Synthesis of 1,3-diarylbenzo[c]selenophenes Arasambattu K. Mohanakrishnan * and P. Amaladass Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India Received 17 June 2005; revised 12 August 2005; accepted 17 August 2005 Available online 2 September 2005 Abstract—For the first time, syntheses of 1,3-diarylbenzo[c]selenophenes are reported involving a selenium transfer reaction of keto- alcohol/benzo[c]furan using Woollins reagent. Ó 2005 Elsevier Ltd. All rights reserved. Among the various linear conjugated systems devel- oped, poly(thiophene) derivatives have been paid much attention due to their electronic properties, stability and structural versatility. 1 The synthesis and character- ization of benzo[c]thiophene 1 analogs are well explored due to the low band gap properties associated with their polymer. 2 In particular, synthetic and electrochemical studies of 1,3-dithienylbenzo[c]thiophene 3 (Scheme 1) and its analogs have been well explored. 3 However, the preparation of benzo[c]selenophene 2 and its poly- mers has been explored only to a limited extent. Cava and co-workers reported the synthesis of 1,3-dic- yanobenzo[c]thiophene and 1,3-dicyanobenzo[c]selen- ophene analogs starting from o-xylene dicyanide using SOCl 2 and SeOCl 2 as sulfur and selenium transfer reagents, 4 respectively. They also reported the synthesis of 1,3-disubstituted benzo[c]selenophene analogs, 5 adopting the procedure established for naptho[c]thio- phenes. 6 Aqad et al. reported the synthesis and electro- chemical studies of seleno[3,4-b]quinoxalines. 7 The same group also reported 8 the synthesis of methylthio- capped bi-isothianaphthalene and bi-isoselenophene derivatives. The remarkably low band gap value of poly(benzo[c]thio- phene) prompted us to explore the synthesis of benzo[c]selenophene analogs. Since the synthesis of 1,3-dithienylbenzo[c]selenophene 4 (Scheme 1) is yet to be explored, we aimed at the preparation of 1,3-diaryl- benzo[c]selenophenes which could be reasonably stable. We have recently reported the synthesis of 1,3-diaryl- benzo[c]thiophenes, 9 including a general procedure from a variety of lactones 5, which were smoothly converted into the corresponding 1,3-diarylbenzo[c]thiophenes 7 via the intermediacy of the keto-alcohol 6 (Scheme 2). A survey of the literature revealed that Woollins reagent [PhP(Se)(l-Se)] 2 , a selenium analog of well-known sul- fur transfer Lawesson reagent, has been used for the preparation of selenoamides. 10 We envisioned that sele- nium transfer to keto-alcohol 6 followed by cyclization and dehydration similar to diarylbenzo[c]thiophene 9 would furnish 1,3-diarylbenzo[c]selenophenes. Contrary to the expectation, the reaction of keto alcohol 6a with 0.25 equiv of Woollins reagent at room temperature 0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2005.08.069 Keywords: Benzo[c]selenophene; 1,3-Diarylbenzo[c]selenophene; Woollins reagent. * Corresponding author. Tel.: +91 44 24451108; fax: +91 44 22352494; e-mail: mohan_67@hotmail.com S Se 1 2 3 4 S S S Se S S Scheme 1. O O Ar 1 S Ar 1 OH O Ar 2 Ar 1 Ar 2 5 6 7 Scheme 2. Tetrahedron Letters 46 (2005) 7201–7204 Tetrahedron Letters