Acetylenic Coupling: A Powerful Tool in Molecular Construction

Siemsen, Peter; Livingston, R. C.; Diederich, François

doi:10.1002/1521-3773(20000804)39:15<2632::aid-anie2632>3.0.co;2-f

Cited by 1,468 publications

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“…During the preparation of this paper [4], Tykwinski and co-workers [5] reported the synthesis of the related iso-PTAs 4a ± d but with peripheral Me groups and elongated acetylenic end groups. In addition to the structural differences, the two studies contrast in the synthetic strategy, with the formation of 3a ± d being based on sequential oxidative acetylenic coupling [6] and the preparation of 4a ± d taking advantage of Pd-catalyzed C(sp)ÀC(sp 2 ) cross-coupling [7] for the construction of the oligomeric backbone.…”

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confidence: 84%

Synthesis and Characterization of Multinanometer-Sized Expanded Dendralenes with an iso-Poly(triacetylene) Backbone

Burri¹,

Diederich²,

Nielsen

2002

HCA

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A series of [n]dendralenes (n 3, 4, 8, 3b ± d (Fig. 1)) expanded with buta-1,3-diynediyl moieties between the CC bonds were prepared by repetitive acetylenic scaffolding of 3-(cyclohexylidene)penta-1,4-diyne building blocks (Scheme). These remarkably unstable iso-poly(triacetylene) (iso-PTA) oligomers were characterized by 1 H-and 13 CÀNMR ( Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)-and C(sp 2 )-atoms in the backbone and represents the longest iso-PTA oligomer prepared to date. HOMO-LUMO Gap energies were determined as a function of oligomeric length ( Fig. 5 and Table 3), providing insight into the degree of p-electron delocalization in these cross-conjugated chromophores. A continous drop in the HOMO-LUMO gap with increasing number of monomeric repeating units provides evidence that cross-conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO-LUMO gap energy for an infinitely long, buta-1,3-diynediyl-expanded dendralene was extrapolated to about 3.3 ± 3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi-empirical calculations, revealing energetic preferences for planar or slightly twisted s-cis and −U-shaped× geometries.1. Introduction. ± Dendralenes are polyene hydrocarbons in which CC bonds are aligned in a cross-conjugated arrangement [1a]. This requires the presence of at least three CC bonds, and the simplest dendralene, therefore, is 3-(methylidene)penta-1,4-diene (a [3]dendralene). Novel synthetic approaches to dendralenes are currently being developed [1d,e], and these chromophores are increasingly investigated for their structural, electronic, and advanced materials properties [1]. Upon insertion of one or more acetylene units between the CC bonds, series of expanded dendralenes are obtained (Fig. 1). Diederich and co-workers [2] reported in 1995 the synthesis of the iso-poly(triacetylene)s 1a ± d by acetylenic scaffolding starting from appropriate tetraethynylethene (TEE, 3,hex-3-ene-1,5-diyne) precursors. Compounds 1c and 1d in this series are the first examples of expanded dendralenes, with buta-1,3-diynediyl bridges inserted between the CC bonds. More recently, Tykwinski and coworkers [3] introduced a new class of expanded dendralenes 2c ± i with the isopoly(diacetylene) backbone, featuring ethynediyl spacers between the CC bonds (the names iso-poly(diacetylene) (iso-PDA) and iso-poly(triacetylene) (iso-PTA) were introduced by Tykwinski and co-workers [3b]). In addition to compounds 2a ± i, with peripheral isopropylidene moieties, derivatives with peripheral cyclohexylidene and adamantylidene fragments were also reported [3d].

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Synthesis and Characterization of Multinanometer-Sized Expanded Dendralenes with an iso-Poly(triacetylene) Backbone

Burri¹,

Diederich²,

Nielsen

2002

HCA

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“…Whereas the first receptor in the series features a binding-cavity complementary in size to a monosaccharide, the three other macrocycles (for preliminary communications, see [15] [16]) provide larger recognition sites for the preferential accommodation of disaccharides. The assembly of these highly functionalized receptors elegantly takes advantage of oxidative acetylenic homo- [17] and Pd 0 -catalyzed arylÀalkyne cross-coupling [18]. We conclusively show that the strength of carbohydrate recognition becomes enhanced with an increasing number of bidentate ionic hostÀguest H-bonds, and that, with increasing number of these interactions, complexation in competitive protic solvent mixtures becomes more favorable.…”

Section: Synthetic Receptors For Monosaccharides and Disaccharides mentioning

confidence: 99%

Optically Active Cyclophane Receptors for Mono- and Disaccharides: The Role of Bidentate Ionic Hydrogen Bonding in Carbohydrate Recognition

Droz¹,

Neidlein²,

Anderson³

et al. 2001

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A new family of optically active cyclophane receptors for the complexation of mono-and disaccharides in competitive protic solvent mixtures is described. Macrocycles (À)-(R,R,R,R)-1 ± 4 feature preorganized binding cavities formed by four 1,1'-binaphthalene-2,2'-diyl phosphate moieties bridged in the 3,3'-positions by acetylenic or phenylacetylenic spacers. The four phosphodiester groups converge towards the binding cavity and provide efficient bidentate ionic H-bond acceptor sites (Fig. 2). Benzyloxy groups in the 7,7'-positions of the 1,1'-binaphthalene moieties ensure solubility of the nanometer-sized receptors and prevent undesirable aggregation. The construction of the macrocyclic framework of the four cyclophanes takes advantage of Pd 0 -catalyzed arylÐacetylene cross-coupling by the Sonogashira protocol, and oxidative acetylenic homo-coupling methodology (Schemes 2 and 8 ± 10). Several cleft-type receptors featuring one 1,1'-binaphthalene-2,2'-diyl phosphate moiety were also prepared (Schemes 1, 6, and 7). An undesired side reaction encountered during the synthesis of the target compounds was the formation of naptho[b]furan rings from 3-ethynylnaphthalene-2-ol derivatives, proceeding via 5-endo-dig cyclization (Schemes 3 ± 5). Computer-assisted molecular modeling indicated that the macrocycles prefer nonplanar puckered, cyclobutane-type conformations (Figs. 7 and 8). According to these calculations, receptor (À)-(R,R,R,R)-1 has, on average, a square binding site, which is complementary in size to one monosaccharide. The three other cyclophanes (À)-(R,R,R,R)-2 ± 4 feature, on average, wider rectangular cavities, providing a good fit to one disaccharide, while being too large for the complexation of one monosaccharide. This substrate selectivity was fully confirmed in 1 H-NMR binding titrations. The chiroptical properties of the cyclophanes and their nonmacrocyclic precursors were investigated by circular dichroism (CD) spectroscopy. The CD spectra of the acyclic precursors showed a large dependence from the number of 1,1'-binaphthalene moieties (Fig. 9), and those of the cyclophanes were remarkably influenced by the nature of the functional groups lining the macrocyclic cavity (Fig. 11). Profound differences were also observed between the CD spectra of linear and macrocyclic tetrakis(1,1'-binaphthalene) scaffolds, which feature very different molecular shapes (Fig. 10). In 1 H-NMR binding titrations with mono-and disaccharides (Fig. 13), concentration ranges were chosen to favor 1 : 1 hostÀguest binding. This stoichiometry was experimentally established by the curve-fitting analysis of the titration data and by Job plots. The titration data demonstrate conclusively that the strength of carbohydrate recognition is enhanced with an increasing number of bidentate ionic hostÀguest H-bonds (Table 1) in the complex formed. As a result of the formation of these highly stable H-bonds, carbohydrate complexation in competitive protic solvent mixtures becomes more favorable. Thus, cleft-type receptors (À)-(R)-7 and (À...

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“…For example, alkynyl/alkynyl couplings comprise the Eglinton, [67] Hay, [68] and Breslow [69] variants of the Glaser coupling reaction. [70] Synthesis efficiency has not been investigated in any systematic and comprehensive manner. The effect of the different reaction conditions on the efficiency of cycle formation is therefore difficult to predict, and has to be tested for each individual case.…”

Section: Introductionmentioning

confidence: 99%