engleski

Generation and Trapping of 7-Norbornylidenecarbene and Heptacyclic Analog of this Alkylidenecarbene

Reaction of 7-(dibromomethylene) norbornane (2) wi th n-BuLi resulted in alpha-elimination of Br-2 with concomitant formation of 7-norbornylidenecarbene (4a). When this reaction was performed in the absence of an alkene trapping agent, the col-responding cumulated triene, 5, was produced (47% yield). When 4a was generated in the presence of norbomadiene, the corresponding [2 + 2] cycloadduct, 7, was formed in 82% yield. Alkylidenecarbene 4a thus generated in the presence of cis-2-butene resulted in stereospecific formation of the corresponding cis cycloadduct, 8 (74% yield), thereby suggesting that 4a functions as a singlet unsaturated cal bene in this reaction. Similar reactions of 7-(dibromomethylene)-HCTD (11) with n-BuLi performed (i) in the absence of added alkene and (ii) in the presence of cyclohexene resulted in the formation of cumulated triene 14 (69% yield) and [2 + 2] alkylidenecalbene-alkene cycloadduct 15 (51%, yield), respectively. We find no evidence for the formation of cycloalkynes (i.e., 4b or 13b) in any of the reactions reported herein. ============================================================= Reakcijim 7-dibrommetilen)norbornana s n-BuLi dolazi do eliminacije Br2 i istovremenog formiranja 7-norbornilkarbena. Kad se reakcija provede bez prisustva alkenskog "traping" agensa dobije se trien. Kad se reakcija provede u prisutnosti norbornandiena dobije se 2+2 cikloadukt.

Norbornane; Carbene

nije evidentirano