Propargyl esters with terminal alkynes

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... 

Computational studies performed on both reactions, leading either to dienyl esters or to alkenylidenecyclobutenes, show that the biscarbene ruthenium intermediate requires a high activation energy to produce the cyclobutadiene complex from terminal alkynes whereas with propargyl alcohols this step occurs readily [25],... 

An original, and versatile route toward ulosonic acids has been recently elaborated by Wu et al. [103,104,105], It based on a simple introduction of a-keto acid moiety via propargylation of suitable monosaccharides derived aldehydes and subsequent oxidation of the terminal alkynes. As it is exemplified by preparation of KDO, coupling of 61 with 3-bromopropyne gave the a fr-adduct 139 (Scheme 30). Its bromination using NBS/AgNC>3 provided the bromoalkyne 140, which on reaction with KMnC>4 afforded the desired a-keto acid ester, easily convertible into the anomeric mixture of KDO derivatives 143. The yield of all intermediates were very high. 

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