Structure of [4.4]paracyclophane and three [m.n]paracyclophane derivatives

Abstract

The structures of the [2.3]paracyclophane

Paracyclophanes: Extending the Bridges. Synthesis

“…The structure determination of 43 (as well as its parent hydrocarbon [4.4]paracyclophane) by single-crystal X-ray structural analysis has already been reported by us earlier. [12] Table 1 shows that this is not true. C-i in [2.2]paracyclophane is deshielded (δ = 139.6 ppm) relative to C-i in [3.3]paracyclophane (δ = 138.4 ppm), yet C-iЈ (adjacent to the two-membered bridge, δ = 137.1 ppm) in [3.2]paracyclophane is shielded relative to C-i (adjacent to the three-membered bridge, δ = 139.6 ppm) in the same compound.…”

“…Among the ring contraction reactions the sulfone pyrolysis appeared most promising. Not only has this route been applied to the preparation of [3.3]-and [4.4]paracyclophane already, [12,[18][19][20][21] but its preparative variability (preparation of functionalized derivatives) and often good yield make it particularly attractive. [22] We hence decided to prepare [3.2]-(10), [4.2]- (14) and [4.3]paracyclophane (19) by this route.…”

“…Sulfone pyrolysis proceeded in very good yield again (68 %) and gave [4.2]paracyclophane (14), the structure of which was secured by comparing its spectroscopic data with those of the authentic material. [12] The last member of this series of unsubstituted hydrocarbons was [4.3]paracyclophane (19), synthesized from its constituting aromatic halves as described in Scheme 4. Scheme 4.…”

“…Now two Although these regioisomers could not be separated by chromatography, fractional crystallization allowed an enrichment of 29 to 96 %. Again the structure assignment of this compound rests largely on its NMR spectra (see below), but in this case an X-ray structural determination of the [3.2]cyclophane derivative 31 [12] resulting from it by sulfone pyrolysis via 32 made the structure proof unambiguous. Furthermore, since 31 could also be connected to 25a the assignments given for the phane derivatives in Scheme 5 rest on an even more solid basis.…”

“…[9] From m = 2 on all combinations are known, and many of them have been thoroughly studied from the structural, spectroscopic and chemical viewpoint, especially [2.2]- [4] and [3.3]paracyclophane. [4] For [4.4]paracyclophane [12] considerably less is known, and for those representatives with unequal molecular bridges - [3.2]-, [10] [4.2]-, [10] and [4.3]paracyclophane, [11] respectively -this is even more pronounced. We hence decided to develop efficient routes to these three hydrocarbons as well as several of their derivatives.…”