Rh(I)–Diene-Catalyzed Addition of (Hetero)aryl Functionality to 1,3-Dienylsulfonyl Fluorides Achieving Exclusive Regioselectivity and High Enantioselectivity: Generality and Mechanism

Exclusively regioselective addition of (hetero)­aromatic groups to 1,3-dienylsulfonyl fluorides using the Rh­(I)/diene catalyst produces a class of (E)-2-aryl-4-(aryl or alkyl)­but-3-ene-1-sulfonyl fluorides in high isolated yields (up to 96%) across a broad substrate scope (44 examples) indicative of high functional group tolerance. A typical dienesulfonyl fluoride showed higher activity than an analogous dienone. DFT calculations (IEFPCM/PBE0/DGDZVP level of theory) on the selectivity-determining step are in full agreement (including accurate quantification of regioisomer ratios within the computational error) with the enhanced activity and selectivity of the dienesulfonyl fluorides. The origin of this enhancement was elucidated by QTAIM to most likely arise from higher electrostatic stabilization for the more polarizable dienesulfonyl fluoride due to the significant ionic character of the Rh-Cα/Cγ bond in the immediate nonconjugated 1,4-arylation product. The use of a C1-symmetric bicyclo[2.2.2]­octa-2,5-diene carrying a bulky 2,6-dimethylphenyl ester residue resulted in moderate to good yields (32–64%) together with up to 98% ee for both d-aryl- and alkyl-substituted buta-1,3-diene sulfonyl fluorides.