Carbonyl Propargylation and Allenylation with 2-Propynyl Mesylates, Tin(IV) Iodide, and Tetrabutylammonium Iodide Controlled by Either a Steric Effect or Coordination Effect

A combination of tin(IV) iodide and tetrabutylammonium iodide can be used for propargylation or allenylation of aldehydes with 2-propynyl mesylates in dichloromethane. 1-Methyl-2-propynyl mesylate or 2-butynyl mesylate results in propargylation or allenylation controlled by the steric effect of the 1- or 3-methyl group, and 3-trimethylsilyl-2-propynyl mesylate results in propargylation controlled by the coordination of triiodostannate to silane.