Science of Synthesis

Krueger, A., Science of Synthesis, (2008) 43, 489.

Potassium and silver salts of α-halo-β,β-diarylacrylic acids ‌64‌ or α-halocinnamic acids ‌64‌ (Ar2 = H) rearrange to (di)arylacetylenes (typical yields ∼50%, in some cases up to 90%) with cleavage of carbon dioxide and metal halide when heated in dimethyl sulfoxide, hexamethylphosphoric triamide, or without a solvent (‌Scheme 26‌).[‌58‌,‌101‌,‌102‌] The metal has a major influence on the mechanism of the reaction. In the case of decomposition of the potassium salt of the diaryl compound in dimethyl sulfoxide, the ratio between the alkyne ‌65‌ and the vinyl chloride ‌66‌ is 19:72, whereas the respective silver salt yields a 62:11 mixture.[‌101‌] It has been argued that in the latter case a radical pair ‌67‌ is formed instead of the intermediate carbanion, thus hindering the protonation to the vinyl chloride.[‌102‌] On the other hand, the thermolysis of the potassium salt of 3-(biphenyl-4-yl)-2-chloro-3-phenylacrylic acid in hexamethylphosphoric triamide at 160–190°C gives 90% of the corresponding alkyne.[‌58‌] The decomposition of α-chlorocinnamic acid not only yields the alkyne in good yields, but also 1,4-diphenylbuta-1,3-diyne and some polymeric material.[‌102‌] The diyne is most likely formed by a Glaser-like coupling reaction.[‌58‌,‌101‌,‌102‌]

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References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8e, 888.