A New Synthesis of α-Amino Acid Thioesters by Pummerer Reaction of 3-Substituted-4-sulfinyl-β-sultams

α-Amino acid thioesters were synthesized by the Pummerer reaction of 3-substituted-4-sulfinyl-β-sultams with TFAA. The 3-substituted-4-sulfinyl-β-sultams were prepared from the corresponding β-sultams by sulfenylation with diphenyl disulfide followed by m-CPBA oxidation. Diastereoselective synthesis of β-sultams by 1,3-asymmetric induction in [2 + 2] cycloaddition of a sulfene intermediate and chiral imines in solution-phase was studied, and it was found that N-alkylimines gave better diastereoselectivities than N-aralkylimines. The use of imines derived from (R)- and (S)-α-methylbenzylamine followed by separation of the major and minor diastereomers gave enantiopure 3-substituted-N-methylbenzyl-β-sultams. These β-sultams were then converted to N-methylbenzyl-α-amino acid thioesters via sulfenylation and Pummerer rearrangement with high or complete retention of configuration

A New Synthesis of α-Amino Acid Thioesters by Pummerer Reaction of 3-Substituted-4-sulfinyl-β-sultams

α-Amino acid thioesters were synthesized by the Pummerer reaction of 3-substituted-4-sulfinyl-β-sultams with TFAA. The 3-substituted-4-sulfinyl-β-sultams were prepared from the corresponding β-sultams by sulfenylation with diphenyl disulfide followed by m-CPBA oxidation. Diastereoselective synthesis of β-sultams by 1,3-asymmetric induction in [2 + 2] cycloaddition of a sulfene intermediate and chiral imines in solution-phase was studied, and it was found that N-alkylimines gave better diastereoselectivities than N-aralkylimines. The use of imines derived from (R)- and (S)-α-methylbenzylamine followed by separation of the major and minor diastereomers gave enantiopure 3-substituted-N-methylbenzyl-β-sultams. These β-sultams were then converted to N-methylbenzyl-α-amino acid thioesters via sulfenylation and Pummerer rearrangement with high or complete retention of configuration

Development of Novel Diastereoselective Alkenylation of Enolates Using Alkenylselenonium Salts

A novel alkenylation of enolates using alkenylselenonium salts is described. A reaction of lithium enolates, which were prepared in situ by the reaction of LiHMDS and carbonyl compounds, with alkenylselenonium salts gave the ethenylation products of carbonyl compounds in high yield. Diastereoselective alkenylation was also accomplished by the reaction of the enolates derived from N-acyl-1,3-oxazolidin-2-ones with the alkenylselenonium salt to afford good results (up to 92% yield and up to 95% de)

Development of Novel Diastereoselective Alkenylation of Enolates Using Alkenylselenonium Salts

A novel alkenylation of enolates using alkenylselenonium salts is described. A reaction of lithium enolates, which were prepared in situ by the reaction of LiHMDS and carbonyl compounds, with alkenylselenonium salts gave the ethenylation products of carbonyl compounds in high yield. Diastereoselective alkenylation was also accomplished by the reaction of the enolates derived from N-acyl-1,3-oxazolidin-2-ones with the alkenylselenonium salt to afford good results (up to 92% yield and up to 95% de)

Stereospecific Syntheses of 5-Alkyl-3-ethoxy-2-((phenylchalcogeno)methylene)tetrahydrofurans

2-Ethoxy-4-(phenylchalcogeno)but-3-ynyl ketones 1−10 were reduced with LiBH4 in Et2O diastereoselectively to give 5-(phenylchalcogeno)pent-4-yn-1-ols 11−20. Treatment of the phenylchalcogen-substituted alkynyl alcohols 11−20 with t-BuOK in t-BuOH provided useful (Z)-2-((phenylchalcogeno)methylene)tetrahydrofurans 21−31 stereoselectively

A Novel Stereoselective Preparation of Various Vinyl Sulfide Derivatives Using β-Alkylthioalkenylselenonium Salts

The treatment of alkynylselenonium salt and various thiophenol derivatives with a catalytic amount of triethylamine gave β-arylthioalkenylselenonium salts in good yields. The alkenylselenonium salts thus prepared reacted with nucleophiles such as acetylides, thiolates, and alkoxides to produce (Z)-β-arylthio-α-functionalized ethenes in high yields. The vinylselenonium salts bearing a hydroxy group on a β-side chain caused intramolecular cyclization upon treatment with sodium hydride to produce medium-membered heterocyclic compounds containing sulfur and oxygen atoms. The reactions giving (Z)-β-arylthio-α-functionalized ethenes would proceed via the formation of selenurane intermediates followed by the ligand coupling reaction

Reactions of Diphenyl(phenylethynyl)selenonium Salts with Active Methylene Compounds and Amides: First Isolation of Oxyselenuranes [10-Se-4(C3O)] as a Reaction Intermediate

The reaction of the diphenyl(phenylethynyl)selenonium triflate 1a with active methylene compounds 5 and t-BuOK in THF gave furan derivatives 6. The [10-Se-4(C3O)] selenuranes 8a and 8b could be isolated from the reactions with benzoylacetonitrile 5f and with 1,3-indandione 5g, respectively, as reaction intermediates. The structures of the selenuranes 8 were elucidated by X-ray crystallography and 77Se high-resolution solid-state NMR spectroscopy. The selenuranes 8 underwent ligand coupling on standing at room temperature or refluxing in chloroform and gave the furan derivatives 6 and the ring-opened product 9. Similarly, the reaction of 1a with benzamide 13a and pivalamide 13d in the presence of NaH in THF afforded oxazole derivatives 14

A Safe and Scalable Procedure for Preparation of α-Picoline–Borane from Sodium Mono-acyloxyborohydrides and α-Picoline

Sodium monobenzoxyborohydride, which is easily prepared from sodium borohydride and benzoic acid in THF in situ, is treated with α-picoline in THF under mild conditions to give α-picoline–borane in an excellent yield. This method can be a practical preparation for α-picoline–borane

Chalcogeno−Morita−Baylis−Hillman Reaction of Enones with Acetals: Simple α-Alkoxyalkylation of Enones

1-[2-(Methylsulfanyl)phenyl]prop-2-en-1-one (1) and the seleno congener (2) reacted with acetals 3 and 21 in the presence of BF3·Et2O to give α-alkoxyalkyl enones 4, 5 and 22, 23 in good yields. When the reaction mixtures were worked up with a saturated NaHCO3 solution instead of Et3N, onium salts 6 and 7 were obtained together with 4 and 5. Reactions with cyclic acetal 14 gave α-(β-hydroxyethoxy) enones 15 and 16 accompanied by dimeric products 17 and 18

Chalcogeno−Morita−Baylis−Hillman Reaction of Enones with Acetals: Simple α-Alkoxyalkylation of Enones

1-[2-(Methylsulfanyl)phenyl]prop-2-en-1-one (1) and the seleno congener (2) reacted with acetals 3 and 21 in the presence of BF3·Et2O to give α-alkoxyalkyl enones 4, 5 and 22, 23 in good yields. When the reaction mixtures were worked up with a saturated NaHCO3 solution instead of Et3N, onium salts 6 and 7 were obtained together with 4 and 5. Reactions with cyclic acetal 14 gave α-(β-hydroxyethoxy) enones 15 and 16 accompanied by dimeric products 17 and 18