Synthèse asymétrique et configuration absolue de dihydropyranes substitués, par hétérocycloaddition intermoléculaire d'éthers vinyliques chiraux
摘要:
The alkyl vinyl ethers 2b-8b (deriving from the alcohols 2a-8a) smoothly reacted with methyl E-benzylidenepyruvate 10 in the presence of catalytic amounts of Eu(fod)(3) or Yb(fod)(3) in refluxing hexane, thus leading to the dihydropyran endo adducts 13-19 in high yields (80-95%). The endo-cycloadducts 13-17 were obtained with diastereofacial selectivities (ds) ranging from 76/24 to 87.5/12.5. Asymmetric induction was found to culminate with the vinyl ether (-)-7b deriving from n-butyl (R)-(-)-mandelate : the best ds (92.5/7.5) was obtained for the corresponding adduct 18 after 6 days at room temperature. The absolute configurations of the major isomers of the dihydropyrans 16-18, 20 and 21 were established by oxydative degradation to optically active alpha-phenylsuccinic acid derivatives.
Two Types of Cross-Coupling Reactions between Electron-Rich and Electron-Deficient Alkenes Assisted by Nucleophilic Addition Using an Organic Photoredox Catalyst
Two types of photoreactions between electronically differentiated donor and acceptor alkenes assisted by nucleophilic addition using an organic photoredox catalyst efficiently afforded 1:1 or 2:1 cross-coupling adducts. A variety of alkenes and alcohols were employed in the photoreaction. Control of the reaction pathway (i.e., the formation of the 1:1 or 2:1 adduct) was achieved by varying the concentration
A novel and convenient palladium catalytic system for the synthesis of α‐amino acid esters from simple starting materials is reported. Hydrogenperoxide not only acts as the green oxidant, but also as the oxygen source. This strategy for the conversion of amines and vinyl ethers into highly functionalized and structurally diverse α‐amino acid esters is characterized by the simplicity of the experimental