Rhodium(i)-catalyzed Pauson–Khand-type reaction using formic acid as a CO surrogate: an alternative approach for indirect CO2 utilization

Abstract

Formic acid is found to be an ideal CO surrogate for the rhodium(I)-catalyzed Pauson–Khand-type (PK-type) reaction of various substituted 1,6-enynes to afford bicyclic cyclopentenones in moderate to good yields. High TON value of up to 263 and good results in the gram-scale experiment were also obtained, demonstrating the efficacy of this methodology. In addition, heterocyclic molecules of pharmaceutical importance were also furnished via inter- or intra-molecular hetero-PK-type reactions, further broadening the application of current strategy. In this protocol, formic acid was utilized as a bridging molecule for the conversion of CO₂ to CO, since formic acid is manufactured via catalytic hydrogenation of CO₂ and releases CO in the presence of acetic anhydride readily. Therefore, this methodology represents a green and indirect approach for chemical valorization of CO₂ in the preparation of value-added compounds.