Hexakis 3 radialene

The latter two molecules are, however, special cases, where forces other than those inherent in the [6]radialene system are determining the preferred conformation. Hexakis(ethylidene)cyclohexane is the only radialene molecule where structure results obtained in the solid state181, as well as in the gas phase182, are available for comparison (Table 21). 

C—C—C—C dihedral angle in gaseous hexakis(ethylidene)cyclohexane is 12.5° larger than the corresponding angle calculated for the parent radialene (6). This seems reasonable when the increased nonbonded repulsion due to the methyl substituents in the former is taken into account. 

In addition to calixarenes which have been made water-soluble as new inverse phase-transfer catalysts [85], novel ligands have been designed, based on a cydo-propene moiety bearing pyridyl substituents and called [hexakis(2- or 3-pyridyl) 3 -radialene] 37. A metallosupramolecular chemistry is envisioned by the authors and the solubility in water and their stability offer innovative perspectives [86]. 

In contrast to the parent [6]radialene, alkyl-substituted derivatives 113 and 115 are quite stable compounds that can even be handled in the presence of oxygen. All-( )-7,8,9,10,ll,12-hexamethyl[6]radialene (113) was the first radialene ever reported. It was obtained by dehalogenation of hexakis(l-chloroethyl)- [la] or hexakis(l-bromoethyl)benzene [lb] (112) with magnesium in methanol (Scheme 4.23). A recent GC/MS study of the product mixture has revealed the concomitant formation of several diastereoisomers of 113, which, however, could not be... 

Similarly, tetrathio-functionalized 2,3-dibromobutadienes 104, which also serve as precursors to [4]- and [5]radialenes (see Schemes 4.15 and 4.22), can be converted into hexakis(l,3-dithiol-2-ylidene)cyclohexanes 116a,b when treated with Ni(PPh3)4 and Zn-Cu couple in DMF (Scheme 4.24) [90]. Interestingly, these highly substituted [6]radialenes are initially formed with a twist-boat conformation of the central six-membered ring, which can be converted thermally into the more stable chair conformation (see below). 

Ito and coworkers have designed an electrochemical route to the elusive hexaanionlc-extended radialene 146 (Scheme 4.32), which was presumably formed in a six-electron reduction of hexakis(6-azulenylethynyl)benzene (145). 

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