Formation of β-hydroxyketones from α,β-epoxyketones by photoinduced single electron transfer reactions

Regioselective Dye-Induced Photocleavage of Epoxides as an Alternative Mild Synthetic Route to a Targeted Alcohol Functionality

“…The proposed mechanism is similar to that proposed by Hasegawa et al [11] and Cossy et al [12] to explain the UV light-induced cleavage of epoxides. The initial step is the excitation of the photosensitizer (PS) in the presence of visible light.…”

“…[11] After prolonged irradiation of the solution resulted in decomposition of the products, irradiation had to be terminated at low conversions. In a similar way, Cossy et al conducted the photolysis of a series of a,b-epoxyketones in acetonitrile at 254 nm in the presence of triethylamine, [12] and similarly reported decomposition of the photocleavage products after a prolonged irradiation period. Epling and Wang [13] reported a photolytic method for the cleavage of epoxides, which took place under mild conditions, gave good yields and high regioselectivities.…”

Photochemistry in synthesis: Where, when, and why

“…However, the same process can be carried out under mild conditions provided that the reaction occurs via the excited state, much easier to reduce than the corresponding ground state. In fact, the excited state is reduced by weak electron donors, such as aliphatic amines [29] or benzimidazolines [30]. The EATOS analysis carried out on the thermal process with Ti III and on the hν/NEt 3 systems shows that the main contributions are essentially due to the reagents in the first method and to the solvent in the latter one; indeed, the indexes for the photoprocess are higher, but only because of the solvent (>95 %, see Fig.…”

1,3-Dimethyl-2-phenylbenzimidazoline (DMPBI)-Acetic Acid: An Effective Reagent System for Photoinduced Reductive Transformation of α,β-Epoxy Ketones to β-Hydroxy Ketones

“…4 About the same time, Cossy and co-workers reported photoreactions of several aliphatic as well as aromatic epoxy ketones with triethylamine. 5 In these experiments, while the yields of hydroxy ketones were modest, several problems were also encountered: other compounds such as b-diketones were the major products in some cases 4a and the reactions could not be completed since prolonged irradiation caused decomposition of bhydroxy ketones. 5 Our subsequent mechanistic study demonstrated that selectivity of the reaction pathway either to produce b-diketones or b-hydroxy ketones depends on the nature of the radical cations of amines used.…”

“…5 In these experiments, while the yields of hydroxy ketones were modest, several problems were also encountered: other compounds such as b-diketones were the major products in some cases 4a and the reactions could not be completed since prolonged irradiation caused decomposition of bhydroxy ketones. 5 Our subsequent mechanistic study demonstrated that selectivity of the reaction pathway either to produce b-diketones or b-hydroxy ketones depends on the nature of the radical cations of amines used. 6 Now, we report herein a method to achieve photoinduced transformation of a,b-epoxy ketones to b-hydroxy ketones by using a combination of 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI) 7 and acetic acid, which is superior to the previously reported DMPBI-based method.…”