Mechanistic insight into cobalt-mediated [2+2+2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2π partners

The molecular complexity of recently reported cobalt(iii) polycyclic complexes, resulting from an intramolecular formal (2 + 2 + 3) cycloaddition reaction on an enediyne containing a lactone moiety, has prompted us to computationally review the mechanisms of cobalt cycloaddition reactions with gamma-alkylidenebutenolide or gamma-alkylidenebuterolactam as 2 pi partners. Computed mechanisms are compared, leading to either cobalt(iii)- or cobalt(i)-spiro complexes depending of both the nature of the reaction (intra- vs. intermolecular pathway) and the nature of the 2 pi partner (gamma-alkylidenebutenolide vs. gamma-alkylidenebuterolactam). These proposed mechanisms are supported by experiments, allowing us to report the synthesis and characterization of the predicted compounds. A computationally revised mechanism discloses the role of the 2 pi partner in Co-mediated cycloaddition reactions for lactone and lactam substrate derivatives. This leads to the successful synthesis of spiro-lactone and spiro-lactam complexes.

Automated summary

This study computationally investigates the molecular complexity of cobalt(iii) polycyclic complexes and examines the mechanisms and role of 2 pi partners in cobalt-mediated cycloaddition reactions. The proposed mechanisms were supported by experiments and predicted compounds were successfully synthesized.