Tandem Enyne Metathesis-Diels−Alder Reaction for Construction of Natural Product Frameworks

Enynes connected through aromatic rings are used as substrates for metathesis reactions. The
reactivity of three ruthenium carbene complexes is compared. The resulting 1,3-dienes are suitable
precursors of polycyclic structures via a Diels−Alder process. Some domino RCM-Diels−Alder
reactions are performed, suggesting a possible beneficial effect of the ruthenium catalyst in the
cycloaddition process. Other examples require Lewis acid cocatalyst. When applied to aromatic
ynamines or enamines, a new synthesis of vinylindoles is achieved. Monitorization of several
metathesis reactions with NMR shows the different behavior for ruthenium catalysts. New carbenic
species are detected in some reactions with an important dependence on the solvent used.