Radialenes synthesis

In contrast, the synthesis of tetraethynylethene (TEE, C10H4) was described in 1991 and, since then, a rich variety of cyclic and acyclic molecular scaffolds incorporating this carbon-rich molecule as a construction module have been prepared. The majority of these compounds, such as the expanded radialenes or the oligomers and polymers of the poly(triacetylene) type, are highly stable and... 

Since our earlier review1 appeared not so long ago, it makes no sense to repeat here all facets of the radialene family. Therefore, we focus here on the synthesis and chemical transformation of the radialenes, and we suggest the reader consult our earlier review for information on structural and spectroscopic data as well as the use of radialenes as building blocks for organic conductors and organic ferromagnets, as these topics will not... 

A variety of functionalized [3]radialenes have been prepared starting from the appropriately substituted cyclopropanes or cyclopropenes. West and Zecher have pioneered the chemistry of [3]radialenes with quinoid substituents. The general strategy of this synthesis is outlined in Scheme 513. A tris(4-hydroxyphenyl)cyclopropenylium... 

The condensation of hexachlorocyclopropane with three equivalents of the active methylene compound thioxanthene has been used for the synthesis of the electron-rich, blue [3]radialene 5327 (equation 1). 

The cyclodimerization of 82 to 83 is an example of a Ni(0)-mediated synthesis of [4]radialenes from [n]cumulenes. Applications of this method to butatriene derivatives 9050,63, 9164 and 9365,66 are shown in Scheme 10. The usefulness of Ni(0) catalysis for this transformation was first demonstrated by West and coworkers63 and later explored in detail by Iyoda and coworkers42,54,67. In some cases, Ni(0) catalysis improves the... 

The Ni(0)-mediated synthesis of [4]radialenes from hexapentaenes has also been investigated42 54 67. The regioselectivity of the cyclodimerization and the question of... 

When the organocuprate methodology is applied to l,l-dibromo-2-methylprop-l-ene, octamethyl[4]radialene (94) and decamethyl[5]radialene are the major products73. While this method does not offer any advantage over the Ni(0)-mediated syntheses of 94 (see above), it constitutes the only known synthesis of the permethylated [5]radialene (see Section II.C). For the sake of completeness, we mention that the Ni(0)-mediated dehy-drohalogenation/cyclotetramerization of 1,1-dibromoalkenes is not an efficient route to [4]radialenes66. 

Surprisingly little is known about isomerization reactions of [4]radialenes. 5,6,7,8-Tetravinyl[4]radialene 127 is certainly a unique case since it appears to be in equilibrium with its precursors in synthesis, 125 and 126, by electrocyclic reactions (equation 8). As 127 has not been isolated in pure form and is unstable with respect to polymerization, no details on this possible equilibrium are known79. 

The present volume deals with the properties of dienes, described in chapters on theory, structural chemistry, conformations, thermochemistry and acidity and in chapters dealing with UV and Raman spectra, with electronic effects and the chemistry of radical cations and cations derived from them. The synthesis of dienes and polyenes, and various reactions that they undergo with radicals, with oxidants, under electrochemical conditions, and their use in synthetic photochemistry are among the topics discussed. Systems such as radialenes, or the reactions of dienes under pressure, comprise special topics of these functional groups. 

Cyclodimerization of unsymmetrically substituted butatricncs such as 12 give both head-to-head and hcad-to-tail cycloaddition products. The structure of the head-to-head dimer was confirmed by its independent synthesis from the mixed cycloaddition of cumulenes 8 and 10,21 22 These dimerizations proceed by discrete nickel cyclopentanes which was established by the isolation of the 2-bispyridinenickel complex of the l.l,4,4-tetramelhylbuta-l,2,3-triene dimer.23 4-Radialenes with extended conjugation, potential organic conductors and semiconductors, have been prepared by similar methods as illustrated by the examples below.24,25... 

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