To get further insight into the reaction, control experiments were examined (Scheme 3). As mentioned above, S-Meprotected substrate 5 could not be used for the reaction. Electrooxidation of 5 did not give the desired compound 2a and brominated mono-cyclized product 6 was obtained in 19% yield (Scheme 3A). We also tried the reaction of the substrate protected by p-methoxybenzyl (PMB) groups, but 2a was not observed and mono-cyclized product 8 was obtained as a major product. To explain the reactivities, we carried out cyclic voltammetry of 1a, 5, and 6. Interestingly, the onset values of the oxidation potentials of 1a, 5, and 7 were similar (0.97, 1.00, and 0.93 V vs. Fc/Fc + , respectively), which were much more positive than that of Bu4NBr (0.21 V). These results cannot explain why only MOM-protection is effective, but suggest that Br -would be oxidized first on the anode in each case. We assumed that elimination of a MOM group would be faster than that of a Me group, and an eliminated PMB group would disturb the desired cyclization.