Synthesis of a Macrocycle Bearing a Carbon Framework of [16]Cyclophenacene as a Carbon Nanobelt.

A synthetic pathway to a functionalized tetrahydro[5]phenacene was developed, which served as a precursor, leading to a dehydrobenzo[32]annulene macrocycle containing four carbon-carbon triple bonds. The high efficiency of the macrocyclization step can be attributed to the structural rigidity of its immediate precursor. Hydrogenation of the four carbon-carbon triple bonds produced a macrocycle bearing a carbon framework of [16]cyclophenacene as the shortest macrocyclic belt-like structure of an (8,8)armchair carbon nanotube.

Synthesis of Molecular Nanohoops Bearing a Tetrahydro[6]cycloparaphenylene Fused to a Hydrogenated or a Bithiophene-Inserted Cycloparaphenylene.

A synthetic pathway to a molecule bearing two molecular nanohoops, including a tetrahydro[6]cycloparaphenylene (4H[6]CPP) fused through two 1,4-dimethoxybenzene units to a 4H[10]CPP, was developed. Similarly, a molecule containing a 4H[6]CPP fused through two 1,4-dimethoxybenzene units to a molecular nanohoop bearing a [6]CPP inserted with two 2,2'-bithiophene-5,5'-diyl groups was synthesized. The Diels-Alder reactions of two (E,E)-1,4-diaryl-1,3-butadienes with 1,4-benzoquinone and the Ni-mediated homocoupling reactions are the key steps for the construction of macrocyclic ring structures. Oxidative aromatization with DDQ converted a hydrogenated system to a fully aromatized nanohoop with 10 aromatic units, including a [6]CPP inserted with two 2,2'-bithiophene-5,5'-diyl groups. The UV-vis and fluorescence spectra of the fused two-hoop systems were investigated.

Synthesis of a Cyclophane Bearing Two Benz[a]anthracene Units Connected at the 5 and 7 Positions with Two Naphth-1,4-diyl Groups.

A synthetic pathway to a cyclophane bearing two benz[a]anthracene units connected at the 5 and 7 positions through two naphth-1,4-diyl groups was developed, and its structure was confirmed by X-ray structure analysis. Because of structural constraints, the two naphthyl groups are distorted from planarity and the bonds connecting them to the benz[a]anthracene units are bent significantly. The UV-vis and fluorescence spectra of the cyclophane are red-shifted from those of 7-(1-naphthalenyl)benz[a]anthracene, which is the corresponding monomeric polycyclic aromatic hydrocarbon.

Synthesis and Characterization of Functionalized [12]Cycloparaphenylenes Containing Four Alternating Biphenyl and Naphthyl Units.

Functionalized [12]cycloparaphenylenes ([12]CPPs) containing four alternating biphenyl and naphthyl units were synthesized. A macrocyclic furan-containing CPP precursor was used for the Diels-Alder reaction with the parent benzyne or 3,6-dimethoxybenzyne to form the corresponding macrocyclic carbon frameworks. The subsequent reductive deoxygenation of the Diels-Alder adducts with Fe2(CO)9 followed by oxidative aromatization with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone produced the functionalized [12]CPPs. The effect of macrocyclic ring size on the reaction rate of oxidative aromatization was investigated.

Synthesis of Partially Hydrogenated Cycloparaphenylenes with Bent and Fused Structures Bearing Armchair Carbon Nanotube-like Connections.

The Diels-Alder reactions between 2 equiv of (E,E)-1,4-bis(4-bromophenyl)-1,3-butadiene and 1,4-benzoquinone led to the formation of a key intermediate with all four 4-bromophenyl substituents cis to one another. The subsequent nickel-mediated homocoupling reactions then produced partially hydrogenated cycloparaphenylenes, including a molecule bearing two units of tetrahydro[6]cycloparaphenylene (4H[6]CPP) fused together through two 1,4-dimethoxybenzene units in an armchair (6,6)carbon nanotube-like connection. Similarly, two 6H[9]CPPs were connected through three 1,4-dimethoxybenzene units in an armchair (9,9)carbon nanotube-like arrangement. A bent 8H[12]CPP and a bent 12H[18]CPP, which were fused intramolecularly with two and three 1,4-dimethoxybenzene units, respectively, to create the bent structures, were likewise synthesized. A molecule containing a bent 8H[12]CPP fused to a 4H[6]CPP was likewise constructed. The structures of these partially hydrogenated CPPs were established by X-ray structure analysis, NMR spectroscopy, and additional independent synthetic pathways.

Synthesis of Cycloparaphenylenes Bearing Furan-2,5-diyl or 2,2'-Bifuran-5,5'-diyl Units in the Macrocyclic Structures.

Synthetic pathways to furan-containing cycloparaphenylenes (CPPs) as molecular nanohoops bearing 10, 12, and 15 aromatic units including furan-2,5-diyl or 2,2'-bifuran-5,5'-diyl units have been developed. The X-ray structures of a partially hydrogenated bifuran-containing CPP precursor and the corresponding fully aromatized bifuran-containing CPP were obtained to allow the determination of their conformational arrangements in the crystal lattice. The optical and electrochemical properties of the furan-containing CPPs were investigated.

Twisted arenes.

The nonbonded steric interactions of substituents at the crowded C4 and C5 positions of phenanthrene cause the aromatic system to twist out of planarity. Similarly, the presence of substituents at the C1 and C12 positions of benzo[c]phenanthrene and at the C1 and C14 positions of dibenzo[c,g]phenanthrene are responsible for the helical twists of the aromatic frameworks. Highly substituted acenes, such as octamethylnaphthalene and decaphenylanthracene, also exhibit substantial end-to-end twists. The X-ray structures of these compounds allow direct measurements of the extent of the structural distortions. The configurational stabilities of many twisted arenes have also been determined.

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne-allenes.

5-(2-Methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene were synthesized by treatment of the corresponding benzannulated enediynes with potassium tert-butoxide in refluxing toluene to give benzannulated enyne-allenes for the subsequent Schmittel cascade cyclization reactions. The structures of these two 5-(1-naphthyl)-11H-benzo[b]fluorenes could be regarded as 2,2'-disubstituted 1,1'-binaphthyls with the newly constructed benzofluorenyl group serving as a naphthyl moiety.

Synthesis of a basket-shaped C56H38 hydrocarbon as a precursor toward an end-cap template for carbon [6,6]nanotubes.

A basket-shaped C(56)H(38) hydrocarbon (3) possessing a 30-carbon difluorenonaphthacenyl core that can be mapped onto the surface of C(78) was synthesized from 4-bromo-1-indanone. The first stage of the synthesis involved the preparation of tetraketone 10 as a key intermediate. The use of cascade cyclization reactions of benzannulated enyne-allenes as key features in the next stage of the synthetic sequence provides an efficient route to 3 from 4-bromo-1-indanone in 12 steps. The all-cis relationship among the methyl groups and the methine hydrogens causes the two benzofluorenyl units in 3 to be in an essentially perpendicular orientation to each other. Hydrocarbon 3 and its derivatives could serve as attractive precursors leading to a geodesic C(68)H(26) end-cap template for carbon [6,6]nanotubes.

Excited-state double proton transfer in model base pairs: the stepwise reaction on the heterodimer of 7-azaindole analogues.

A four fused-ring system 11-propyl-6H-indolo[2,3-b]quinoline (6 HIQ) is strategically designed and synthesized; it possesses a central moiety of 7-azaindole (7AI) and undergoes excited-state double proton transfer (ESDPT). Despite a barrierless type of ESDPT in the 6 HIQ dimer, femtosecond dynamics and a kinetic isotope effect provide indications for a stepwise ESDPT process in the 6 HIQ/7AI heterodimer, in which 6 HIQ (deuterated 6 HIQ) delivers the pyrrolyl proton (deuteron) to 7AI (deuterated 7AI) in less than 150 fs, forming an intermediate with a charge-transfer-like ion pair, followed by the transfer of a pyrrolyl proton (deuteron) from cation-like 7AI (deuterated 7AI) to the pyridinyl nitrogen of the anion-like 6 HIQ (deuterated 6 HIQ) in approximately 1.5+/-0.3 ps (3.5+/-0.3 ps). The barrier of second proton transfer is estimated to be 2.86 kcal mol(-1) for the 6 HIQ/7AI heterodimer.

Synthesis and structures of diindeno-fused 1,12-diphenylbenzo[c]phenanthrene and 1,14-diphenyl[5]helicene bearing severe helical twists.

Diindeno-fused 1,12-diphenylbenzo[c]phenanthrene 15 and 1,14-diphenyl[5]helicene 20 were prepared in a four-step synthetic sequence from 2,7-naphthalenedicarboxylic acid and 3,6-phenanthrenedicarboxylic acid, respectively. The X-ray structures of 15 and 20 show that the fused ring systems possess severe helical twists. The rotational barriers of the phenyl substituents were determined by the analysis of temperature-dependent 1H NMR spectra. [structure: see text]

Synthesis and Properties of Conjugated Macrocycles Containing 2,7-Bis(2-thienyl)-9H-fluoren-9-one Units.

Synthetic pathways to conjugated macrocycles containing one, two, or three 2,7-bis(2-thienyl)-9H-fluoren-9-one (TFOT) units in the macrocyclic frameworks bearing 10, 16, or 24 aromatic units were developed. The Diels-Alder reaction between (E,E)-1-(5-bromo-2-thienyl)-4-(5-iodo-2-thienyl)-1,3-butadiene and dimethyl acetylenedicarboxylate produced the key Diels-Alder adduct for the subsequent macrocyclic ring formation. UV-vis and fluorescence spectra of the TFOT-containing molecules were recorded, and their electrochemical properties were investigated by cyclic and differential pulse voltammetry. Solvatofluorochromic properties were observed for the TFOT-containing molecules.

Synthesis and Structure of a Functionalized [9]Cycloparaphenylene Bearing Three Indeno[2,1-a]fluorene-11,12-dione-2,9-diyl Units.

A synthetic pathway to a functionalized [9]cycloparaphenylene bearing three indeno[2,1-a]fluorene-11,12-dione-2,9-diyl units in the macrocyclic ring structure ([3]CIFO) has been developed. The 1H and 13C NMR spectra show that only the anti rotamer (anti-[3]CIFO) is produced. DFT calculations indicate that the anti rotamer is thermodynamically more stable than the syn rotamer by 4.3 kcal/mol, and the rotational barrier from the anti to syn rotamer is estimated to be 23.3 kcal/mol. The UV-vis and fluorescence spectra and cyclic voltammogram of anti-[3]CIFO were investigated.

Synthesis of the parent and substituted tetracyclic ABCD ring cores of camptothecins via 1-(3-aryl-2-propynyl)- 1,6-dihydro-6-oxo-2-pyridinecarbonitriles.

A new synthetic pathway to the parent and substituted ABCD ring cores of the camptothecin family of alkaloids was developed. The N-alkylation of 1,6-dihydro-6-oxo-2-pyridinecarbonitrile (2) with 3-bromo-1-phenylpropyne provided 3a using Curran's protocol. Treatment of 3a with a catalytic amount of DBU (5 mol %) at 110 degrees C for 12 h produced indolizino[1,2-b]quinolin-9(11H)-one (6a), the parent ABCD ring core of camptothecin, in essentially quantitative yield.

Synthesis of bowl-shaped polycyclic aromatic hydrocarbons via palladium-catalyzed intramolecular arylation reactions.

[reaction: see text] Treatment of the benzannulated enediyne 11 with potassium tert-butoxide in refluxing toluene for 12 h produced 15 via a cascade sequence of cyclization reactions. Two subsequent palladium-catalyzed intramolecular arylation reactions then afforded the bowl-shaped polycyclic aromatic hydrocarbon 16. The X-ray structures of 16 and two closely related molecules show the presence of significant curvatures.

Syntheses and Structures of Functionalized [9]Cycloparaphenylenes as Carbon Nanohoops Bearing Carbomethoxy and N-Phenylphthalimido Groups.

Functionalized [9]cycloparaphenylenes ([9]CPPs) bearing nine aromatic units in the macrocyclic structures were synthesized. The macrocyclic structures were substituted with carbomethoxy or N-phenylphthalimido groups. The Diels-Alder reaction of (E,E)-1,4-bis(4-bromophenyl)-1,3-butadiene or a related diene with dimethyl acetylenedicarboxylate followed by the nickel-mediated homocoupling reactions and oxidative aromatization produced the functionalized [9]CPPs. Treatment of a resultant [9]CPP with aniline or 1,4-diaminobenzene gave the corresponding N-phenylphthalimides. The X-ray structure of a [9]CPP bearing six carbomethoxy groups was obtained.

Syntheses and Structures of Thiophene-Containing Cycloparaphenylenes and Related Carbon Nanohoops.

Thiophene-containing cycloparaphenylenes (CPPs) bearing 8, 10, and 16 aromatic and heteroaromatic units in the macrocyclic ring structures were synthesized. Specifically, two and four thiophene-2,5-diyl units were incorporated into functionalized [6]- and [12]CPP macrocyclic carbon frameworks, respectively. In addition, two 2,2'-bithiophene-5,5'-diyl units were inserted into a functionalized [6]CPP carbon framework. The cyclic and differential pulse voltammetry and the UV-vis and fluorescence spectra of the fully aromatized macrocycles and their precursors exhibited interesting electrochemical and optical properties.

Determination of (4-methylcyclohexyl)methanol isomers by heated purge-and-trap GC/MS in water samples from the 2014 Elk River, West Virginia, chemical spill.

A heated purge-and-trap gas chromatography/mass spectrometry method was used to determine the cis- and trans-isomers of (4-methylcyclohexyl)methanol (4-MCHM), the reported major component of the Crude MCHM/Dowanol™ PPh glycol ether material spilled into the Elk River upriver from Charleston, West Virginia, on January 9, 2014. The trans-isomer eluted first and method detection limits were 0.16-µg L(-1)trans-, 0.28-µg L(-1)cis-, and 0.4-µg L(-1) Total (total response of isomers) 4-MCHM. Estimated concentrations in the spill source material were 491-g L(-1)trans- and 277-g L(-1)cis-4-MCHM, the sum constituting 84% of the source material assuming its density equaled 4-MCHM. Elk River samples collected⩽3.2 km downriver from the spill on January 15 had low (⩽2.9 µg L(-1) Total) 4-MCHM concentrations, whereas the isomers were not detected in samples collected 2 d earlier at the same sites. Similar 4-MCHM concentrations (range 4.2-5.5 µg L(-1) Total) occurred for samples of the Ohio River at Louisville, Kentucky, on January 17, ∼630 km downriver from the spill. Total 4-MCHM concentrations in Charleston, WV, office tap water decreased from 129 µg L(-1) on January 27 to 2.2 µg L(-1) on February 3, but remained detectable in tap samples through final collection on February 25 indicating some persistence of 4-MCHM within the water distribution system. One isomer of methyl 4-methylcyclohexanecarboxylate was detected in all Ohio River and tap water samples, and both isomers were detected in the source material spilled.

Biradicals/zwitterions from enallene-isonitriles. Formal [4 + 1] cycloadditions leading to 11H-indeno[1,2-b]quinoline and related compounds.

[reaction: see text] 1,3-Prototropic rearrangement of the benzannulated enyne-isonitriles to the corresponding enallene-isonitriles followed by cycloaromatization generated the putative quinoline biradicals/zwitterions. A subsequent intramolecular radical-radical coupling or electrophilic aromatic substitution then gave the formal [4 + 1] cycloaddition adducts leading to 11H-indeno[1,2-b]quinoline and related compounds.

Synthesis and structure of a helical diindenophenanthrene with four congested phenyl substituents as a molecular spiral staircase.

Treatment of 9 with potassium tert-butoxide produced 10 having a helical twist in a single operation. The X-ray structure of 10 shows that the four phenyl substituents are essentially parallel to one another but are virtually perpendicular to the helical axis of the diindenophenanthrene ring system. Viewing from the direction perpendicular to the helical axis, the structure of 10 resembles that of a segment of a spiral staircase having four parallel steps.