4,5,12,13‐Tetrabromo[2.2]paracyclophane – A New Bis(aryne) Equivalent

Abstract

The reaction of 2 with nBuLi at -78°C generates aryne intermediates within the aromatic rings of [2.2]paracyclophane which are trapped in Diels-Alder reactions with dienes like furan, 1,9-diphenylisobenzofuran, or cyclopentadiene. Reductive deoxygenation with low-valent titanium reagents or oms cannot be removed anymore by reduction. TMSI converts the adducts of furan and isobenzofuran into

Intramolecular Electron Transfer between Terminal 1,4-Dimethoxybenzene Units in Radical Cations with a [2.2](1,4)Naphthalenophane, [2.2](1,4)Anthracenophane, and Pentacene Skeleton

“…Therefore, we tried to protect these positions by phenyl substitution. In analogy to the synthesis of 9,9Ј,10,10Ј-tetra- [11] , the aryne intermediates derived from 4,5,12,13-tetrabromo[2.2]paracyclophane (6) [12] were trapped by 4,7-diScheme 2 methoxy-1,3-diphenylisobenzofuran (7) [13] to give a mixture of the expected three diastereomeric bis-cycloadducts (overall yield 74%): syn,syn-8a, syn,anti-8b, and anti,anti-8c, which were separated by flash chromatography (Scheme 2). The stereochemical terms syn and anti refer to the orientation of the bicyclic oxygen bridge with regard to the [2.2]paracyclophane skeleton.…”

“…Preferentially formed is the anti, anti-8c (about 35%), whereas the syn,syn-8a is produced in only very low yield. Treatment of these isomers with trimethylsilyl iodide [11] [14] removes not only the bridging oxygen atoms, but also cleaves the methoxy groups. Therefore, we confined the further experimental studies to the anti,-anti-8c.…”

“…Their attempts to achieve a further cycloaddition were unsuccessful. Under enforced conditions (reaction temperature 200°C), however, it is possible to carry out a double cycloaddition to give the required 1,4,8,11-tetramethoxypentacene-6,13-dione (11), which was reduced by treatment with lithium aluminium hydride followed by trimethylsilane to afford 6,13-dihydro-1,4,8,11-tetramethoxypentacene (12). Preliminary dehydrogenation tests of 12 in solu- Scheme 3 tion showed that the generated violet 1,4,8,11-tetramethoxypentacene (5) decomposes rapidly.…”

“…[12] (457 mg, 0.87 mmol) and 4,7-dimethoxy-1,3-diphenylisobenzofuran [13] (573 mg, 1.74 mol) in anhydrous THF (50 ml) was added dropwise at Ϫ40°C a 0.32  butyllithium hexane solution (10 ml, 3.3 mmol) over a period of 30 min. After warming up to room temperature and addition of methanol (10 ml) and water (100 ml), the mixture was extracted with dichloromethane (2 ϫ 100 ml).…”

Carbon Rich Cyclophanes with Unusual Properties — an Update

“…The in situ-trapping of the corresponding bis-aryne with furan gave two isomeric cycloadducts (49), that could be reductively deoxygenated to anti- [2.2]naphthophane [36]. The aryne intermediate is trapped more efficiently with 2,5-diphenylisobenzofurane (45) and the deoxygenation with trimethylsilyl iodide (TMSI) yields the highly fluorescent anti-tetraphenyl [2.2]anthracenophane 46 [37]. By treatment of 44 with 1.0 equiv.…”