Eietsu Hasegawa

Reductive transformation of α,β-epoxy ketones and other compounds promoted through photoinduced electron transfer processes with 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI)

Abstract Photoreactions of epoxy ketones, aromatic ketones, haloketones, and aromatic halides with 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI) were studied. Photoinducedsingle-electron transfer from DMPBI to such substrates initiates the reactions, followed by radical rearrangement and reduction to finally give several reduced products in modest to good yields.

First example of samarium diiodide-promoted sequential cyclization and ring-expansion reactions of α-bromomethyl cyclic β-keto esters to homologated γ-keto esters

SmI2 reductions of some aromatic as well as aliphatic α-bromomethyl cyclic β-keto esters produced one-carbon homologated γ-keto esters in modest to good yields.

Benzimidazoline-Dimethoxypyrene. An Effective Promoter System for Photoinduced Electron Transfer Promoted Reductive Transformations of Organic Compounds

2-(p-Methoxyphenyl)-1,3-dimethylbenzimidazoline (ADMBI) and 2-(o-hydroxyphenyl)-1,3-dimethylbenzimidazoline (HPDMBI) are used as reducing reagents in 1,8-dimethoxypyrene (1,8-DMP) sensitized, photoinduced electron transfer (PET) reactions. This system was effectively used for PET induced, reductive transformations of various organic substrates, including α,β-epoxy ketones, the olefin tethered 2-bromomethyl-1-tetralone, and o-allyloxy-iodobenzene, as well as for the deprotection reactions of dodecyl-2-benzoylbenzoate and N-sulfonylindole. The results of studies show that 1,8-DMP is a more effective sensitizer than the previously used 9-methylcarbazole for deprotection of N-methyl-4-picolinium ester.

Photoinduced electron transfer reactions of α,β-epoxy ketones with 2-phenyl-N,N-dimethylbenzimidazoline (PDMBI): Significant water effect on the reaction pathway

Abstract Irradiation of aroyl substituted epoxy ketones with 2-phenyl-N,N-dimethylbenzimidazoline in aqueous tetrhhydrofuran or aqueous benzene produced the corresponding aldols in good to excellent yields. Changing the amount of water addedsignificantly influenced the product distribution.

Photosensitized oxygenation reactions of 1,3-dithianes through cooperative single electron transfer pathway and singlet oxygen pathway

Abstract Photosensitized oxygenation reactions of 2-( p -methylphenyl)-1,3-dithiane 1a , and 2,2-di-( p -methylphenyl)-1,3-dithiane 1b afforded carbony compounds, sulfoxides, and sulfones at the various ratios through cooperative single electron transfer (SET) pathway and singlet oxygen pathway.

Cyclization and ring-expansion processes involving samarium diiodide promoted reductive formation and subsequent oxidative ring opening of cyclopropanol derivatives.

Samarium diiodide promoted reaction of various alpha-bromomethyl cycloalkanones, followed by subsequent treatment with trimethylsilyl chloride, leads to the production of cyclopropyl silyl ethers embedded in bicyclo[m.1.0]alkane frameworks. Treatment of the ethers with oxidative electron-transfer reagents, such as Fe(III), Ce(IV), and Mn(III) salts, generates ring-expanded ketones that convert to cyclic conjugated enones in moderate to good yields. In addition, the reduction-oxidation reaction sequences can be successfully performed in one pot. The regioselectivities of cyclopropane ring opening in the bicyclic substrates depend on the oxidizing agents used. For example, reactions promoted by FeCl3 with pyridine lead to the expected ring-expansion process involving internal-bond cleavage of bicycloalkane and yielding cyclic enones as final products. In contrast, reactions with Ce(NH4)2(NO3)6 or Mn(OAc)3 as oxidizing agents proceed by way of external-bond cleavage to give alpha-iodomethyl cycloalkanones.

Photoinduced single electron transfer reactions of 1,3-dithianes and 1,3-dithiolanes sensitized by triphenylpyrylium salt in the presence of molecular oxygen

Abstract Triphenylpyrylium salt sensitized photoreactions of several dithianes and dithiolanes produced carbonyl compounds in good yields in the presence of molecular oxygen. Molecular oxygen trapping of carbon radical intermediates generated through selective CS bond cleavage of dithiane and dithiolane cation radicals is proposed.

Deprotection of 1,3-dithianes by antimony pentachloride via single electron transfer processes

Abstract A variety of 1,3-dithianes was converted to the corresponding carbonyl compounds in good yields when those substances were treated with antimony pentachloride in methylene chloride. Single electron transfer from dithianes to antimony pentachloride was proposed as an initiation step of the reaction.

Selective Cα-O bond cleavage of chalcone epoxides induced by pyrylium salt sensitized photoreactions and dark reactions with cerium(iv) salts

The Cβ-O bonds of chalcone epoxides (1a, 1b) were selectively cleaved by pyrylium salt sensitized photoreactions, affording β-ketoaldehydes (2a, 2b) in CH2Cl2 and MeOH-adducts (3a, 3b) in MeOH. Similarly. cerium(IV) salts catalyzed the MeOH-adduct formations of 1a and 1b in the dark. On the other hand, nitrate ester (4b) was obtained on treatment of 1b with a cerium(IV) salt in MeCN.

Free radical trapping of α-keto radicals derived from α,β-epoxy ketones via photoinduced single electron transfer process

Abstract Irradiation of aromatic α,β-epoxy ketones in the presence of allyltributyltin afforded α-allyl-β-hydroxy ketones by a single electron transfer mechanism.