Conjugated dienes interesting/important

Very interesting and potentially useful tandem processes shown in Scheme 34 [107-109] involve the conjugated diene cyclodimerization shown in Eq. 2 in Scheme 2 followed by trapping of the resultant 7r-allypalladium derivatives with an amine or alcohol. In this chapter, the vast and important... 

The catalysis of the stereospecific polymerization of conjugated dienes is of considerable interest from both the scientific and the industrial points of view [1,2]. From butadiene and isoprene, as the industrially most important 1,3-dienes, in comparison with the polymerization of olefins many more structurally different stereoregular polymers can be derived cf the structures of the stereoregular polybutadienes and polyisoprenes given in Scheme 1 [106]. 

Caution may be required in oxidation reactions. Ceric salts, for example, can alter or destroy products. Ferric salts seem to be more active in 1 N hydrochloric acid solution (P. Schudel, personal communication), but the acidic conditions may affect products such as enol ethers. Temperatures also seem to be important in some cases. For example, a substituted cyclohexa-diene complex was unaffected by CuClj at —20°, but it was converted into the free conjugated diene (mainly) at 0° and into the unconjugated diene and substituted benzene derivative at +20° (A. J. Birch and C. Sell, unpublished). In other cases, e.g., arylmanganese derivatives, although interesting synthetic reactions occur, the metal is not so readily removed. This general area is clearly one for further research if useful application is to be made in organic synthesis. 

An interesting 1,4-elimination reaction occurs upon treatment of allylic acetates with catalytic [Pd(Ph3P)4] together with propargylzinc bromide to act as a base (Scheme 43). What is important in this reaction is the observed regioselectivity, which is in contrast to that of previously reported palladium-catalysed elimination reactions giving conjugated dienes. 

The Diels-Alder cycloaddition is an important reaction class involving the reaction of unsaturated carbonyl compounds with conjugated dienes. The carbon atoms at the 1- and 4-positions of the conjugated diene system become attached to the doubly bonded carbons of the unsaturated carbonyl compound to form a ring stiucture. Diels-Alder chemistry is used in the synthesis of a variety of complex organic compounds of commercial interest, including insecticides, fragrances, plasticizers, and dyes (92). These bimolecular reactions have been used... 

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