Alkylation of Terminal Alkynes under Zinc Lewis Acid Catalysis and Its Mechanistic Studies
With a zinc Lewis acid catalyst and proton sponge in toluene, terminal alkynes were found to undergo the alkylation by alkyl triflates to provide unsymmetrical internal alkynes. This is the first example that a simple alkyl chain other than benzylic and norbornyl units can be introduced onto the alkynyl carbon atom under Lewis acid catalysis. Mechanistic studies revealed that the activation of the alkyne by the zinc Lewis acid and proton sponge is the trigger of the reaction to give a monoalkynylzinc species, which successively reacts with the alkyl triflate to afford the internal alkyne. A radical pathway is unlikely in this system. (Figure presented.).
Kolbe Synthesis of Unsaturated Pheromones by Coelectrolysis with 5-Alkynoic Acids
The alkynoic acids 5a - g are synthesized by coelectrolysis of 5-alkynoic acids 2a - c with dicarboxylic monoesters 3a - d.By reduction, Lindlar-hydrogenation, and acetylation these are converted into pheromones such as (Z)-11-hexadecenyl acetate (7b), the pheromone of Mamestra brassicae. 2a - c can be prepared by alkynylation of 1-bromo-3-chloropropane to 1a - c, substitution by cyanide and hydrolysis.
Seidel, Wolfgang,Schaefer, Hans J.
p. 3898 - 3903
(2007/10/02)
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