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Diorganyl Dichalcogenides-Promoted Nucleophilic Closure of 1,4-Diyn-3-ols: Synthesis of 2‑Benzoyl Chalcogenophenes

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journal contribution
posted on 2015-12-18, 00:00 authored by Juliano A. Roehrs, Renan P. Pistoia, Davi F. Back, Gilson Zeni
We report here the preparation of chalcogenophene derivatives via cyclization reactions of diynols promoted by diorganyl dichalcogenides and a halogen source. Different chalcogenophenes, such as 4-halo-selenophenes, 4-butylselenyl-selenophenes, halo-thiophenes, and 4-methylthio-thiophenes, were selectively prepared in good yields from the same starting materials. The results revealed that the halogen source had a significant effect on the proportion of 4-bromo-selenophenes and 4-butylselenyl-selenophenes. The best yields of 4-iodo-selenophenes were obtained with iodine as a halogen source, while the use of NBS gave exclusively the 4-butylselenyl-selenophenes. The experiments also revealed that the cyclization reaction to form 4-halo-thiophene derivatives can also be controlled changing the ratios of reagents. The 4-iodo-thiophenes were exclusively obtained by using dimethyl disulfide (2.0 equiv) and iodine (1.5 equiv), while the 4-bromo-thiophenes were obtained when the reaction was carried out with a 1.5 molar ratio of dimethyl disulfide and a halogen source. In addition, the reaction of diynols with an excess of dimethyl disulfide in the presence of NBS gave the 4-methylthio-thiophenes as sole products. We also studied the application of chalcogenophenes obtained as starting materials in the Suzuki, Sonogashira, and Ullmann cross-coupling reactions.

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