• Copper-Catalyzed Propargylic Substitution of Dichloro Substrates: Enantioselective Synthesis of Trisubstituted Allenes and Formation of Propargylic Quaternary Stereogenic Centers
    H. Li, D. Grassi, L. Guénée, T. Bürgi and A. Alexakis
    Chemistry - A European Journal, 20 (50) (2014), p16694-16706
    DOI:10.1002/chem.201404668 | unige:43540 | Abstract | Article HTML | Article PDF
An easy and versatile Cu-catalyzed propargylic substitution process is presented. Using easily prepared prochiral dichloro substrates, readily available Grignard reagents together with catalytic amount of copper salt and chiral ligand, we accessed a range of synthetically interesting trisubstituted chloroallenes. Substrate scope and nucleophile scope are broad, providing generally high enantioselectivity for the desired 1,3-substitution products. The enantioenriched chloroallenes could be further transformed into the corresponding trisubstituted allenes or terminal alkynes bearing all-carbon quaternary stereogenic centers, through the copper-catalyzed enantiospecific 1,1/1,3-substitutions. The two successive copper-catalyzed reactions could be eventually combined into a one-pot procedure and different desired allenes or alkynes were obtained respectively with high enantiomeric excesses.
  • Enantioselective Catalytic Fluorinative Aza-semipinacol Rearrangement
    F. Romanov-Michailidis, M. Pupier, C. Besnard, T. Bürgi and A. Alexakis
    Organic Letters, 16 (19) (2014), p4988-4991
    DOI:10.1021/ol5022355 | unige:41312 | Abstract | Article HTML | Article PDF
 
An efficient and highly stereoselective fluorinative aza-semipinacol rearrangement is described. The catalytic reaction requires use of Selectfluor in combination with the chiral, enantiopure phosphate anion derived from acid L3. Under optimized conditions, cyclopropylamines A were transformed into β-fluoro cyclobutylimines B in good yields and high levels of diastereo- and enantiocontrol. Furthermore, the optically active cyclobutylimines were reduced diastereoselectively with L-Selectride in the corresponding fluorinated amines C, compounds of significant interest in the pharmacological industry.

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