Case Study 1: Photosensitized Auxiliary C(sp 3 )-H Fluorinations With standard conditions, substrate 4-phenylbutyl 4-fluorobenzoate (1a) provided 67% product yield (Table , entry 1). With the addition of 2.0 eq. of H-TEDA(BF 4 ) 2 to the reaction mixture, an 85% yield of 2a was obtained after the same time period (Table , entry 2). Although the presence of the 4-fluorobenzoyl auxiliary itself promotes the reaction by changing the aggregation state of SF ® , 10 it was clear to us that H-TEDA(BF 4 ) 2 further promoted this reaction.