Aryl derivatives heterocyclic synthesis, intramolecular

An interesting new application of enaminone chemistry is ring closure involving benzyne intermediates. In this way an intramolecular arylation of enaminones is effected. The method is used for the synthesis of fused heterocyclic compounds and natural products119-121. Phenanthridone derivatives can be obtained in good yield119. 

Like carbanions and anions from aryl amines, the anions from phenols have been used in intramolecular to obtain heterocycles by C—C bond formation [87]. One example of this approach is the photostimulated reaction of the phenoxide ion linked with a pendant bromoarene by Al-substi-tuted tetrahydroisoquinoline bridge such as 122. Under this reaction condition, aporphine alkaloid derivatives 123a,b (n=1) were obtained in good yields (Eq. 10.42). This approach was extended for the first time to the synthesis of a homoaporphine alkaloid 123c (w=2) [88]. 

The use of 1,2-dihaloarenes has been a key component of several recent annulation reactions that afford nitrogen heterocycles [274—276]. For example, indoles were prepared via a tandem amination/Heck reaction sequence between allylic amines and o-bromoiodobenzene derivatives (Eq. 48) [277]. A synthesis of heterocycles bearing three or more nitrogen atoms has been developed that proceeds via intermo-lecular A-arylation of a 3-aminopyridazine followed by intramolecular A-arylation of the resulting product (Eq. 49) [278]. This latter strategy has also been apphed to the constmction of other nitrogen-containing heterocycles [279]. 

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