Cyclophane dianion

NMR spectra of syn and anti [2.2](2,7)fluorenophane dianions did not show a significant change as compared with fluorene anion itself194 . Indacene cyclophane dianions were prepared by Hafner195). 

Annulene and dehydro[22]annulene are also diatropic. A dehydroben-zo[22]annulene has been prepared that has eight C=C units, is planar and possesses a weak induced ring current. In the latter compound there are 13 outer protons at 6.25-8.45 8 and 7 inner protons at 0.70-3.45 5. Some aromatic bridged [22]annu-lenes are also known. The [26]annulene has not yet been prepared, but several dehydro[26]annulenes are aromatic.Furthermore, the dianion of 1,3,7,9,13,15, 19,21-octadehydro[24]annulene is another 26-electron system that is aromatic. Ojima and co-workers prepared bridged dehydro derivatives of [26], [30], and [34]annulenes. All of these are diatropic. The same workers prepared a bridged tetradehydro[38]annulene, which showed no ring current. On the other hand, the dianion of the cyclophane 89 also has 38 perimeter electrons, and this species is diatropic. ... 

In contrast to the conformationally mobile dianthrylethanes, the rigid cyclophane [11], with a face-to-face arrangement of the rc-layers, is electrostatically less favourable for reduction and only gives rise to a dianion upon alkali-metal reduction (Huber et al., 1983). 

The simplest polycycles stem from two triply-bridged points. These systems are exemplified by Trost et al. s 4,8-dihydrodibenzo[oi,g7z]pentalene (69) [87, 88], a precursor for a purturbed [12]annulene dianion, and Mislow et al. s double-bridged biphenyl derivatives (generally shown as 70) [89], where X is methylene, carbonyl, or various heteroatoms. Other longer bridged biphenyls include the triple-bridged cyclophanes 71 made by Hubert and Dale [90], their unsym-metrical relatives by Cram and Reeves [91], and the recent polyalkynyl cyclo-phane (72) made by Rubin et al. [92], a proposed fullerene precursor. 

The first alkali metal reduction study of cyclophanes was conducted by Mullen, who reduced 21 with Li [99]. Two anions were observed in the NMR spectra a dianion and a tetraanion. The chemical shifts of both these anions showed that a peripheral conjugation is present. The reduction drastically slowed down the rotation... 

Another approach to the synthesis of m- and p-cyclophanes is the reaction of m- andp-dibromobenzene with appropriate dianions, although in low yields." -" ... 

Phosphole tetramer 193, obtained by the pyrolysis of 1-phenyl-3,4-dimethyl-phosphole, incorporates two 2,2 -biphospholyl units linked by two P-P bonds. The P-P bonds could be reductively cleaved to form dianions containing one or two (194) 2,2 -biphospholyl units. Alkylation of those dianions with dihaloalkanes lead to the cyclophanes 195-197 (Scheme 12.67) [166]. 

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