To compare the obtained results with those of our recent study on alkenoic thioesters, we initially investigated employing an alkynoic thioester 1a and commercially available electrophilic halogenating agents (Table ). The treatment of thioester 1a with either Br2 or NBA, an optimal reagent for alkynoic thioesters, in dichloromethane at room temperature resulted in a complex product mixture containing bromothiophene 4a in a low yield (entries 1 and 2). Employing tetrabromocyclohexadiene (TBCHD) or 1,3-dibromo-5,5-dimethylhydrantoin (DBDMH) as brominating agents afforded the desired products in generally higher than moderate yields (entries 3 and 4). Notably, 1.0 equiv. of DBDMH was essential to afford the thiophene 4a in a good yield. On the other hand, we could not obtain the corresponding bromodihydrothiophene 2a in an acceptable yield with 0.5 equiv. of DBDMH (entry 5). Notably, the addition of 2 equiv. of N-bromosuccinimide (NBS) afforded 4a in an 82% yield (entry 6), while the addition of 1 equiv. afforded the bromodihydrothiophenes 2a and 4a in yields of 41% and 13%, respectively. Furthermore, 33% of 1a was recovered which can be attributed to the fast oxidative aromatization (entry 7). Employing 3 equiv. of NBS invoked the further bromination of 4a and afforded 3,5-dibromothiophene. The iodocyclization/oxidative aromatization of 1a using N-iodosuccinimide (NIS) was then investigated. The results revealed that employing an excessive amount of NIS without further iodination afforded 5a in an excellent yield (entry 8), thus indicating that the oxidative aromatization in this case was slower than that of 2a with NBS where the use of 1 equiv. led to a higher yield of iododihydrothiophene 3a rather than that of 2a (entries 7 and 9). Unfortunately, using 2-3 equiv. of NIS did not provide 4a in a satisfactory yield. Table . Optimizing the reaction conditions.