TpRu(PPh3)(CH3CN)2 PF6 (10 mol %) catalyst effected the nucleophilic addition of water, alcohols, aniline, acetylacetone, pyrroles, and dimethyl malonate to unfunctionalized enediynes under suitable conditions (100 degrees C, 12-24 h) and gave functionalized benzene products in good yields. In this novel cyclization, nucleophiles very regioselectively attack the internal C1' alkyne carbon of enediynes to give benzene derivatives as a single regioisomer. Experiments with methoxy substituents exclude the possible involvement of naphthyl cations as reaction intermediates in the cyclization of (o-ethynylphenyl) alkynes. Deuterium-labeling experiments indicate that the catalytically active species is ruthenium-pi-alkyne rather than ruthenium-vinylidene species. This hypothesis is further confirmed by the aromatization of o-(2'-iodoethynyl)phenyl alkynes with alcohols. We propose a nucleophilic addition/insertion mechanism for this nucleophilic aromatization on the basis of a series of experiments.
Ring closure reactions O 0130Ruthenium-Catalyzed Aromatization of Enediynes via Highly Regioselective Nucleophilic Addition on a π-Alkyne Functionality. A Useful Method for the Synthesis of Functionalized Benzene Derivatives. -A new method for nucleophilic aromatization of unfunctionalized, unstrained enediynes is presented. Experimental evidence is given for the presence of a ruthenium-π-alkyne species rather than a ruthenium-vinylidene as the catalytically active species. -(ODEDRA, A.; WU, C.-J.; PRATAP, T. B.; HUANG, C.
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