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

Abstract

Aring carbo-mer of naphthalene,C 32 Ar 8 (Ar = p-npentylphenyl), has been obtained as as table blue chromophore,a fter a1 9-step synthetic route involving methods inspired from those used in the synthesis of carbo-benzenes, or specifically devised for the present target, like ad ouble Sonogashira-type coupling reaction. The last step is aS nCl 2 / HCl-mediated reduction of ad ecaoxy-carbo-decalin, whichi s prepared through successive [8+ +10] macrocyclization steps. 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). The stability and aromaticity of this smallest fused molecular fragment of a-graphyne allows prediction of the same properties for the carbon allotrope itself.Inthe chemical design of two-dimensional carbon networks, [1] expanded graphenes containing both sp 2 -a nd sphybridized carbon atoms,t ermed "graphynes", [2] remain essentially investigated at the theoretical level. [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.With av iew to securing both stability and solubility,t he selected target was octa(p-n-pentylphenyl)-carbo-naphthalene (1). Consideration of classical methods used for the synthesis of carbo-benzenes from hexaoxy-[6]pericyclynes [10] suggests that 1 could be generated from decaoxy-[4,4,0]peribicyclynes,o rcarbo-decalins,s uch as 2 (Scheme 1). [11] Thel atter was thus regarded as an ultimate C 32 cycloadduct of ad inucleophile Nn with ad ielectrophile Em for m = 32Àn. While tentative routes for n = 14 proved unsuccessful (see the Supporting Information), for n = 22, the use of N12 (3a,b)and E10 (4)insuccessive [8+ +10] cyclization steps turned out to be productive via the intermediate pericyclyne N22 (14).Thep entayne 3b (R' = iPr) was obtained through ap rocedure previously implemented for 3a (R' = Et), [9b] via intermediates I and II, [12] and III-VI as described in the Supporting Information. Thed iketone 4 was targeted from the triyne 5,w hich was prepared following procedures described for Ar = Ph via intermediates VII-XI,w hich are also described in the Supporting Information. [10b] Conversion Figure 1. Progressive carbo-merization of graphene and its smallest fused fragment. Isolated carbo-meric Clar sextetsa re denoted ...

Steric/π‐Electronic Insulation of the carbo‐Benzene Ring: Dramatic Effects of tert‐Butyl versus Phenyl Crowns on Geometric, Chromophoric, Redox, and Magnetic Properties

“…As an alternative dielectrophile, the diketone 23 was prepared in one step through pseudo‐Sonogashira coupling of 13 with benzoyl chloride, by using a procedure previously implemented with an arylated triyne (R 2 =4‐ n Pent‐C 6 H 4 in Scheme ), to give 23 in 54 % yield (Scheme ). The structure of meso ‐ 23 was confirmed by XRD analysis of single crystals, which spontaneously resolved from a solution of the diastereoisomeric mixture (Figure S.3.1 in the Supporting Information)…”

A difluorenyl-carbo-cyclohexadiene: prospective chromophore for two-photon absorption

“…Using the Z-scan technique, a 2PA cross section 2PA = 656 GM was indeed measured for the carbo-benzene 1b upon femtosecond excitation at 800 nm ( Figure 1). More recently, preliminary Z-scan measurements performed on the carbo-quinoid 2 [11] indicated that the non-aromatic C18 core at stake tends to provide higher 2PA than the aromatic carbo-benzene version (2PA = 765 GM at 800 nm) [12]. As both the carbo-quinoid and carbobenzene cores possess two parallel C8 πconjugating paths, results suggested the design of carbo-chromophores with a single C8 conjugating path in a rigid planar environment.…”