Terminal akyne

Reproduced from Mukherjee N, Ahammed S, Bhadraa S, Ranu BC. Solvent-fiee one-pot synthesis of 1,2.3-triazole derivatives by the Click reaction of akyl halides or ary boronic ackis, sodium azide and terminal akynes over a Cu/AlyOs surface under ball-milling. Green Chem 2013 15 389-97 with permission from the Royal Society of Chemistry. 

The Pauson-Khand reaction is a cobalt-mediated cycloaddition of an alkene, an alkyne, and carbon monoxide to yield cyclopentenones." When employing reactive precursors (acetylene or terminal akynes), the reaction proceeds in excellent yield however, chemoselectivity issues can contribute to decreased reaction yields and unwanted side products in cases where the alkyne component competitively undergoes cyclotrimerization... 

As expected, additions to alkynes are also subject to control by polar functions nearby. Thus, nucleophilic attack on trifluoromethylacetylene [116], cyanoacetylene [137], and ethylthioacetylene [138] occurs at the terminal jp-hybridized carbon atom, the substituent at the other end of the triple being an acceptor in all cases. This behavior is to be contrasted with the mode of addition on ethoxyacetylene [3 39], aminoacetylenes [120], The vinylogue, 4-dimethyl-aminobut-3-en-l-yne [121], reacts with aniline at the internal position of the akyne linkage. However, a 2 1 regiose-lectivity, favoring the methanol adduct predicted by the polarity alternation rule, has been observed for the addition of jV,jV-bis(trifluoromethyl)ethynylamine [122], It is not known whether steric factors play a role in the decreased regioselectivity. 

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