Rosettes building blocks

FIGURE 4.2. Formation of the double rosette assemblies l3 (DEB)6, from its building blocks calix[4]arene dimelamine 1 and DEB. 

The multicomponent nature of hydrogen-bonded nanostructures based on rosette motifs as well as the multiple sites available for further chemical modifications at building blocks make these structures a very interesting candidates for the precise spatial arrangement of functional diversity onto solid supports. 

It was demonstrated that hydrogen bonded hexamers ( rosettes ) can be formed not only in the crystalline state but also in apolar solvents and that various well-defined self-assembled species can be obtained from building blocks in which melamine and barbiturate/cyanurate fragments are covalently attached in an appropriate way to a molecular skeleton.279... 

Scheme 3 presents substrates which carry both electron-donating and electron-withdrawing substituents. These systems, in comparison with the previous set of substrates, were considerably less reactive so that longer reaction times and excess oxidant were necessary for complete epoxidations. In the rosette are displayed the oxidation of p-oxo enol phosphates [13] 13, dihydrofuranone [17] 14, p-alkoxycyc-lohexenones [17] 15, alkoxymethylenecyclohexanones [17] 16, benzalphthalide [12a] 17, aurones [18] 18, flavones [19] 19, and isoflavones [18] 20. Many of these epoxides, which have become available for the first time, constitute valuable building blocks for natural product chemistry. 

Anionic Rosette Networks Assembled with Guanidinium and Ca-symmetric Oxo-anion Building Blocks... 

Anionic Rosette Layers Formed by Guanidinium and Non-Ca Molecular Building Blocks... 

Six merocyanine dyes (22) could be arranged together with three complementary cahxarene-based dimelamine chiral building blocks (23) in a chiral screw sense within a well-defined rosette supramolecular architecture (Fig. 17) [56]. A strong Cotton effect could be observed as a result of excitonic coupUng between the chromophores. 

Figure 3.20 Continued) (c) Formation of toroidal aggregates via assembly of barbituric acid/2,4,6-triamino-1,3,5-triazine building blocks. (Reproduced with permission from S. Yagai, S. Mahesh, Y. Kikkawa et aL, Toroidal nanoobjects from rosette assemblies of melamine-linked oligo(p-phenyleneethynylene)s and cyanurates., Angewandte Chemie International Edition, 2008, 47, 4691-4694. Wiley-VCH Verlag GmbH Co. KGaA.)...

Lam C-K, Xue F, Zhang J-P, Chen X-M, Mak TCW (2005) Hydrogen-bonded anionic rosette networks assembled with guanidinium and C3-symmetric oxoanion building blocks. J Am Chem Soc 127 11536... 

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