Hironori Kinoshita

Reexamination of Products and the Reaction Mechanism of the Chalcogeno-Baylis–Hillman Reaction: Chalcogenide–TiCl4-mediated Reactions of Electron-Deficient Alkenes with Aldehydes

Abstract Reactions of p -nitrobenzaldehyde ( 4 ) with methyl vinyl ketone ( 5 ) were conducted in the presence of TiCl 4 and dimethyl sulfide ( 3 ) or selenopyranone 6 . When the raw product was purified by column chromatography on silica gel, α-chloromethyl aldol 8 was obtained as a mixture of diastereoisomers 8a and 8b . In contrast, purification of the raw product by preparative TLC on silica gel gave α-methylene aldol 7 . The mechanism for the formation of α-chloromethyl aldol 8 and diasteroselection for the syn -isomer 8a and anti -isomer 8b are discussed.

2,6-Diphenyl-4H-chalcogenopyran-4-ones and 2,6-diphenyl-4H-chalcogenopyran-4-thiones: a new catalyst for the Baylis-Hillman reaction

Abstract 2,6-Diphenyl-4 H -chalcogenopyran-4-ones and 2,6-diphenyl-4 H -chalcogenopyran-4-thiones, a new series of catalysts for the Baylis-Hillman reaction, were investigated. The reactions proceeded smoothly in the presence of 1 mol eq. of TiCl 4 under atmospheric pressure at 0°C, giving adducts in moderate to high yields. Chalcogenopyranones and chalcogenopyranthiones were a more efficient kind of catalyst than Me 2 S.

Tandem Michael-aldol reaction via 6-endo-dig cyclization of ynone-chalcogenides: synthesis of 2-unsubstituted 3-(hydroxyalkyl)chalcogenochromen-4-ones

The reactions of 1-(2-methylchalcogenophenyl)propynone with aldehydes gave 3-(hydroxyalkyl)chalcogenochromen-4-ones via the 6-endo-dig cyclization and aldol reaction. Selenochromen-4-ones were obtained in higher yields than the thiochromen-4-ones.

Chalcogenide-TiCl4-mediated reactions of S-ethyl thioacrylate with aldehydes

Abstract The reaction of p -nitrobenzaldehyde ( 1a ) with S -ethyl thioacrylate ( 2 ) catalyzed by chalcogenide-TiCl 4 gave a mixture of Baylis–Hillman adduct 4a and syn - and anti -2-(chloromethyl)-3-hydroxy-3-( p -nitrophenyl)propanethioates 5a in the ratio of 4 : syn - 5 : anti - 5 =5:65:30. The crude product obtained from the reaction of p -trifluoromethyl derivative 1b with 2 was treated with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene to give 4 in 71% overall yield, while treatment of the crude product with Ti(O- i- Pr) 4 afforded isopropyl 2-(α-hydroxy- p -trifluoromethylbenzyl)acrylate 6 (49%), S -ethyl 2-(ethylthiomethyl)-3-hydroxy-3-( p -trifluoromethylphenyl)thiopropyonate 7 (2%) and S -ethyl 2-(chloromethyl)-3-( p -trifluoromethylphenyl)thioacrylate 8 (15%). Reactions of 2 with other various aldehydes followed by the treatment with DBU or Ti(O- i- Pr) 4 gave the thioacrylates 4 and isopropyl acrylates 6 , respectively, in fair to good yields. The formation mechanism for 2-(chloromethyl)propanethioate 5 is discussed.

The chalcogeno-Baylis–Hillman reaction of ketones and α-dicarbonyl compounds

1-[2-(Methylsulfanyl)phenyl]prop-2-en-1-one reacted with ketones, α-diketones, and α-keto esters in the presence of BF3·Et2O to give Morita–Baylis–Hillman adducts.

Chalcogeno-Morita-Baylis-Hillman Reaction of Chalcogenide-Enones with Carbonyl Compounds

Abstract The Chalcogeno-Morita-Baylis-Hillman reaction was achieved by the reactions of 2-(methylchalcogeno)phenyl vinyl ketones with carbonyl compounds or acetals in the presence of BF3· Et2O. This reaction proceeds via the intramolecular Michael addition of the chalcogenide group to an enone moiety followed by the aldol reaction of the resulting chalcogenonio-enolate with an aldehyde. The reactions were worked up with triethylamine or saturated aqueous NaHCO3 to give the α -methylene aldols (the Morita-Baylis-Hillman adducts).

Self-assisted tandem Michael-aldol reactions of α,β-unsaturated ketones with aldehydes

The tandem Michael-aldol reaction of 1-[2-(methylsulfanyl)phenyl]prop-2-en-1-one (1) or the seleno congener 4 with p-nitrobenzaldehyde in the presence of BF3·Et2O gave the Baylis–Hillman adduct 2 or 5 and onium salt 3 or 6, respectively, and selenochromanone 7 from 4.