REACTION-MECHANISM OF COPPER(I) CATALYZED HEAD-TO-HEAD DIMERIZATION OF 1-ALKYNES - AN EXPERIMENTAL AND THEORETICAL-STUDY

The Strauss reaction is regioselective and unique for the head-to-head coupling of terminal acetylenes. For the success of the catalytic con version, the presence of copper(I) carboxylate is necessary. The corre sponding carboxylic acid may be used pure, as solvent, or diluted in n on-nucleophilic solvents. However, its presence in excess is also nece ssary. The formation of the product, 1,4-dialkylenynes, shows some ste reoselectivity. The E isomer is always dominant in the mixture, but th e E/Z ratio may be manipulated by the steric effects of the R groups o f the carboxylic acid and of the monomers as well. The nucleophilic so lvents such as H2O, ROH and phosphine ligands inhibit the catalytic re action. The isolated products are the copper acetylides or its phosphi ne complexes, respectively. Mesitylacetylene and p-nitrophenylacetylen e do not undergo the catalytic conversion. However, the former gives t he cross-product with phenylacetylene, The possible mechanism of the r eaction is discussed and the suggested pathway is supported with compu tational calculations. Copyright (C) 1996 Elsevier Science Ltd