Mechanistic insight into cobalt-mediated [2+2+2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2p 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 and experimentally investigated the mechanism of cobalt cycloaddition reactions. Based on the nature of the reaction and the nature of the 2π partner, spiro-lactone and spiro-lactam complexes were successfully synthesized.