Tetsuo Iwama

The Chalcogeno-Baylis-Hillman Reaction : A New Preparation of Allylic Alcohols from Aldehydes and Electron-deficient Alkenes.

Abstract The chalcogeno-Baylis-Hillman reaction catalyzed by sulfides and selenides, the group 16 element compounds, in the presence of Lewis acids was developed. The reactions proceeded smoothly by the use of 1 equiv of TiCl4 to give the coupling products in moderate to good yields. Bis-chalcogenides and related compounds were investigated as a catalyst, and 1,5-diselenocyclooctane gave the best result owing to stabilization of a cationic intermediate by the transannular interaction.

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.

Reactions of 1,2-thiazetidine 1,1-dioxides with organometallics: β-Elimination and NS bond cleavage

Abstract Reactions of 4-nonsubstituted β-sultams 1 with methyllithium gave only ( E )-vinylsulfonamides 2 , whereas 2-aminoethyl sulfones 3 were obtained as minor products by use of methylmagnesium bromide. Reactions of 4-monosubstituted β-sultams 6 with organolithiums gave ( E )-vinylsulfonamides 7 stereoselectively regardless of the configuration of 3- and 4-substituents. Treatment of 4,4-dimethyl-β-sultam 8a with methylmagnesium bromide and methyllithium provided 2-aminoethyl sulfone 9 and bis-sulfone 10 , respectively, and isopropyl phenyl sulfone 11 was obtained by use of phenyllithium or phenylmagnesium bromide.

Reactions of a β-sultam ring with Lewis acids via the CS bond cleavage

Abstract Selective CS bond cleavage of a β-sultam ring was achieved by the reactions with Lewis acids. Aryl ketones or aldehyde were provided from 3-aryl-β-sultams whereas β-sultams bearing a poorly migratory substituent at C-3 gave trans-1,2,3-oxathiazolidine 2-oxides and/or cis-aziridines. These reactions were influenced by the cation-stabilizing capability of C-4 substituents and by the configuration of the substituents at C-3 and C-4. Some 4-alkenyl-3-aryl-β-sultams underwent tandem intramolecular cyclization to give bicyclo[3.2.1]- and [2.2.1]-γ-sultams via the processes of CS bond cleavage, 1,2-aryl shift, cation-olefin cyclization and recombination of the sulfonyl anion.

Novel synthesis of medium-sized heterocycles containing a sulfur or selenium atom

Abstract Medium-sized sulfur- or selenium-containing heterocyclic compounds were synthesized by the reductive cross-piece bond cleavage of bicyclic sulfonium and selenonium salts bearing a bridgehead sulfur or selenium atom with magnesium metal or sodium borohydride.

Reduction of sulfonium and selenonium salts with samarium diiodide

Abstract Treatment of sulfonium and selenonium salts with 2 equiv of a THF solution of samarium diiodide caused the reductive cleavage of the C-S or C-Se bonds in high yields. The bond cleavage took place regioselectively between the positive sulfur or selenium atom and the carbon atom with an electron-withdrawing group or a vinyl group. Some medium-sized cyclic sulfides or selenides were synthesized by this method.

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.

Selective CN bond cleavage of 4-silyl-substituted 1,2-thiazetidine 1,1-dioxides with EtAlCl2: Stereospecific formation of (E)-vinylsulfonamides

Abstract Monosilylation of 1,2-thiazetidine 1,1-dioxides (β-sultams) furnished (3R ∗ , 4S ∗ )-4- silylated β-sultams stereoselectively. Treatment of 4-silylated β-sultams with a Lewis acid caused the selective CN bond cleavage because of the β-silyl stabilization against the resultant carbenium ion followed by desilylation to provide (E)-vinylsulfonamides stereospecifically.

Selective CS bond cleavage of 3-aryl-β-sultams with EtAlCl2

Abstract Selective CS bond cleavage of a β-sultam ring was achieved by the reactions of 3-aryl-β-sultams 1 with EtAlCl 2 . Aryl ketones 2 or aldehyde 3 were provided via processes of the CS bond cleavage, 1,2-aryl shift and imine formation. These reactions were influenced by the cation stabilizing capability of C-4 substituents and by the configuration of the substituents at C-3 and C-4.