Organocatalyzed Enantioselective Protonation of Silyl Enol Ethers: Scope, Limitations, and Application to the Preparation of Enantioenriched Homoisoflavones
In the present work, enantioselective protonation of silylenolethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchonaalkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved
[reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available aminoacid derivatives as chiral proton sources. Among the aminoacid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in
Enantioselective Fluorination Mediated by Cinchona Alkaloid Derivatives/Selectfluor Combinations: Reaction Scope and Structural Information for <i>N</i>-Fluorocinchona Alkaloids
Cinchona-alkaloid/Selectfluor combinations efficiently fluorinate a variety of carbonyl compounds in a highly enantioselective manner to furnish chiral alpha-fluorocarbonyl compounds. The DHQB/Selectfluor combination is effective for the enantioselective fluorination of indanones and tetralones 1 in up to 91% ee. The first enantioselective syntheses of chiral derivatizing reagents 3 was accomplished with high ee and in
several limitations in both chemical yields and enantioselectivities of the fluorinated products. We present here the background of our personal story of the enantioselectivefluorination reaction and some successful applications of the methods to the design and synthesis of biologically active products. Two novel approaches using cinchonaalkaloid/Selectfluor® combinations and chiral ligands/metal complexes
Regioselective C-deuteration of a series of Endocyclic enolates (derived from cyclic arylketones) was efficiently achieved by quenching the corresponding “base-free” enolate in the presence of a suitable deuterium source. We discuss the structural nature of the deuteriumdonor and comment on the use of additives within this deuteration step.