Synthesis and characterisation of novel hexaalkoxytriphenylenes bearing an additional alkyl chain in the a-position Andrew N. Cammidge * , Hemant Gopee, Hitesh Patel School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7T, UK article info Article history: Received 12 January 2009 Revised 20 February 2009 Accepted 5 March 2009 Available online 16 March 2009 Keywords: Triphenylenes Discotic liquid crystals Alkylation abstract Exhaustive alkylation of hexahydroxytriphenylene results in production of significant quantities of a side product bearing one additional alkyl chain originating from C-alkylation. A series of these novel materials have been isolated and characterised to gain further insight on factors controlling mesophase formation in triphenylene discotics. Ó 2009 Elsevier Ltd. All rights reserved. Certain disc-like molecules (‘discotics’) can form liquid crystal phases. Most usually, the molecules assemble as columns to give so-called columnar mesophases (which can be likened to the smec- tic mesophases formed by rod-like/calamitic molecules) (Fig. 1). Substituted triphenylene derivatives which present a flat, aromatic core surrounded by flexible chains, are the most widely studied class of discotic liquid crystals. 1 In some cases a less ordered nema- tic phase is exhibited in which the molecules retain only orienta- tional order. Triphenylene discotics have received particular interest because of their ability to act as one-dimensional charge transport materials, acting as photoconductors or semiconductors on doping 2 and, alongside other discotic frameworks, lend them- selves to diverse electronic and optical applications. 3 Synthetic and applications science has advanced in parallel and a significant challenge has revolved around unravelling and under- standing the structural factors that control the formation of stable mesophases. Triphenylene has proved to be a versatile scaffold for such fundamental interrogation of structural factors controlling mesophase behaviour (stability, type, etc.). New and improved synthetic protocols have now led to characterisation of a wide range of symmetrical (most common) and unsymmetrically substi- tuted derivatives. 4 We have established a set of qualitative parameters governing mesophase formation and stability in triphenylene discotics and have argued that the central core of such discotic molecules ex- tends beyond the central aromatic triphenylene unit to include the attached conjugated substituents. 5,6 Perturbation of this ex- tended core has a dramatic effect on the mesophase behaviour. For example, hexaalkoxytriphenylenes (HATs) such as HAT6 are the most studied triphenylene-based discotic liquid crystals and are typically characterised as giving columnar hexagonal mesopha- ses (Fig. 1). 7 Replacement of one conjugating substituent with an- other tends to maintain the mesophase behaviour. 4d,7–9 However, exchange with, or addition of, a non-conjugating group tends to destroy the mesophase (Fig. 1). 4g,8,10–12 We recently reported the unexpected first examples of meso- phase-forming triphenylenes bearing a substituent linked to the core by a saturated methylene group. 13 These derivatives were formed as side products when attempts were made to introduce terminal alkene functionality on typical hexaalkoxytriphenyl- enes. Observation of mesophase behaviour was surprising but it was unclear if this series represented something of a special case or whether this general structural motif supports meso- phase stability. Consequently we decided to investigate the same structural motif within the series of parent alkoxy/alkyl triphenylenes. Unsymmetrically substituted triphenylenes such as 10–13 could conceivably be prepared selectively from appropriate ben- zene and biphenyl derivatives using precedented methodolgy. 12 However, our previous work has demonstrated that alkylation of hexahydroxytriphenylene produced the C-alkylated side prod- uct in some cases and we reasoned that using this route would be both convenient and allow us to investigate the reaction itself to gauge its significance in such triphenylene syntheses (Scheme 1). In a typical procedure therefore, hexahydroxytriphenylene 9 was reacted with an alkyl bromide (K 2 CO 3 /EtOH/reflux) for 24 h. 0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2009.03.089 * Corresponding author. Tel./fax: +44 (0)1603 592011. E-mail address: a.cammidge@uea.ac.uk (A.N. Cammidge). Tetrahedron Letters 50 (2009) 3513–3515 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet