Bridged Anulenes

On the basis of this definition (Fig. 1) the following classes of chiral compounds will be treated in this article cyclophanes, bridged anulenes and [8]anulenes, and ( )-cyclooctene and related structures. As mentioned above, metallocenes will be excluded. 

With regard to the stability of the skeletons of bridged anulenes, the possibility of a bridge inversion is of considerable interest. The availability of optically active bridged [10]- and [14]anulenes offered the chance to study these phenomena by race-mization experiments ... 

Fig. 1. Plane of Chirality Enantio-morphous figures and corresponding torsional angles A—X—Y—Z 7). Molecular examples ([n]paracyclophane, [2.2]meta-cyclophane, bridged[10]anulene and ( )-cyclooctene) with descriptors (/ , S)...

Bridged [10]- and [14]anulenes8 are of considerable interest not only because of their aromaticity (complying with HiickeFs rule) but also because of their (rigid) molecular geometry. The most simple representative l,6-methano[10]anulene (95) first obtained in 1964 U5), as well as others with oxido or imino bridges (cf. 103), have C2v-symmetry, but become chiral (C,) by substitution in any position. Such chiral anulenes can be classified as planar chiral under the assumption that the ten-... 

Apart from a footnote in a review article U8b) the first optically active bridged [10]-anulene was described in 1971 thus experimentally proving their chirality 119) The carboxylic acid 96 was resolved through i s salts with (+ )- and (—)-l-phenylethyl-amine ([a]D +250° in ethanol via the (—)-amine 117, U9)). The enantiomeric purity... 

Both the bisoxido- and bisimino-(cis)bridged dibromo[14]anulenes 115 and 116 with C2-symmetry could be quantitatively separated into their enantiomers by chromatography on triacetylcellulose in ethanol at 1.7 bar 124). The dextrorotatory enantiomers with [a]546 values of 1700° 115) and 1500° 116) in ethanol were eluted first. They exhibit very similar CD-curves with strong Cotton effects around 260... 

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