Sulfinate-Organocatalyzed (3+2) Annulation Reaction of Propargyl or Allenyl Sulfones with Activated Imines
Résumé
The synthesis of 4‐sulfonyl‐3‐pyrrolines, from a propargylic sulfone and activated imines, is described. The annulation is initiated by sodium benzenesulfinate as organocatalyst, which allows isomerization of the alkynyl precursor to the analogous allene. A proof of concept towards an asymmetric version involving an unprecedented enantiopure sulfinate–ammonium cooperative ion pair was then highlighted (ee up to 41 %).
An operationally simple methodology for the synthesis of 4‐sulfonyl‐3‐pyrrolines is described using a propargylic sulfone and N‐sulfonyl imines as substrates. This annulation process is initiated by an arenesulfinate organocatalyst, which allows a smooth isomerization of the alkynyl precursor into the corresponding allene, followed by the generation of a highly reactive allyl sulfone anion. An asymmetric version involving an unprecedented enantiopure sulfinate–ammonium cooperative ion pair (PhSO2– R4N+*) was investigated. A proof‐of‐concept, with enantiomeric excesses of up to 41 %, was obtained according to a preliminary screening of commercially available chiral phase‐transfer catalysts.