Sulfinate-Organocatalyzed (3+2) Annulation Reaction of Propargyl or Allenyl Sulfones with Activated Imines

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.