Synthesis of (E)-olefin dipeptide isosteres

Trans-Selective Conversions of γ-Hydroxy-α,β-Alkynoic Esters to γ-Hydroxy-α,β-Alkenoic Esters

Gamma-hydroxy-alpha,beta-acetylenic esters are used as precursors to prepare gamma-hydroxy-alpha,beta-alkenoic esters by means of trans-selective additions of two hydrogen atoms or one hydrogen atom and one iodine atom across the triple bonds. These methods allow for the preparation of beta-substituted and alpha,beta-disubstituted alkenoic esters in highly stereoselective manners. [reaction--see text]

Palladium(0)-Catalyzed Isomerization Reactions of Aziridines Bearing an alpha,beta-Unsaturated Ester Group: A Thermodynamic Preference for Chiral Alkyl (2E)-4,5-cis-4,5-Epimino-N-(alkyl- or arylsulfonyl) 2-Enoates over the Other Three Stereoisomers

Palladium(0)-catalyzed reactions of five sets of four stereoisomeric 4,5-epimino-N-(methanesulfonyl) or -N-(arylsulfonyl) 2-enoates reveal that 4,5-cis-(2E)-isomers are thermodynamically more stable than other isomers, in accord with calculations. A highly stereoselective synthesis of (E)-alkene dipeptide isosteres having the desired stereochemistries from unwanted stereoisomeric 4,5-epimino-N-(arylsulfonyl) 2-enoates is also presented.