Metal-Free Reductive Cleavage of C−O σ-bonds in Acyloin Derivatives by an Organic Neutral Super-Electron-Donor

Abstract

Neutral organic electron-donor 7, formally a pyridinylidene carbene dimer, effects reductive cleavage of C-O sigma-bonds in acyloin derivatives Ar(CO)CRR'OX (X = OAc, OPiv, OBz, OMs) and this represents the first cleavage of C-O sigma-bonds by a neutral organic electron-donor. The methodology is applicable to a large array of substrates and the reduced counterparts were isolated in good to excellent yields. For certain substrates, donor 7 behaves as a base, effecting condensation reactions with some acetate ester derivatives of acyloins, leading to butenolides. The variation in reactivity among the different substrates was rationalized.

Metal‐Free Reductive Cleavage of CN and SN Bonds by Photoactivated Electron Transfer from a Neutral Organic Donor

“…The donor 1 was the first neutral organic compound to reductively cleave aryl iodides to aryl radicals,1a while the stronger donors 2 1b and 3 1d converted aryl iodides into aryl anions. The compounds 2 and 3 also reduced Weinreb amides,1f acyloin derivatives,1h and some sulfones 1c…”

Structure and reactivity in neutral organic electron donors derived from 4-dimethylaminopyridine

“…Whatever about the standard potentials, in practice, the formation of aryl anions is only observed when the electron donor has E 1/2 = −1 V or is more negative [40]. In line with this, both the imidazole-derived donor 7 ( E 1/2 = −1.20 V vs SCE in DMF) [22–25] and the 4-dimethylaminopyridine (4-DMAP)-derived donor 8 [ E 1/2 (DMF) = −1.69 V vs Fc/Fc + ] [26–29], which would equate to −1.24 V vs SCE [ E (DMF) Fc/Fc+ = 0.45 V vs SCE] [41] react with aryl iodides to afford aryl anions. As an indication of their enhanced donor properties, these two donors can also cleave appropriate arenesulfonamides [25], aryl alkyl sulfones [25–26], Weinreb amides [28] and acyloin derivatives [29].…”

Hypervalent Iodine Mediated C–C Double Bond Activation: A Cascade Access to α-Keto Diacetates from Readily Available Cinnamic Acids

“…Other additives (CSA, TfOH, AcOH, TMSOTf and Ac 2 O) were also examined; unfortunately, no yield improvement was observed ( Table 1, entries 9-13). Combined additives were also evaluated; however, the yield was not improved when boron trifluoride-diethyl ether complex, acetic acid or acetic anhydride was coapplied with sulfuric acid, although the reaction time could be shortened ( Table 1, entries [14][15][16].…”