Synthesis and Supramolecular Properties of Trimethylene‐Bridged Clips

Abstract

The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers.

Living Radical Polymerization of Bicyclic Dienes: Synthesis of Thermally Cross-Linkable Block Copolymers

“…Monomers 2 and 3 were also prepared according to the literature procedures in multigram quantities. 34,35 Radical Polymerization. Emulsion polymerization of 1, carried out by Wood et al in 1960, 33 was reported to proceed exclusively via 1,4-addition, as characterized by infrared spectroscopy.…”

Effect of Substituents on the Complexation of Aromatic and Quinoid Substrates with Molecular Tweezers and Clips

“…The only product isolated from the high-pressure reaction, in 66% yield, was the desired (2:1) DielsϪAlder adduct 7d, which could be converted into 1d by DDQ dehydrogenation in 14% yield. As a precursor to the naphthalene-spaced tweezers 2iϪn, the bis-dienophile 5i was prepared by enolization of the known diketone 18 [7,22,32] with DBU and subsequent nucleophilic substitution of ethyl bromoacetate with the resulting enolate (85% yield) (Scheme 6). A DielsϪAlder reaction between 5i and the diene 6a and subsequent DDQ oxidation of the resulting bis-adduct 8i gave the tweezer 2i.…”

Synthesis and Self‐Aggregation of Enantiopure and Racemic Molecular Tweezers Based on the Bicyclo[3.3.1]nonane Framework

“…Molecular tweezers can in principle be divided into three groups: semirigid, [6][7][8][9][10][11][12][13] conformationally labile, [2,[14][15][16][17][18][19][20] and conformationally controlled by hydrogen bonds or metal chelation. [21][22][23] The interaction that mediates the recognition process can, in addition to London dispersion forces, be based on hydrogen-bonding, [24] charge-transfer, [14] ion-p, [8,25] p-p, [1] electrostatic, [8] and coupled interactions. [26] Most common are molecular tweezers with high symmetry, but there are some chiral examples.…”