Generation of Cycloalkylidene Carbenes via Exo-Type Cyclization of Alkynyllithiums Bearing Remote Leaving Group
摘要:
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-lithiod-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 cyclopentylidene carbene and cyclohexyne as intermediates is clearly demonstrated by trapping experiments with cyclohexene land triethylsilane) and with 1,3-diphenylisobenzofuran, respectively. Alkynyllithiums derived from 3-butynyl and 6-heptynyl p-fluorobenzenesulfonates (19a,b) undergo a similar exo-type cyclization to give cyclopropylidene and cyclohexylidene carbenes, respectively.
Cyclohexynes as intermediates in a novel endo-cyclization of alkynylzincates derived from 5-hexynyl tosylates
作者:Toshiro Harada、Takeshi Otani、Akira Oku
DOI:10.1016/s0040-4039(97)00481-4
日期:1997.4
The pi-type endo-cyclization of metal acetylides to form cyclohexynes was observed for the first time in the reaction of alkynylzincates derived from 5-hexynyl tosylates. The endo-cyclization took place in competition with exo-cyclization, leading to the formation of 1-(cyclopentylidene)alkylzincs. (C) 1997 Elsevier Science Ltd.