Abstract: The reaction of 3-ethynyl-2, 2, 4, 4-tetramethyl-3-pentyl acetate (5) with potassium tert-butoxide and olefins gave di-tert-butylvinylidenecyclopropanes. The relative rates of reaction of the intermediate di-tert-butylvinylidene-carbene with olefins were determined and compared with previously obtained rates of reaction of the dimethylvinylidenecarbene. Arguments are presented which suggest that the carbenes are uncomplexed in the ...