Alkynylhalocarbenes 4.~* Generation of (alk-1-ynyl)halocarbenes from 3-substituted 1,1,1,3-tetrahalopropanes under the action of bases~**

摘要

When treated with KOH under phase-transfer catalysis or with Bu~tOK, 3-substituted (alkyl or phenyl) 1,1,3-tribromo-1-fluoropropanes 1a-c exclusively generate previously un-known (alk-1-ynyl)fluorocarbenes 5a-c, which react with olefins to give 1-(alk-1-ynyl)-1-fluorocyclopropanes 6a-h in 12-69% yields. Under analogous conditions, 3-alkyl- and 3-aryl-3-bromo-1,1,1-trichloropropanes 2a-c selectively afford (alk-1-ynyl)-1-chlorocyclo-propanes 8a-k in 35-70% yields. (Phenylethynyl)chlorocarbene 7a is also selectively generated from 1,1,1,3-tetrachloro-3-phenylpropane (3a) upon its treatment with Bu~tOK. With an excess of 2,3-dimethylbut-2-ene or 2-methylpropene, carbene 7a yields 1-chloro-1-(phenyl-ethynyl)chclopropanes 8a or 8c, respectively. In contrast, 1,1,1,3-tetrachloroheptane 3b and 3-alkyl-and 3-phenyl-1,1,1,3-tetrabromopropanes 4a,c,f react with bases in the pesence of olefins to give, along with the correspondng 1-(alk-1-yhyl)-1-halocyclopropanes 8a,c,d and 11a-f, vinylidenecyclopropanes 12a,c-g, which suggests the generation, under these conditions, both (alk-1-ynyl)halocarbenes 7b and 9a-c and vinyllidenecarbenes 10 and 11a-c. The composition and structures of intermediate products in the reactions of tetrahalides 1b, 2a, 2b, 3a, and 3b with Bu~tOK were determined and the mechanisms for carbene generation in these reactions were proposed.