Ruthenium-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohols with Oxygen-,Nitrogen-,and Phosphorus-Centered Nucleophiles

摘要

The scope and limitations of the ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with heteroatom-centered nucle-ophiles are presented.Oxygen-,nitrogen-,and phosphorus-centered nucleo-philes such as alcohols,amines,amides,and phosphine oxide are available for this catalytic reaction.Only the thio-late-bridged diruthenium complexes can work as catalysts for this reaction.Results of some stoichiometric and catalytic reactions indicate that the catalytic propargylic substitution reaction proceeds via an allenylidene complex formed in situ,whereby the attack of nucleophiles to the allenylidene C_(gamma) atom is a key step.Investigation of the relative rate constants for the reaction of propargylic alcohols with several para-substituted anilines reveals that the attack of anilines on the allenylidene C_(gamma) atom is not involved in the rate-determining step and rather the acidity of conjugated anilines of an al-kynyl complex,which is formed after the attack of aniline on the C_(gamma) atom,is considered to be the most important factor to determine the rate of this catalytic reaction.The key point to promote this catalytic reaction by using the thiolate-bridged diruthenium complexes is considered to be the ease of the ligand exchange step between a vi-nylidene ligand on the diruthenium complexes and another propargylic alcohol in the catalytic cycle.The reason why only the thiolate-bridged diruthenium complexes promote the ligand exchange step more easily with respect to other monoruthenium complexes in this catalytic reaction should be that one Ru moiety,which is not involved in the allenylidene formation,works as an electron pool or a mobile ligand to another Ru site.The catalytic procedure presented here provides a versatile,direct,and one-step method for propargylic substitution of propargylic alcohols in contrast to the so far well-known stoichiometric and stepwise Nicholas reaction.