Diselenide-assisted sulfuration of dienes Andrzej Z. Rys, a Yihua Hou, a Imad A. Abu-Yousef b and David N. Harpp a, * a Department of Chemistry, McGill University, Montreal, Quebec, Canada H3A 2K6 b Department of Chemistry, American University of Sharjah, PO Box 26666, Sharjah, United Arab Emirates Received 21 September 2004; revised 15 October 2004; accepted 18 October 2004 Available online 2 November 2004 Abstract—Various diselenides assist in the sulfuration of dienes giving cyclic di- and tetrasulfides as main products. The reaction requires a 2-fold excess of diselenides to be efficient. Catalytic amounts of diselenides result in lower yields. This is likely due to secondary reactions (polymerization, aromatization) occurring during extended reaction times under catalytic conditions. It was verified that the sulfur-transferring properties of diselenatetrasulfides are virtually identical to those of diselenides combined with sulfur. Contrary to previous claims, not only the cyclic diselenatetrasulfide but also linear diselenatetrasulfides (RSeS n SeR) transfer sulfur to dienes. A mechanism is proposed and its implications to the nature of diatomic sulfur are discussed. Ó 2004 Elsevier Ltd. All rights reserved. Singlet diatomic sulfur is generally seen as a selectively reacting species converting dienes into disulfides in a Diels–Alder fashion. 1 One of the more interesting ways to transfer sulfur to dienes 1 was reported by Schmidt and Go ¨rl. 2 It involves use of a cyclic seven-membered ring 1,4-diselenatetrasulfide 2 as a 2-sulfur transfer rea- gent. Upon heating, heterocycle 2 contracts, releasing a two-sulfur unit (possibly 1 S 2 ) subsequently trapped by a diene 1 (R = alkyl, aryl) providing 3 accompanied by diselenide 4 (Eq. 1). Se Se 2 Se S S Se 1 R R + + R R S S 3 4 ð1Þ While the reaction was not particularly efficient and re- sulted in the formation of other products like thiophe- nes, for years it has been considered a model method for generating diatomic sulfur. 1 We were interested to extend the original Go ¨rl and Sch- midt method to linear diselenatetrasulfides. Although the authors commented on the linear 1,4-diselenatetra- sulfides as unsuitable for sulfur transfer purposes, no de- tails were provided. Recently, we have developed a simple and efficient meth- od to prepare both cyclic 2 and acyclic diselenatetrasul- fides, 5a–f from corresponding diselenides 4, 6a–f and trityl thiosulfenyl chloride Ph 3 CS 2 Cl (Eq. 2). 3 This easy access to such interesting compounds allowed us to study them as sulfur transfer reagents; we have examined this area and report our findings. In a compar- ative study, chlorobenzene solutions of 2,3-diphenylbuta- diene (1A) and various 1,4-diselenatetrasulfides 5 were refluxed under conditions similar to these reported by Schmidt (Eq. 3). To maximize the yields, a 2-fold excess diselenatetrasulfides 5 to diene was used instead of stoi- chiometric amounts; the results are presented in Table 1. Ph 3 CS 2 Cl R'SeS 2 SeR' R'SeSeR' 6a-f 5a-f a R' = Ph b R' = PhCH 2 c R' = O 2 NC 6 H 4 CH 2 d R' = MeOC 6 H 4 CH 2 e R' = MeOC 6 H 4 f R' = O 2 NC 6 H 4 ð2Þ The most striking observation was the significant formation of trapped products in the case of linear diselenatetrasulfides 5 (entries 1–3). Yields of cyclic disulfides exceeding 40% were typically observed and were higher than those obtained for cyclic diselenatetra- sulfide 2. 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.10.085 Keywords: Sulfur transfer reactions; Diselenatetrasulfides; Diatomic sulfur; Cyclic disulfides. * Corresponding author. Tel.: +1 514 398 6685; fax: +1 514 398 3797; e-mail: david.harpp@mcgill.ca Tetrahedron Letters 45 (2004) 9181–9184 Tetrahedron Letters