Electron-Transfer Reactions of Aromatic α,β-Epoxy Ketones:  Factors That Govern Selective Conversion to β-Diketones and β-Hydroxy Ketones

Abstract

Photoreaction of trans-1-(4-cyanophenyl)-3-phenyl-2,3-epoxy-1-propanone (trans-4'-cyanochalcone epoxide) with various electron donors was studied. Irradiation of this epoxy ketone with amines produced 1-(4-cyanophenyl)-3-phenyl-1,3-propanedione and 1-(4-cyanophenyl)-3-hydroxy-3-phenyl-1-propanone in various ratios depending on the kinds of amine and solvent used. A reaction mechanism involving an amine cation radical-assisted rearrangement of the epoxy ketone anion radical was proposed to be most consistent with the marked change in the yield of beta-diketone. On the other hand, the timing of proton transfer to the anionic intermediates is considered to be a key factor to yield the beta-hydroxy ketone. Information obtained from the photochemical study was useful to find the reaction conditions for the conversion of several aromatic epoxy ketones to hydroxy ketones by the use of samarium diiodide. Addition of methanol significantly changed the product distribution. Proper choice of water or methanol as a proton source produced hydroxy ketones in moderate to good yields.

1-(2-Furyl)-3-hydroxy-3-(4-phenylphenyl)prop-2-en-1-one

“…1,3-Diketones have been studied extensively in coordination chemistry (Ma et al, 1999;Yoshida et al, 2005). These compounds are often used as intermediates in syntheses (Hasegawa et al, 1997;Morris et al, 1996). 1,3-Diketones generally exist in enol and keto forms; the enol form is stabilized by the stronger intramolecular hydrogen bond (Vila et al, 1991).…”

3-(Biphenyl-1-yl)-1-(4-tert-butylphenyl)-3-hydroxyprop-2-en-1-one

“…For related literature, see: Bertolasi et al (1991); Gilli et al (2004); Gorczynski et al (2005); Hasegawa et al (1997); Liang et al (2003); Morris et al (1996); Vila et al (1991). independent and constrained refinement Á max = 0.15 e Å À3 Á min = À0.20 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).…”

Photochemical, Electrochemical and Enzymatic Methods for Ether‐Bond Cleavage

“…Scheme 5 shows that although the photolysis of ketooxirane 12 leads to 1,3-dioxolane 13 due to C-C bond cleavage, its irradiation in the presence of tributyltin hydride as the reducing agent gives β-hydroxy ketone 14 followed by C-O bond scission. [14,15] Wiest [16] has presented a contrary idea, i.e. oxirane formation by ring closure.…”