Subsequently, asymmetric versions have been described. In 1994, Murahashi described in a seminal paper the propargylic substitution of monosubstituted alkynes bearing a good leaving group on the propargylic alcohol moiety, where a mechanism through a copper-allenylidene intermediate was postulated. Direct propargylic substitutions have traditionally and efficiently been carried out using the Nicholas conditions but this implies the use of stoichiometric amounts of a cobalt complex.
In this context, we have been particularly interested in the direct substitution of propargylic alcohols, because i) the presence of the alkyne function in the substitution product allows many further synthetic modifications, ii) the challenge of controlling the possible competition between substitutions at the propargylic and/or the allenic positions, and iii) compared to allylic and benzylic substitutions these reactions have been studied to a far lesser extent. Since some pioneering work using stoichiometric amounts of Lewis acid catalysts, much effort has been devoted to this goal. For economic, environmental and practical reasons it is therefore of interest to develop new experimental conditions for the direct substitution of activated alcohols such as tertiary, allylic, benzylic or propargylic ones. In the field of nucleophilic substitution reactions, leaving groups are mostly often obtained from alcohols but initially require their transformation to better leaving groups such as sulfonates or acetates.
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