Synthesis and thermal cyclopolymerization of heterocycle containing bis-ortho-diynyl arenes K. Prasanna U. Perera, Mariusz Krawiec and Dennis W. Smith, Jr. * Department of Chemistry, Clemson University, Clemson, SC 29634, USA Received 30 April 2002; accepted 22 October 2002 Abstract—A new class of heteroatom terminated bis-ortho-diynyl arene (BODA) compounds have been synthesized via efficient in situ palladium catalyzed cross coupling between tetra alkynyl silanes and aryl bromides and iodides. BODA monomers undergo Bergman-type cyclization upon heating, and afford processable intermediates and ultimately network polymers. The new heterocycle terminated oligomers are compared to phenyl terminated derivatives and exhibit bathochromic shifts (25 nm) in their emission spectra. q 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction The Bergman cyclization 1–13 of enediynes has been used extensively as a viable methodology for developing antitumor drugs. 2 Recent work has shown that the cyclo- rearrangement of enediynes could also be used in preparing linear 3,4 and network polymers. 5–8 Although simple aryldiynes lead to linear polyarylenes which are difficult to process, we focused on the synthesis of bis-ortho- diynylarene (BODA) monomers (Scheme 1) which poly- merize to highly processable and reactive branched intermediates prior to final cure (Scheme 2). 5 Phenyl substituted BODA compounds were previously synthesized using a three-step synthetic protocol via selective ortho bromination of bisphenols followed by trifluoromethane sulfonato esterfication and subsequent Sonogashira 14 type Pd catalyzed coupling with mono- substituted terminal alkynes to form tetraynes. 5 Thermal polymerization typically above 2008C occurs in melt or in solution, yielding processable intermediates prior to the fully cured network polyarylenes with high thermal stability, low dielectric constant, and possibly electro- optic properties. In general, many high performance aromatic polymers are currently being pursued as low dielectric insulators in integrated circuits. 15,16 Most, however, do not exhibit adequate thermal and dimensional stability required for current fabrication processes. In our early communication we illustrate that phenyl terminated BODA polymers exhibit about 1%/1 h weight loss at 4508C. 5 BODA derived prepolymers can be easily coated or molded and are excellent precursors for microfabricated glassy carbon micro structures. 8 Recently, BODA derived polymers have been successfully used as precursors to fabricate carbon based photonic crystals. 9 BODA polymers may also be useful in the rapidly expanding area of organic light emitting diodes (OLED). 17 Our current effort has focused on developing a series of heteroaromatic ring terminated BODA monomers (Scheme 1) with hopes of enhancing the optoelectronic as well as the thermal properties of the final network. 2. Results and discussion Initially we attempted Sonogashira 14 type palladium coupling between aryl triflates and bromides with mono- substituted acetylenes as reported for other BODA mono- mers previously. 5 However, the instability of the related pyridyl and thienyl acetylene derivatives redirected our approach to in situ direct cross coupling reactions between alkynylsilanes and heteroaromatic bromides and iodides. The trimethylsilyl group has been extensively used as a protecting group for terminal acetylenes. 18 The C–Si bond of trimethylsilyl acetylene is typically cleaved by fluoride ions, tetrabutyl ammonium fluoride (TBAF), tetrabutyl- ammonium hydroxide (TBAOH) or silver (I) oxide. 19 Tour 20 and others 21 reported a base catalyzed (K 2 CO 3 ) desilylation in situ Pd-catalyzed coupling of an alkyne with an aryl halide to form oligo (1,4-phenylene ethynylene)s. Himaya 22 used F 2 to activate the Si – C bond enabling direct coupling of alkynylsilanes with aryl halides and Koseki et al. 23 reported the silver carbonate promoted direct cross 0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(02)01401-1 Tetrahedron 58 (2002) 10197–10203 * Corresponding author. Tel.: þ1-864-656-5020; fax: þ1-864-656-6613; e-mail: dwsmith@clemson.edu Keywords: Bergman cyclization; bis-ortho-diynyl arene (BODA); in situ palladium cross coupling.