Five-membered heterocycles benzene-fused

To confirm this finding based on the degree of the benzene ring C-C distortion, the magnetic susceptibility anisotropies and the relative energies for the benzene-fused five-membered heterocycles have been computed (Table 68). A similar approach was used by Schleyer et al. <1995AGE337> to evaluate the aromaticity of five-membered heterocycles using the ab initio methods. 

Some of the important benzene-fused five-membered heterocycles are indole, benzofuran, benzothiophene, benzimidazole, benzoxazole, and benzothiazole. The numbering of these heterocycles is shown below ... 

Due to the migration of C=C bond, the conjugated esters formed can accept the attack of a second nucleophile. Thus, by applying different difunctionalized benzenes, benzo-fused five-membered heterocyclic compounds 526 can be prepared... 

This approach was extended to evaluate the relative stability and reactivity of fused five-membered heterocycles and benzene, based on the computed physical properties of their ground states <1996JHC1079>. The computed structures are presented in Figure 33. 

As appropriately substituted o-disubstituted benzene derivatives are feadily available, this procedure has found widespread application in the synthesis of benzo-fused five-membered heterocycles. Examples abound in the various chapters in these volumes and the following few examples illustrate the general trend. 

Five-Membered Heterocycles Fused to One Benzene Ring... 

FIVE-MEMBERED HETEROCYCLES FUSED TO BENZENE intermediate 52 affords domperidone (66), a very... 

Cycloproparenes in which the benzene ring is fused to a five-membered heterocyclic moiety are accessible by the cycloaddition route from the appropriate dienes 188. Both the fiiran and thiophene derivatives 189 and 190 are isolable, but both are highly reactive. TTie difluoro derivative 191, prepared by an analogous route, has also been synthesized but decomposed rapidly in solution, while 192 was not isolable." ... 

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