Amine‐Catalyzed Copper‐Mediated C−H Sulfonylation of Benzaldehydes via a Transient Imine Directing Group

Transient directing groups (TDGs) can provide a powerful means for C−H functionalization without requiring additional steps for directing group introduction and removal. We report the first use of a TDG in combination with copper to effect C−H functionalization. The regioselective copper mediated β−C(sp(2))−H sulfonylation of aldehydes with sulfinate salts is accomplished using catalytic β‐alanine to form a transient imine. A broad range of sulfonylated benzaldehydes are prepared using copper fluoride as both copper source and oxidant, involving a [5,6] cupracyclic intermediate. γ‐(peri)‐Sulfonylation of napthyl and phenanthrenyl carboxaldehydes is achieved through [6,6] cupracyclic intermediates. Further derivatisation of the aldehyde products is demonstrated. Kinetic experiments and Hammett analysis suggest the turnover limiting step to be a concerted asynchronous C−H cleavage via a dearomative Wheland‐type transition state.