Synthesis of helically chiral aromatics resulting from fusion of pyrene and [4]- or [5]helicene has been accomplished using photoredox catalysis employing a Cu-based sensitizer as the key step. Photocyclisation experiments for the synthesis of the target compounds were carried out in batch and using continuous flow strategies. The solid-state structures, UV/Vis absorption spectra and fluorescence spectra of the pyrene-helicene hybrids were investigated and compared to that of the parent [5]helicene to discern the effects of merging a pyrene moiety within a helicene skeleton. The studies demonstrated that pyrene-helicene hybrids adopt co-planar or stacked arrangements in the solid state, in contrast to the solid-state structure of the parent [5]helicene. The UV/Vis and fluorescence spectra of the pyrene-helicene hybrids exhibited strong red-shifts when compared to the parent [5]helicene. DFT calculations suggest that the strategy of extending the π surface in the y axis of the helicenes increased their HOMO levels while also decreasing their LUMO levels, resulting in significantly reduced band gaps.

[reaction: see text]. An efficient method for the in situ desilylation/oxidative dimerization of (trialkylsilyl)acetylenes is described. This protocol avoids the complications encountered with sensitive diynes by eliminating the deprotection and isolation steps. Various aromatic and alkyl diynes and tetraynes can be synthesized in a straightforward manner in good yields (82-99%) from TIPS-protected acetylenes. This method facilitates the efficient synthesis of novel tetrayne-bridged acetylenic cyclophanes 6 and 7 in a direct manner.

Four new classes of organic solvent soluble ethynylpentacene derivatives (2,9-, 2,10-, 2,6,9,13-, 2,6,10,13-) have been prepared by complementary, versatile, double Diels-Alder strategies. Functional groups on the A, C, and E rings can be manipulated to increase the solubility, modulate the electronics, and alter the solid-state packing. Cycloaddition reactions with diene 2 and 1,4,5,8-anthradiquinone (3) or ortho-quinodimethane 19 with 1-butyl-3-methylimidazolim iodide (18) as the iodide source (a significant improvement over NaI) and benzoquinone (20) followed by in situ aromatization afforded the quinones 4, 5, 21, and 22, respectively. For the 2,9- and 2,10- families, a one-pot desilylation/triflation was developed. Palladium(0) coupling and reductive aromatization afforded 2,9-di(triisopropylsilylethynyl)pentacene (10) and 2,10-di(triisopropylsilylethynyl)pentacene (11), respectively. Photodimerization of these pentacenes afforded the air-stable [4 + 4] cycloaddition pentacene precursors (tetrakisnaphthotricyclo[4.2.2.22,5]dodecanes, 12-15). Thermal cycloreversion of the dimers ( approximately 13 J/g, approximately 4 kcal/mol) produces the parent pentacenes (10 or 11). The tetrasubstituted family utilized a parallel route with extra versatility as the timing of the Grignard and palladium(0) coupling step may be varied depending upon the functional group combinations desired. The subsequent reactions provided the tetraethynylpentacenes 28-30, 33-35 (para-isomers), and 38 (meta-isomer). X-ray crystallography analysis of 28, 29, and 33 revealed various pi-pi stacked packing motifs that differ from the unfavorable herringbone pattern of pentacene.

[structure: see text] The syntheses of two distinct families of phenylyne helical cyclophanes with potential for organic materials are described. The meta-bonded atropisomers afford interesting bowtie-like and butterfly-like conformers from a palladium(0), copper-mediated coupling sequence. Molecular modeling revealed the contrasting stereochemistry in these systems from differential molecular folding pathways during cyclization. The interplanar separation of the superimposed aromatic rings is approximately 3.5 A.

Recently the synthesis and study of assorted carbocyclic cyclophanes and cage compounds [1] has been augmented by novel heterocyclic arrays. Representative examples include bis-2,2'-bipyridine units in twisted diyne dehydroannulenes for spectroscopic detection of metal ions, [2] butadiyne-bridged [4 4 ](2,6)pyridinophanes, [3] rigid cross-conjugated acetylenic macrocycles as a cyclic alternative for 4,4'-bipyridine functionalities for metal complexation, [4] and related thiophenebridged macrocycles. [5] Phenanthroline-based investigations involve studies of copper complex induced DNA cleavage, [6] the mechanism of strand scission, [7] enhancement of Diels±Alder reactions, [8] and applications of a cationic platinum±phenanthroline complex. [9] Substituted 1,10-phenanthrolines are highly fluorescent and the spectra are modulated by protonation or metalion complexation. [10] [2]Catenanes have been assembled by employing copper(i)±phenanthroline units, [11] and copper(i)± biphenanthrolines have provided scaffolds for molecular grids. [12] We report here the synthesis of the helical 1,10-phenanthroline-capped cyclophanes 1 ( Figure 1) and 11 (Scheme 2), which possess the potential for complexation with various metals, as illustrated by the insertion of copper(i) ions in 2 and 12. Bromosilylacetylene 3 was converted into its organozincate [1e±g, 13] by in situ halogen metal exchange with nBuLi, followed by transmetalation with ZnBr 2 (Scheme 1). Addition of [Pd(PPh 3 ) 4 ] and 3,8-dibromophenanthroline (4) [14] afforded 5 in 87 % yield when DMF was used as a co-solvent. [15] Suzuki couplings also provide 3,8-diaryl-1,10-phenanthrolines. [14c, 16] Deprotection of 5 with K 2 CO 3 in MeOH/THF provided 6 in 85 % yield.We anticipated that controlled addition of copper(ii) acetate to 6 (diethyl ether/pyridine) would initially generate the intermediate complex 7. This ™copper template∫ would then facilitate the desired coupling reaction and circumvent the competing formation of acetate 8 from direct coordination with Cu(OAc) 2 . [17] The geometric environment of intermediate 8 will inhibit the desired reaction relative to that of 7 in which the terminal acetylene groups are suitably disposed for intermolecular coupling. In addition, polymerization pathways often observed in similar dimerizations should be diminished. [18] Experimentally, addition of copper(ii) acetate (initially 0.5 equiv) in a mixture of pyridine/diethyl ether initiated the reaction and allowed for the formation of 7. Subsequent addition of excess reagent (5.5 equiv) completed the coupling and afforded the copper(i)-complexed cyclophane 2 in 84 % yield (Scheme 1). Supporting evidence for this mechanism was provided by the observed color changes from yellow (6) to red (7) to green after an excess of Cu(OAc) 2 was added. Further confirmation of the importance of the copper COMMUNICATIONS 4520