FRITSCH-BUTTENBERG-WIECHEL Acetylene

FRITSCH BUTTENBERG - WIECHELL Acetylene Synthesis Alpha elimination from haloethylenes leading via carbene rearrangement to acetylenes... 

FRIEDLANDER Quinoline synthesis t32 FRIES Phenol ester rearrangement 133 FRITSCH. BUTTENBERG - WIECHELL Acetylene synthesis 134... 

This carbenoid undergoes a Fritsch-Buttenberg-Wiechell rearrangement84 when warmed at room temperature, to give the internal acetylene derivative (equation 58)85. 

An a-elimination of hydrogen halide or halogene from a sp2 carbon leads formally to a vinyl carbene species which may eventually rearrange to the corresponding acetylene. This reaction was discoverd in 1894 and is called Fritsch-Buttenberg-Wiechell rearrangement159). 

The Fritsch-Buttenberg-Wiechell rearrangement provides a method to expand a cyclic ketone to a cyclic acetylene with an additional carbon atom in the ring [34]. The ketone is first converted to a vinyl bromide or a vinylidene dibromide, from which the corresponding vinylidene carbene is produced with butyllithium. The vinylidene carbene then rearranges to a cyclic alkyne (Scheme 8-10). 

Typical substrates for Fritsch-Buttenberg-Wiechell rearrangements are chloro-ethenes and ge/w-dibromoethenes. They are readily prepared by Wittig reaction from the corresponding ketones. The method offers a versatile entry to aromatic or heterocyclic acetylenes. Moreover, ethynyl groups can embark also on 1,2-migrations, thus, making simple or functionalized diynes and triynes (e.g., 321) accessible (Scheme 1-250). ... 

P. Fritsch, Ann. 279, 319 (1894) W. P. Buttenberg, ibid. 327 H. Wiechell, ibid. 332. Carbene-mediated rearrangement of 1,1-diary 1-2-haloethylenes to diaryl acetylenes ... 

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