Conjugated polyalkenes

Table 3.4 Conjugated polyalkene substrates for the asymmetric dihydroxylation reaction. a b...

In the frame of the present project, a detailed analysis of known total rate constants koH for OH + alkene reactions was carried out, revealing that for monoalkenes and non-conjugated polyalkenes, the total rate constant can be expressed as a sum of independent, partial rate constants for addition to a given double-bonded C-atom. These site-specific Iq depend only on the stability type of the ensuing hydroxyalkyl radical, which can be either primary, secondary or tertiary. Thus, there are only three such ki, denoted here as prim scc and kf n [19]. It should be... 

The purpose of the doping agent is either to remove electrons from the tt system (p-doping or to add electrons to the TT system (n-doping). Ap-doped polyacetylene can be represented as a conjugated polyalkene... 

More than 100 years ago, Kekule recognized the possible existence of other-conjugated cyclic polyalkenes, which at least superficially would be expected to have properties like benzene. The most interesting of these are cyclobutadiene, 23, and cyclooctatetraene, 24 ... 

The conjugate addition of organocopper reagents to polyalkenic carbonyl compounds presents an opportunity in which either 1,4-, 1,6- and sometimes 1,8-addition can occur. Much of the early woik in this area was conducted in the study of the reaction of a dienoate or dienone with an alkylcuprate or a catalytic copper/organomagnesium combination. The predominant mode of addition for the reaction of a dienoate and a copper-based organomagnesium reagent was found to be 1,6 not 1,4.72 If the opportunity of 1,8-addition was present, then this mode prevailed.73 However, a truly systematic study has not been carried out with the various reagents. 

Compounds containing sulfur, nitrogen, and oxygen could possibly interfere with the performance of the test. Monoalkenes do not interfere, but conjugated di- and polyalkenes, if present, may interfere with the test performance. 

The bonding description for a coordinated alkene can be extended to other unsaturated organic ligands. Polyalkenes may be non-conjugated or conjugated. In complexes of non-conjugated systems (e.g. cycloocta-1,5-diene (cod), 23.20, or... 

Existing SARs for OH + polyalkene reactions merely attribute a reactivity to a specific complete C=C structure or to a complete C=C-C=C structure for conjugated dienes. These SARs provide no information with relevance to the detailed product distribution of the various possible OH-adducts. 

Figure 11.17. Examples of unsaturated fatty acids. Large numbers of such alkenes both as ( )- and (Z)-isomers exist. The intermediate in the oxidation of arachidonic acid to (only one shown member of the) prostaglandins is part of a cascade of reactions to an entire family of compounds that vary in oxidation state. Leukotrienes (three conjugated double bonds and no five-membered ring) and thromboxanes with six-membered oxygen-containing rings (oxa-cyclohexane, pyran, oxane) are also derived from C20 polyalkenes.

Polyalkenic conjugated hydrocarbons can be classified on the basis of the connectivity of their ethylene units. The linear polyenes 1 and annulenes 2 are comprised of vicinal linked units, whereas the dendralenes 3, and their cyclic counterparts the radialenes 4, contain geminal linkages (Figure 12.1). In addition to these four principal classes, hybrid molecules that exhibit both vicinal and geminal connectivity are possible, as illustrated by the fulvenes 5. 

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