Setting the hook for specific single walled carbon nanotubes (SWCNT)

The electronic properties of SWCNTs depend strongly on well-defined characteristics such as their diameter, n,m-indices and chirality.[1–4] Traditional purification methods do not allow to selectively obtain samples of SWCNTs with precisely defined characteristics and high purity. The separation and purification of SWCNTs is an ongoing challenge as the selectivity towards traditional means of purification remains low at best. Here, we propose a new strategy to achieve a controlled and selective debundling and separation of SWCNTs depending on their size and chirality. The focus of this thesis is the design and synthesis of a molecular hook for specific SWCNTs. Conceptually, the hook consists of a chiral building block with a concave π-system, which can be accessed using stereospecific Diels-Alder reactions as key steps. Polymerization with interlinking building blocks then leads to chiral ribbons, which are envisaged to selectively coat a specific SWCNT and disperse it. The driving force for the coating process is mainly the interaction of the SWCNT with the concave π-moiety while the size exclusion is defined by the resulting secondary structure of the polymer, the polymer backbone and the interlinking molecules. Variation of the interlinking building blocks allows altering of the properties of the polymer at a late stage in the synthesis and ultimately defines the dispersion capability of the polymer. Each of the three successfully synthesized copolymers contains an enantiomerically pure ethenoanthracene derivative as the concave π-moiety. As a reliable release of the coated SWCNT is highly desirable, we further present a diamine monomer unit designed for Schiff base linked copolymerization that will allow for acid-labile depolymerization resulting in uncoating of the dispersed SWCNTs. Each of the polymer was characterized and the dispersion capability assessed subsequently

Bidentate Lewis Acid Catalyzed Domino Diels-Alder Reaction of Phthalazine for the Synthesis of Bridged Oligocyclic Tetrahydronaphthalenes

A domino process consisting of an inverse and a normal electron-demand Diels-Alder reaction is presented for the formation of bridged tri- and tetracyclic 1,2,3,4-tetrahydronaphthalenes catalyzed by a bidentate Lewis acid. The products were synthesized in a one-pot reaction from commercially available starting materials and contain up to six stereogenic centers. The tetrahydronaphthalenes were isolated as single diastereomers and are derivatives of phenylethylamine, which is well-known as a scaffold of amphetamine or dopamine

Bidentate Lewis Acid Catalyzed Inverse-Electron-Demand Diels-Alder Reaction for the Selective Functionalization of Aldehydes

The inverse-electron-demand Diels-Alder (IEDDA) reaction catalyzed by a bidentate Lewis acid was applied to enamines generated in situ from aldehydes. In general, a high functional group tolerance has been observed. Side reactions during the enamine forming step can limit the yield of the desired naphthalene. For citronellal as substrate, the initial intermediate after the catalyzed IEDDA reaction was trapped by an intramolecular Diels-Alder reaction to furnish a tricyclic compound. This scaffold represents the framework of natural products such as valerianoids A-C or the patchouli alcohol

Configurational Stability of [5]Helicenes

A series of [5]­helicenes difunctionalized in the fjord region with either fluoro, methoxy, or methyl groups was synthesized via photochemical and benzylic coupling route. Resolution of each compound into enantiomers and determination of the Gibbs activation energies of enantiomerization (Δ<i>G</i>^⧧(<i>T</i>)) revealed high configurational stability in all three cases. The Δ<i>G</i>^⧧(<i>T</i>) values of difunctionalized [5]­helicenes were compared with those of their monofunctionalized analogues and the parent [5]­helicene. Within this series, an exponential correlation between the torsional twist and Δ<i>G</i>^⧧(<i>T</i>) was found. The dimethyl derivative exhibits one of the highest configurational stabilities among [<i>n</i>]­helicenes reported to date, comparable to that of [9]­helicene