Ir-Catalyzed Asymmetric Allylic Dearomatization Reactions

Dearomatization reactions provide the most direct synthesis of spiro- or fused-ring systems starting from readily available aromatics. The combination of dearomatization reaction with asymmetric synthesis would lead to the enantioselective construction of carbocycles and heterocycles, which are the frameworks for natural products and biologically active compounds. To date, the reported methods mainly focused on the stepwise protocol including dearomatization process and a subsequent asymmetric reaction. The direct asymmetric dearomatization reaction where the dearomatization and asymmetric catalysis occur in one step is highly desirable but very challenging.

In 2010, the researchers from the State Kay Laboratory of Organometallic Chemistry discovered that an iridium complex could catalyze the asymmetric allylic dearomatization of indoles. With [Ir(cod)Cl]2/phosphoramidite ligand L1, intramolecular C-3 allylic alkylation of indoles has been realized to afford highly enantioenriched spiroindolenine derivatives in excellent yields, drs and ees (Q.-F. Wu, H. He, W.-B. Liu, S.-L. You, J. Am. Chem. Soc. 2010, 132, 11418-11419.). The first iridium-catalyzed asymmetric allylic dearomatization reaction features ready availability of starting materials and a straightforward route to enantioenriched spiroindolenine derivatives.

Phenols are also cheap and abundant chemicals widely used in organic synthesis. Transition-metal-catalyzed allylic alkylation reactions of phenols generally proceeded as O-allylation with limited examples of C-allylation. Recently, the asymmetric allylic dearomatization reaction of phenols was also realized. The enantiopure spirocyclohexadienones obtained here could undergo diverse transformations, and may serve as versatile synthons in organic synthesis (Q.-F. Wu, W.-B. Liu, C.-X. Zhuo, Z.-Q. Rong, K.-Y. Ye, S.-L. You, Angew. Chem. Int. Ed.2011, 50, 4455-4458.).

This project was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology (973 Program), and the Chinese Academy of Sciences.

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