1,3-dimethyl-2-phenylbenzimidazoline (DMPBI)-acetic acid: An effective reagent system for photoinduced reductive transformation of alpha,beta-epoxy ketones to beta-hydroxy ketones

A combination of 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI) and acetic ac id has been utilized for photoinduced reductive transformation of alpha,bet a -epoxy ketones to beta -hydroxy ketones. Study, bn photoreactions using s everal proton donors revealed that acetic acid is superior to other proton donors such as HCl, p-TsOH, MeOH, and water. 1,3-Dimethyl-2-phenylbenzimida zolium was produced in the reaction with acetic acid while N-benzoyl-N,N'di methyl-o-phenylenediamine was formed in aqueous solvents. When THF solution s containing aryl carbonyl possessing alpha,beta -epoxy ketones and DMPBI a nd acetic acid were irradiated (lambda > 280 nm), beta -hydroxy ketones wer e isolated in good to excellent yields. photosensitized conditions (lambda > 340 nm) were employed for the reactions of alkyl carbonyl possessing alph a,beta -epoxy ketones.