Abstract
The syntheses of syn‐[2.n]metacyclophan‐1‐enes (n = 5, 6, 8) in good yields using the McMurry cyclization of 1,n‐bis(3‐formyl‐4‐methoxyphenyl)alkanes are reported. Conversion of syn‐[2.6]‐ and [2.8]metacyclophan‐1‐enes to the corresponding highly strained syn‐type [2.6]‐ and [2.8]metacyclophane‐1‐ynes was achieved by successive bromination and dehydrobromination reactions. An attempted trapping reaction of the putative corresponding [2.5]metacyclophane‐1‐yne by Diels–Alder reaction with 1,3‐diphenylisobenzofuran failed due to its smaller ring size and strained structure. X‐ray crystallographic analyses show that the triple bonds in syn‐[2.6]‐ and [2.8]metacyclophane‐1‐ynes are distorted from linearity with bond angles of 156.7° and 161.4°, respectively. A DFT (Density Functional Theory) computational study was conducted to determine the stabilities of different conformations of the target compounds.
Highlights
Cyclophanes are an important class of compounds that have been shown to possess unique properties
[2.n]metacyclophan-1-ones were obtained.5a,b Later, we reported the successful preparation of syn- and anti-[2.8]metacyclophan-1-enes using the low-valent titanium-induced McMurry coupling reaction and their conversion to syn- and anti-[2.8]metacyclophane-1-ynes, in a ratio of 35:65.6 The bromine adduct of [2.10]metacyclophan-1ene on the other hand, gave the [2.10]metacyclophane-1-yne as the major product, along with a monodehydrobrominated product 1-bromo[2.10]metacyclo-phan-1-ene as a by-product
In continuation of our previous work related to the synthesis of [2.n]metacyclophane-1-ynes,6 we report the first synthesis of highly strained
Summary
Cyclophanes are an important class of compounds that have been shown to possess unique properties. This has attracted the interest of many research groups. These properties include having highly strained and unusual conformers with distorted aromatic ring components and this has resulted in much ongoing research into the fundamental aspects of aromaticity.. The highly strained cyclophynes containing at least one ethyne bridging group have proven to be elusive. Was inferred by Psiorz and Hopf as the transient intermediate that led, via its cyclotrimerization reaction, to the formation of the novel C3-symmetrical hydrocarbon [a] [b] [c] [d] [e] [f] [g] [h].
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