Abstract Reaction of 6-bromo-1-trimethylsilyl-1-hexyne with magnesium affords the corresponding Grignard reagent whose C-Mg bond intramolecularly adds to the trimethylsilylacetylene moiety in 5-Exo-Dig manner and suprafacially. The reaction can be applied to the synthesis of some cycloalkanes having stereo-defined alkylidene substituents.
