One-Pot Nucleophilic Organocatalytic Enantioselective [8 + 2] Cycloadditions of Photogenerated Ketenes with Triflate Tropolones

This work presents diazoketones as ketene precursors under photochemical conditions, in conjunction with an isothiourea catalyst, to enable an enantioselective [8 + 2] cycloaddition with triflate-substituted tropolones affording 7,5-fused lactone scaffolds. The cycloadducts are obtained in up to 99% yield with up to excellent diastereoselectivity (>20:1 d.r.) and enantioselectivity (up to 99% ee). Furthermore, it is demonstrated that the 7,5-fused lactone can undergo diverse attractive transformations.