Newman and co-workers have reported the hydrogenation of the C(sp 3 )-O bond at the homobenzylic position using hydrosilane and a Ni/ICy catalyst. They suggested direct cleavage of the C(sp 3 )-O bond by nickel hydride with the aid of the arene moiety as a directing group, although no mechanistic picture was provided. Thus, we decided to evaluate path B, even though direct substitution at CF3 is an uncommon event. A mechanistic study using a deuteriosilane agreed with path A. We tested the reaction of 2 with the deuteriosilane to clarify the hydrogen source (Scheme 3a). We observed deuterium incorporation not at the benzylic, but at the homobenzylic positions (88% D incorporation). Although this result agrees with path B, the possibility that the reaction could proceed via path A cannot be dismissed due to the possible existence of other proton sources for the benzylic position. We then conducted the reaction of 1a with the deuteriosilane (Scheme 3b). In this case, deuterated 2a and 3a were obtained in 20% and 50% yield, respectively. While the deuterium-incorporation rate at the benzylic position of 2a was high (89%), that of 3a was 50%. Taking into account the conclusion that 2a is a reaction intermediate of 3a, one benzylic deuterium atom of 2a would be converted to a hydrogen atom during the transformation of 2a into 3a. This would speak in favor of path A, in which a benzylic hydrogen is eliminated to form a difluoroalkene intermediate. The proton source would then most likely be water provided by hygroscopic potassium salts. In fact, when we performed the reaction of 2a in the presence of 1 equiv.