The reaction of 5-hexynyl tosylate (3a) with alkynyllithium (RC⋮ CLi; R= Ph, TMS) gives enynes 5 and 6. The reaction proceeds through a mechanism involving a novel exo-type cyclization of 6-lithio-5-hexynyl tosylate to form cyclopentylidene carbene. Enyne 6 is produced by the addition of RC⋮ CLi to the carbene, whereas rearrangement of the carbene to cyclohexyne followed by carbolithiation with RC⋮ CLi gives enyne 5. The formation of ...
