Further study revealed that the reaction was highly influenced by the amount of water in the system (Table ). In the presence of 5 equiv and 15 equiv of H2O, 2a was obtained in yields of 66% and 67%, respectively (entries 1 and 2). The yield of 2a significantly increased to 79% with 30 equiv of H2O (entry 3). With H2O (50 equiv), the yield of 2a was conversely decreased to 66% (entry 4). For efficient transformation, the amount of water was quite significant. The amount of n Bu4NBr can be reduced to a catalytic amount. With 0.5 equiv of n Bu4NBr, 2a was obtained in a similar yield, but the reproducibility of the reaction was slightly decreased (entry 3). With an appropriate amount of water, generation of 3a and 4b was suppressed even with 3 equiv of n Bu4NBr. In the presence of n Bu4NBr (3 equiv) and H2O (50 equiv), the desired product 2a was obtained in the highest yield among the reactions examined thus far (84% yield, entry 4). N.D. N.D.