Consecutive Rh(I)-catalyzed Alder-ene/Diels–Alder/Diels–Alder reaction sequence affording rapid entry to polycyclic compounds

Conversion of acyclic allenynes to polycyclic compounds using consecutive transition metal catalyzed carbon–carbon bond forming reactions in a single chemical operation is described. Reaction of an allenyne with a Rh(I) catalyst affords a cross-conjugated triene via a formal Alder-ene reaction. The triene then participates in a Rh(I)-catalyzed intramolecular [4+2] cycloaddition reaction to generate a new conjugated diene. An external dienophile is added to this diene which then undergoes a second [4+2] cycloaddition reaction to afford a complex polycyclic ring system. This reaction sequence demonstrates the synthetic potential of allenynes and cross conjugated trienes and highlights the rapid increases in molecular complexity that are possible by one-pot sequential transition metal catalyzed carbon–carbon bond forming reactions.