Functional carbo‐Butadienes: Nonaromatic Conjugation Effects through a 14‐Carbon, 24‐π‐Electron Backbone

Abstract

A systematic study of carbo-butadiene motifs not embedded in an aromatic carbo-benzene ring is described. Dibutatrienylacetylene (DBA) targets R(1) C(R)CCC(Ph)C≡CC(Ph)CCC(R)R(2) are devised, in which R is C≡CSiiPr3 and R(1) and R(2) are R, H, or 4-X-C6 H4 , with the latter including three known representatives (X: H, NMe2 , or NH2 ). The synthesis method is based on the SnCl2 -mediated reduction of pentaynediols prepared by early or late divergent strategies; the latter allows access to a OMe-NO2 push-pull diaryl-DBA. If R(1) and R(2) are H, an over-reduced dialkynylbutatriene (DAB) with two allenyl caps was isolated instead of the unsubstituted DBA. If R(1) =R(2) =R, the tetraalkynyl-DBA target was obtained, along with an over-reduced DBA product with a 12-membered 1,2-alkylidene-1H2 ,2H2 -carbo-cyclobutadiene ring. X-ray crystallography shows that all of the acyclic DBAs adopt a planar trans-transoid-trans configuration. The maximum UV/Vis absorption wavelength is found to vary consistently with the overall π-conjugation extent and, more intriguingly, with the π-donor character of the aryl X substituents, which varies consistently with the first (reversible) reduction potential and first (irreversible) oxidation peak, as determined by voltammetry.

Reductive Aromatization/Dearomatization and Elimination Reactions to Access Conjugated Polycyclic Hydrocarbons, Heteroacenes, and Cumulenes

“…In addition to optoelectronic characterization of the aryl cumulenes, they also conducted X‐ray diffraction analysis of the longest known cumulene 52 c . Other notable recent syntheses of cumulene‐containing molecules include the cumulene rotaxane 54 and the [3]cumulene 55 ,…”

π‐Conjugated Macrocycles Bearing Angle‐Strained Alkynes

“…[61][62][63] During the investigation of cumulenes ynthesis, Chauvin and co-workersf ound the interesting over-reduction of polyyne 243 afforded the angle-strained alkyne-containing macrocycle (Figure 73). [358] By controlling the tin-mediated reduction conditions and careful quenching with sodium hydroxide, cyclic dibutatrieneacetylene 245 was obtained in 16 %y ield together with linear butatrieneacetylene 244.T he strained structure of 245 was confirmed by X-ray crystallographic analysis (CCDC: 951899).…”

carbo‐Naphthalene: A Polycyclic carbo‐Benzenoid Fragment of α‐Graphyne

“…Tw oc arbo-benzene references are also described, C 18 Ar 6 and o-C 18 Ar 4 (CC-SiiPr 3 ) 2 .T he carbo-naphthalene bicycle is locally aromatic according to structural and magnetic criteria, as revealed by strong diatropic ring current effects on the deshielding of 1 Hn uclei of the Ar groups and on the negative value of the DFT-calculated NICS at the center of the C 18 rings (À12.8 ppm). [2, 3b, 7] Whereas acyclic and unicyclic molecular fragments of agraphyne have been exemplified by carbo-oligoacetylenes [8] and carbo-benzenes, [6,9] afirst fused bicyclicfragment is envisaged in a carbo-naphthalene.With av iew to securing both stability and solubility,t he selected target was octa(p-n-pentylphenyl)-carbo-naphthalene (1). [3] Besides putative variants (a-, b-, 6,6,12-graphynes), the existence of graphdiyne is today demonstrated, [4] and g-graphyne has been approached through several polycyclic molecular fragments.…”

“…[5] Them ost homogeneous variant is agraphyne (with only two types of CÀC bonds), that is,t he total carbo-mer of graphene ( Figure 1), [6] or al ayer of agraphityne. [2, 3b, 7] Whereas acyclic and unicyclic molecular fragments of agraphyne have been exemplified by carbo-oligoacetylenes [8] and carbo-benzenes, [6,9] afirst fused bicyclicfragment is envisaged in a carbo-naphthalene.…”