The reaction proceeded only under irradiation conditions (Figure ), suggesting that the reaction did not occur by a radical chain mechanism. Furthermore, the quantum yield of the reaction irradiated with 450 nm blue LED (Φ = 0.57%) also supported the nonradical chain mechanism (Figure ). According to Table , entry 8, HE was not a suitable radical precursor, and use of the benzothiazoline skeleton was crucial to attaining excellent enantioselectivity. 15c In addition, dibenzyl, a radical dimer, was not detected under the reaction conditions. Thus, the results suggest that the free benzyl radical was not generated but direct radical transfer from the cation radical of benzothiazoline occurred in the transition state.