Title: Benzo[1,2-b:4,3-b']dithiofeen en thieno[3,2-e]indolen als bouwstenen voor heterohelicenen.
Other Titles: Benzo[1,2-b:4,3-b']dithiophene and thieno[3,2-e]indoles as building blocks for heterohelicenes.
Authors: Nulens, Wienand; M0318157
Issue Date: 5-May-2009
Abstract: Helicenes are organic compounds consisting of a series of ortho-condense d aromatic rings which, due to increasing steric repulsion between the t erminal rings, adopt a helical conformation. Helicenes exhibit interesti ng non-linear optical properties due to their inteherently chiral conjug ation. Enantiomerically pure helicenes could also be used as ligands in asymmetric catalysis. In the first chapter, we investigated the synthesis of tetrathia[7]helic ene and a few derivatives functionalised with alkyl chains using well-kn own consecutive McMurry- and photocyclization reactions. Here, we manage d to obtain a small number of helicenes, but the yields were limited due to troublesome photocyclization reactions and the limited reactivity of the intermediary benzodithiophene derivatives. Despite these difficulti es, we were successful in measuring some of the optical properties of th ese compounds. The synthesis of 1,2-bis(thienyl)benzenes and their conve rsion into helicenes was hindered by similar problems. In the second chapter we inquired into some new, non-photochemical synth eses for substituted benzodithiophenes to allow for large-scale reaction s. Unfortunately, none of these reactions yielded good results. The synt hesis of 3,3’-bis-benzothiophenes and 3,3’-biindolyl compounds and their conversion into the corresponding [5]helicenes also gave insurmoun table difficulties. Using a more classical approach via the synthesis of 1,2-bis(benzothienyl)ethenes, these compounds, though easily accessible , could photochemically nor oxidatively be converted into helicenes. We were more successful with the synthesis of mixed aza-thia-[7]helicene s, based on the dimerization of substituted thieno[3,2-e]indoles. We dev eloped a new procedure for the synthesis of these thienoindoles, based o n the fluoride mediated indolisation of 5-amino-4-ethynylbenzothiophenes . Though a multi-step procedure, thienoindoles can be now be obtained st arting from 5-amino-benzothiophenes in high yields. The conversion of some of these thienoindoles into helicenes via a dimer isation-photocyclisation procedures yielded variable results. The main p roblem was the instability of the bis(thienoindolyl)ethenes during the f inal photocyclization step, limiting the yields of this reaction to a ma ximum of 20%. Despite this we managed to obtain a few new helicenes. Fur ther investigation into these new systems can certainly be recommended. A synthesis of 1,2-bis(indolyl)benzenes, which are structurally analogou s to the bis(thienyl)benzenes obtained in Chapter 1, failed. The fluorid e-mediated indolization, successful in the synthesis of thienoindoles, i n this case only led to the decomposition of the starting products. In the final chapter we did a preliminary study into the conversion of 3 -formylquinoline derivatives to diaza[5]helicenes. Here, we easily obtai ned a new [5]-helicene and, depending on the reaction conditions us ed, a diazabenzoperylene as a major side product. With this we created a basis for the synthesis of larger pyridohelicene derivatives.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Molecular Design and Synthesis

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