The results also revealed that ynamide 1l was reactive toward halocyclization, where excellent yields of both 2l and 3l were achieved when using 1 equiv. of each reagent. In contrast, the formation of the corresponding thiophenes was difficult, where 5l was afforded in an unsatisfactory yield due to the uncontrollable overiodination affording 5l'. Furthermore, bromothiophene 4l was not obtained when employing 2 equiv. of NBS, which led to the isolation of only 40% 2l along with a complex product mixture. This method is thus not suitable for substrates containing terminal alkynes such as 1m, 1n (see Supporting Information). A possible reaction mechanism for the halocyclization/oxidative aromatization was proposed (Scheme 2). The interaction between the electrophilic halogenating agent (NXS) and alkyne moiety in each substrate initiated the reaction. A critical consideration is the potential preference of the electrophilic halogenating agent for the thioester over the alkyne. The experimental results revealed that when NBS was mixed solely with the thioester 6, the reaction proceeded at a notably slow rate, leading to the formation of the disulfide and sulfenyl bromide. Notably, the bromocyclization reaction occurred efficiently when 1a was treated with NBS in the presence of 6 which did not change. Notably, 6 also did not change after a treatment with NIS alone. The deacetylation of intermediate A was facilitated by the succinimide anion or trace water in the reaction mixture. This step was confirmed by the detection of acetic acid and N-acetylsuccinimide (NAcS) in the NMR spectra of the reaction mixture in CD2Cl2 (Supporting Information). The mechanism of the subsequent oxidative aromatization was also assessed. The electrophilic halogenating agents, doubling as oxidants, targeted the 3position of dihydrothiophene B, thus leading to the formation of intermediate C. This was followed by two elimination processes to afford D and thiophene E. Notably, the treatment of 1k with NBS resulted in the formation of 2k', characterized as a gem-dibromide. The same reaction of 1j led to unclear results because of the complex mixture obtained. However, the NMR and mass spectra of the product mixture indicated the formation of gem-dibromides. Although caution should be exercised in overgeneralizing this mechanistic hypothesis, it is noteworthy that similar mechanisms have been proposed for other oxidative aromatization processes. However, it cannot be ruled out that the transient S-X bond formation was followed by the halogenation of the 3-position of B instead of a direct halogenation with NXS. Finally, we examined the further manipulated transformation of dihydrothiophenes to demonstrate the diverse applications of this method (Scheme 3). 3j, which could not be subjected to the one-pot aromatization with NIS, could be oxidized to produce thiophene 5j under conventional DDQ conditions. The Suzuki cross-coupling of 3a with boronic acid afforded 7 in an excellent yield. The MCPBA oxidation of 3a provided the dioxide 8, which was amenable to a further displacement reaction with pyrrolidine to produce 9. Notably, Flynn et al. conducted further manipulations of dihydrothiophenes 3e for biological studies. In conclusion, this study reported the one-pot halocyclization of alkynoic thioesters with N-halosuccinimide, followed by oxidative aromatization using the same reagent for the synthesis of thiophenes. The results revealed that the substituent on the terminal alkyne is crucial in terms of determining the substrate scope. The preliminary mechanistic studies indicated a halocylization pathway involving an interaction between the triple bond and electrophilic halogen, and a nucleophilic attack by the sulfur atom of the thioester. Currently, DFT studies are ongoing to investigate the mechanism in comparison with other alkenoic substrates. Further transformations of unsaturated thioesters, other than halocyclization, are also underway. Scheme 2. Proposed mechanism and mechanistic studies a NMR yield determined against 1,4-bis(trifluoromethyl)benzene as the internal standard.