Propargylic metal derivatives rearrangement

In 1998 it was revealed that allenylidene-ruthenium complexes, arising simply from propargylic alcohols, were efficient precursors for alkene metathesis [12], This discovery first initiated a renaissance in allenylidene metal complexes as possible alkene metathesis precursors, then it was observed and demonstrated that allenylidene-ruthenium complexes rearranged into indenylidene-ruthenium intermediates that are actually the real catalyst precursors. The synthesis of indenylidene-metal complexes and their efficient use in alkene metathesis are now under development. The interest in finding a convenient source of easy to make alkene metathesis initiators is currently leading to investigation of other routes to initiators from propargylic derivatives. 

In parallel, since the first preparation of allenylidene-metal complexes in 1976, the formation of these carbon-rich complexes developed rapidly after the discovery, in 1982, that allenylidene-metal intermediates could be easily formed directly from terminal propargylic alcohols via vinylidene-metal intermediates. This decisive step has led to regioselective catalytic transformations of propargylic derivatives via carbon(l)-atom bond formation or alternately to propargylation. Due to their rearrangement into indenylidene complexes, metal-allenylidene complexes were also found to be catalyst precursors for olefin and enyne metathesis. 

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