Diene-transmissive hetero-Diels-Alder

Furthermore, azo dienophiles have been employed in diene-transmissive hetero Diels-Alder reactions of cross-conjugated trienes which allow the straightforward construction of polycyclic compounds [297]. Theoretical interest has been directed to the hetero Diels-Alder reaction of diethyl azo di-carboxylate with 1,3-cyclohexadiene whose concerted course was demonstrated by means of a high pressure study [298]. 

Such syntheses take advantage of transannular intramolecular hetero Diels-Alder reactions [426], another impressive example is the diene transmissive hetero Diels-Alder reaction of the thioketone 5-14. The diene 5-15 formed by this cycloaddition underwent a second Diels-Alder reaction with N-phenyl-maleimide to yield the fused polycycle 5-16 as single diastereomer (Fig. 5-5) [427]. 

A diene-transmissive hetero-Diels-Alder reaction of cross-conjugated azatrienes provides a new, efficient, synthesis of ring-fused nitrogen heterocycles such as pyrimido-[5,4-c]pyridazin-6-ones 31 (Scheme 5) <97CC1013>. 

The Diene-Transmissive Hetero-Diels-Alder Reaction... 

Compounds with certain [3]heterodendralene structures including more complex substructures and substituents such as carbonyls, imines, and ylides are very popular, and hence many reports on their synthesis/generation, application and/or characterization, and so on, were found. However, only a few examples of their diene-transmissive hetero-Diels-Alder (DTHDA) reactions have been reported so far. For instance, although divinyl ketones ([3]-3-oxadendralenes, Scheme 2.1) are well recognized, for example, for their Nazarov cychzation [1] (see Chapter 3), only two reports are known on DTHDA reactions of p,p -diphenyl- and di-2-thienyl-substituted divinyl ketones vide infra) [8]. 

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