Lithium-phenylacetylene adducts

Qudguiner s group lithiated a sym-disubstituted pyrazine, 2,6-dimethoxypyrazine (43), with lithium 2,2,6,6-tetramethylpiperidine (LTMP). The resulting lithiated intermediate was quenched with h to give 3-iodo-2,6-dimethoxypyrazine (44) and 3,5-diiodo-2,6-dimethoxypyrazine (45) [35]. Iodide 44 was then coupled with phenylacetylene to provide adduct 46. 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

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