Unexpected Selectivity of Intramolecular [3+2] Cycloaddition of Trimethylenemethane (TMM) Diyl toward Total Synthesis of Conidiogenone B

In the course of a study toward a total synthesis of conidiogenone B through TMM diyl‐mediated tandem cycloaddition reaction, unexpected regioselectivity for a bridged isomer was observed. The synthetic and computational studies with model compounds revealed that regioselectivity can be rendered by changing substitution patterns on the TMM diyl moiety and the olefin moiety by altering the activation energy of cycloaddition reaction through a singlet TMM diyl pathway.