Cross-conjugated polyene

Poor correlations are obtained for cross-conjugated polyene systems such as... 

The simplest cross-conjugated polyene is 122, 3-methylene-1,4-pentadiene or 1,1-divinylethylene itself. Accepting the analysis in Reference 2 that was made using Roth s data, we find this species to be some 23 kJ mol 1 less stable than the simplest conjugated polyene, 80, (li)-, 3,5-hexatriene or 1,2-divinylethylene. The next simplest cross-conjugated polyenes are 3-methylene-l,4,6-heptatriene, 123, and 3,4-dimethylene-1,5-hexadiene, 124, that would naturally be compared with ( , )- ,3,5,7-octatetraene,... 

In spite of the continued interest in cross-conjugated polyenes ( dendralenes ), of which more than 100 are known307, surprisingly few of these have been investigated by PE or radical ion spectroscopy. ... 

By connecting double and single bonds, formally five classes of hydrocarbons can be constructed which differ considerably from one another not only chemically and physically but also in terms of their practical significance [1] the linear polyenes 1, the annulenes 2, which consist exclusively of endocyclic double bonds , the radialenes 3, polyolefins which are characterized by semicyclic double bonds, the fulvenes 4, hybrids containing endo-and semicyclic double bonds, and finally, the dendralenes 5 [2] which are acyclic cross-conjugated polyenes... 

Dendralenes [24] (acyclic cross-conjugated polyenes) have been used as dienes in tandem Diels-Alder reactions, and a methodology for the synthesis of highly functionalized angularly anel-lated aromatic compounds has been developed (Scheme 16.23) [25]. A tandem double Diels-Alder reaction of DMAD with [3]dendralene followed by oxidation with DDQ gave the tetramethyl ester... 

Dendralenes, acyclic cross-conjugated polyenes having a nonplanar structure, containing DT rings (DT[ ]dendralenes) have received considerable attention as novel multistage redox systems. The [3]- and [4]-dendralenes containing... 

For many, the true measure of DTDA sequences of cross-conjugated polyenes lies with their application in target-orientated synthesis. At present, only four examples have been reported in this area, each featuring a substituted [3]dendra-lene (or masked [3]dendralene) (Scheme 12.46). No doubt, as we advance our understanding and control of DTDA chemistry, many more examples will follow. 

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