Enantioselective Synthesis of Distorted π-Extended Chiral Triptycenes Consisting of Three Distinct Aromatic Rings by Rhodium-Catalyzed [2+2+2] Cycloaddition

The enantioselective synthesis of distorted pi-extended chiral triptycenes, consisting of three distinct aromatic rings, has been achieved with high ee value of 87 % by the cationic rhodium(I)/segphos complex-catalyzed enantioselective [2+2+2] cycloaddition of 2,2 '-di(prop-1-yn-1-yl)-5,5 '-bis(trifluoromethyl)-1,1 '-biphenyl with 6-methoxy-1,2-dihydronaphthalene followed by the diastereoselective Diels-Alder reaction and aromatization. Demethoxy derivatives were also synthesized by the C-O bond cleavage. In this synthesis, the use of the electron-deficient diyne and the electron-rich alkene is crucial to suppress the undesired strain-relieving carbocation rearrangement and stabilize the distorted triptycene structure.