Ruthenium-Catalyzed Aromatization of Enediynes via Highly Regioselective Nucleophilic Additions on a pi-Alkyne Functionality.A Useful Method for the Synthesis of Functionalized Benzene Derivatives

摘要

TpRu(PPh_3)(CH_3CN)_2PF_6 (10 mol %) catalyst effected the nucleophilic addition of water,alcohols,aniline,acetylacetone,pyrroles,and dimethyl malonate to unfunctionalized enediynes under suitable conditions (100 deg 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.