins

Abstract

Although carbon radicals generated from a variety of alcohol derivatives have proven valuable in coupling and addition reactions, the direct use of alcohols as synthetically useful radical sources is less known. In this report, benzylic alcohols are shown to be effective radical precursors for addition reactions to alkenes when treated with triphenylphosphine or piperidine with the catalyst ReIO 2 (PPh 3 ) 2 (I).

Ring-closing C–O/C–O metathesis of ethers with primary aliphatic alcohols

“…4e), except for TEMPO, the basicity of which is known to be incompatible with Re 2 O 7 . No trapped radicals could be detected for all trapping agents tested, ruling out the possibility of a radical pathway 47 . Collectively, these results are best explained by hydroxy group activation pathway via perrhenate formation for the ring-closing C-O/C-O σ-bond metathesis (Fig.…”

Reactivity of metal dioxo complexes

“…In an analogous fashion, alkenes function as competent coupling partners for aryl radical homolyzed by reduced rhenium alkoxides. 132…”

“…In an analogous fashion, alkenes function as competent coupling partners for aryl radical homolyzed by reduced rhenium alkoxides. 132 Catalytic hydrosilation of carbon dioxide was catalyzed by a PNN-bound rhenium dioxo complex under high pressures at room temperature. 133 Initial addition of the silane generates a purported rhenium hydride siloxide followed by CO 2 insertion into the hydride generating bound formate.…”

“…135,136 MTO catalyzed deoxygenation reactions of biomass and biomasssurrogate molecules are extremely important, especially in the work of Toste, 137,138 Nicholas 139 and others and has been extensively reviewed elsewhere. [140][141][142][143][144][145] One specific instance where MDO's reactivity has been implicated is in the cleavage of lignin model compounds. MTO is converted to the active catalyst MDO in situ via hydrogen transfer and is active for the cleavage of the β-O-4 linkages in the lignin model compounds.…”

Recent Progress on Transition-Metal-Mediated Reductive C(sp3)–O Bond Radical Addition and Coupling Reactions

“…In 2020, Nicholas developed a Re-catalyzed addition of alcohol-derived benzyl radicals to olefins in the presence of PPh 3 or piperidine (Scheme 9 ). 20 Electronically varied benzyl alcohols were tolerated in the reaction with 1,1-diphenylethylene, but electron-deficient alcohols reacted sluggishly. Various electron-deficient alkenes and norbornene (a strained alkene) reacted smoothly with benzyl alcohol to produce the desired products in moderate to good yields.…”