Reversed-Polarity Synthesis of Diaryl Ketones through Palladium- Catalyzed Direct Arylation of 2-Aryl-1,3-dithianes

Reaction Scheme


The title reaction leads to satisfactory yields of dihydrodibenzoazepines�1?a�from norbornene. The dibenzoazepines�2�can also be accessed from compounds of type�1?b�when norbornadiene is used as a reactant. Theoretical studies show that the reaction represents a chelation-driven deviation from the usual selectivity observed in the presence of�ortho-substituents on the aryl iodide.



A Schlenk-type flask, equipped with a magnetic stirring bar, was charged under nitrogen with Cs2CO3 (326 mg, 1.0 mmol), PPh3 (14 mg, 0.055 mmol) and Pd(OAc)2 (5 mg, 0.022 mmol) in DMF (5 mL). After 10 minutes under stirring, a DMF solution (5 mL) of the aryl iodide (0.48 mmol), the 2-bromoaniline (0.44 mmol) and norbornadiene (97 mg, 1.05 mmol) was added. The resulting mixture was stirred in an oil bath at 105 �C for 24 h and then at 130 �C for additional 12� 14 h. After cooling to room temperature, the mixture was diluted with EtOAc (30 mL) and extracted three times with a saturated solution of NaCl (25 mL). The organic layer was dried over anhydrous Na2SO4, the solvent was removed under reduced pressure and the products were isolated by flash column chromatography on silica gel using mixtures of hexane-EtOAc as eluent.



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