Intramolecular Reactions in Pseudo‐Geminally Substituted [2.2]Paracyclophanes

Abstract

A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11 a, and 11 b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11 b do not lead to a cyclobutadiene intermediate. In the latter case the "half-closed" butadiene derivative 17 was isolated. A Paterno-Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11 a, on treatment with n-butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11 b with iron pentacarbonyl.

[2.2]Paracyclophane‐Bis(triazole) Systems: Synthesis and Photochemical Behavior

“…Figure presents seven acetylene‐subtituted paracyclophanes, namely 4‐ethynyl[2.2]paracyclophane 1 , pseudo‐gem bis(ethynyl)[2.2]paracyclophane 2 , pseudo‐ortho bis(ethynyl)[2.2]paracyclophane 3 , pseudo‐meta bis(ethynyl)[2.2]paracyclophane 4 , pseudo‐para bis(ethynyl)[2.2]paracyclophane 5 , 4,5‐bis(ethynyl)‐[2.2]paracyclophane 6 , and the cross‐tetrasubstituted derivative 4,7,13,16‐tetraethynyl[2.2]paracyclophane 7 , which have all been prepared from the corresponding brominated and/or formylated derivatives . Since then, these compounds have been used in coupling reactions, addition reactions, and in the synthesis of polymers and luminescent compounds…”

π‐Stacked Oligo(phenylene vinylene)s Based on Pseudo‐Geminal Substituted [2.2]Paracyclophanes: Impact of Interchain Geometry and Interactions on the Electronic Properties

“…As a result, there are minimal interactions between the two conjugated segments as soon as their lengths are increased.The pseudo-geminal (pg) substitution pattern of [2.2]paracyclophane holds substituents on each ring directly atop one another. Such stacking of conjugated units leads to facile intramolecular photochemical cycloadditions, [4][5][6][7] and new electronic transitions in multi-decker stacks. [8] The opportunity to prepare new materials containing the cyclophane core has recently attracted increased attention.…”

“…[9,10] Here, we explore the absorption and fluorescence spectra of stacked PV oligomers that are based on the pg-CP core: the stacked stilbene pg-CP(PV 2 ) 2 and the analogoues distyrylbenzene, pg-CP(PV 3 ) 2 . We compare the spectroscopic and electronic properties of the pg compounds to those of their pp and po analogues and the corresponding isolated oligomers.Conjugated arms were installed on the pg core by a Heck reaction between 4,15-divinyl[2.2]paracyclophane [5] and 1iodobenzene or 1-iodo-4-styrylbenzene to afford pg-CP[PV 2 ] 2 and pg-CP[PV 3 ] 2…”

Selenium halide-induced bridge formation in [2.2]paracyclophanes

“…The ratio of 5 and 6 was determined as 1:1.4. It is interesting to note that the synthesis of the [2.3.2](1,2,4)cyclophane derivative 5 has been previously reported as the result of bromine addition to bis(acetylene) 1 , in 87% yield [13]. …”

“…Thus, unsaturated cyclophane bis(esters) undergo intramolecular photocyclization, yielding the corresponding ladderane isomers [9–11]. The ethynyl group is well known for its ability to undergo coupling reactions, making the pseudo-geminal bis(acetylene) 1 and its derivatives good candidates for building molecular scaffolding [12–13]. The reaction between bis(acetylene) 1 and other acetylene derivatives has been reported to provide new π-bridges in [2.2]paracyclophane [14].…”