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.