Asymmetric Organocatalytic Synthesis of Sulfone‐Containing (Dihydro)pyrans via Formal (4 + 2)‐Cycloadditions of Allenylsulfones or Propargylsulfones and Michael Acceptors
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Asymmetric isochalcogenourea-catalyzed cycloadditions of allenylsulfones and propargylsulfones with Michael acceptors allow for the highly selective syntheses of sulfone-containing dihydropyrans and 4H-pyrans.
Abstract
The activation of electron-poor allenes with Lewis's base catalysts allows for unique transformations and chiral isochalcogenoureas were recently introduced as powerful catalysts for allenoate-based (4 + 2)-cycloadditions. We herein report the use of these catalysts for the activation and control of allenylsulfones and propargylsulfones for asymmetric (4 + 2)-cycloadditions with Michael acceptors. Based on the reaction conditions, this strategy either gives access to sulfone-containing dihydropyrans or analogous 4H-pyrans with high yields and excellent levels of enantioselectivities (up to > 99:1 er).
