Cu‐Mediated Trifluoromethylation of Aromatic α‐Diazo Esters with the Yagupolskii–Umemoto Reagent

Reductive trifluoromethylation of aromatic α‐diazo esters at room temperature with the Yagupolskii–Umemoto reagent {[Ph 2 SCF 3 ][OTf]; ( 2a) } in DMF in the presence of excess CuCl gave a variety of α‐trifluoromethyl arylacetates in up to 93 % yield. The prior reaction of 2a with CuCl before the addition of the α‐diazo esters was imperative for the conversion. This initial reaction might pregenerate the key [Cu I CF 3 ] intermediate, according to the results of our control experiments. When the long‐chain perfluoroalkyl diphenylsulfonium triflates 2b – 2e were used instead of 2a , the reaction of an aromatic α‐diazo ester under the same conditions followed by treatment with NaHCO 3 gave a series of fluorinated α,β‐unsaturated esters in good yields. This protocol gives a facile, convenient, and practical access to α‐trifluoromethyl arylacetates and their analogues, implying that the “ + R fn ” reagents are compatible with α‐diazo esters in the presence of an appropriate reductant.