Titanium-promoted Intramolecular Photoenolization/Diels-Alder Reaction to Construct Polycyclic Terpenoids: Formal Synthesis of Mycoleptodiscin A

The Summary of main observation and conclusion A titanium-promoted intramolecular photoenolization/Diels-Alder (PEDA) reaction was developed to construct the core skeleton of aromatic polycyclic terpenoids bearing an all-carbon quaternary center on the benzylic position. Titanium(IV) isopropoxide [Ti(Oi-Pr)(4)] plays a key role during the photo cycloaddition, which may help to accelerate the interaction between dienophile and the stereo-hindered diene species as well as control the diastereoselectivity. This photolysis provides a new solution for the stereospecific formation core structures of aromatic abietane diterpenoids and sesquiterpenoids, which have multiple functional groups for the further transformations. As a synthetic application, it was successfully used in the synthesis of indolosesquiterpenoid mycoleptodiscin A.