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Cyclization of Nonterminal Alkynic β-Keto Esters Catalyzed by Gold(I) Complex with a Semihollow, End-Capped Triethynylphosphine Ligand

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journal contribution
posted on 06.11.2008, 00:00 by Hideto Ito, Yusuke Makida, Atsuko Ochida, Hirohisa Ohmiya, Masaya Sawamura
A cationic gold(I) complex with a semihollow-shaped trialkynylphosphine catalyzed 5-exo-dig and 6-endo-dig cyclizations of various internal alkynic β-keto esters, showing a marked advantage over a gold(I)−PPh3 complex with respect to the rates of the reactions and the product yields. It is proposed that the gold-bound alkynic substrate in a catalytic pocket must be somewhat folded and that such a steric effect makes the carbon−carbon bond formation entropically more favorable.