Introducing TeHyperBTM as an Organocatalyst for (4 + 2)‐Cycloadditions of Michael Acceptors with Allenoates, But‐2‐ynoates or Allenylphosphonates

TeHyperBTM [= (2 S ,3 R )‐3‐isopropyl‐2‐phenyl‐3,4‐dihydro‐2 H ‐benzo[4,5][1,3]tellurazolo[3,2‐a]pyrimidine] is introduced as a novel, highly effective, chiral, Lewis basic isochalcogenourea organocatalyst. Compared to its established sulphur‐ and selenium‐based homologues HyperBTM and SeHyperBTM, the increased nucleophilicity and Lewis basicity of TeHyperBTM directly impact its catalytic performance by increasing reaction rates and often also improving enantioselectivities for organocatalytic (4 + 2)‐cycloadditions between Michael acceptors and electron‐deficient allenes or alkynes. Furthermore, less reactive reagents, such as diethyl allenylphosphonate or ethyl but‐2‐ynoate, that were not sufficiently activated by HyperBTM and SeHyperBTM catalysts, underwent smooth (4 + 2)‐cycloadditions with Michael acceptors when using TeHyperBTM as the catalyst, which underscores the high catalytic potential of this novel chiral highly nucleophilic Lewis base.