Zinc catalysis alkynylation

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

Zinc catalysts have shown a major increase in their possible applications. Some examples of catalysis using halide complexes, including immobilized catalytic systems, have been discussed in Section 6.8.8. Some areas such as asymmetric alkynylation of aldehydes have been recently reviewed.930... 

C2-alkynylation of (benzo)furans 7 and 12 was achieved selectively under gold catalysis with hypervalent ethynylbenziodoxolone reagents (TIPS-EBX (10)) (Scheme 3) (2013AGE6743, 2013BJOC1763). Under mild conditions, a broad set of substituted furans 7 and benzofiirans 12 were successfully alkynylated (11 and 13) albeit for the latter a higher reaction temperature and an additional (super)stoichiometric zinc salt was needed. Waser has shown the instantaneous formation of bis(triisopropyl-silyl)diyne via reaction of TIPS-EBX 10 with AuCl (2012CEJ5655). Therefore the mechanism likely involves oxidative addition of Au with TIPS-EBX 10 followed by electrophUic C—H auration, with elimination of 14 and reductive elimination (Scheme 4). 

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