Non-etching Preparation and Stereoselective Semi-hydrogenation of Potassium Trifluoropropynyltrifluoroborate for Vinylogous Trifluoromethylation
Reported herein is a Z- and E-selective vinylogous trifluoromethylation via Suzuki coupling using the corresponding potassium trifluoromethylvinyltrifluoroborates. The large-scale preparation of the precursor of these trifluoromethylvinyl fragments, trifluoropropynylBF 3K, is described from BF3·OEt2 and trifluoropropynyllithium (generated from an inexpensive commodity chemical, HFC-245a), without using hydrofluoric acid. Time-dependent semi-hydrogenation of the alkyne using poisoned palladium catalysts to provide either Z- or E-CF 3-vinyltrifluoroborate and coupling to prepare Z- and E-β-trifluoromethyl styrenes in good yields and isomeric selectivity has been described. A facile protocol of the preparation of potassium organotrifluoroborates under non-etching conditions is also achieved.
Ramachandran, Purdue University.
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