Cyclobutenes as Isolable Intermediates in the Gold(I)-Catalysed Cycloisomerisation of 1,8-Enynes

The gold(I)-catalysed isomerisation of 1,8-enynes allows the efficient synthesis of functionalised bicyclo[5.2.0]nonenes. Notably, these cyclobutenes derivatives can be isolated as reactive intermediates that could undergo subsequent gold(I)-catalysed transformations such as isomerisation, fragmentation or ene reaction to furnish more structurally complex products. This study also provides useful information related to the mechanism leading to metathesis-type derivatives, examples of which were shown to be produced, in the present case, by a gold(I)-catalysed ring fragmentation of the cyclobutene moiety.