Heterocyclic compounds, aromatic benzofurans

Preparation of an appropriately disubstituted aromatic compound is the first step in the synthesis of fused aromatic heterocyclic compounds. Thus a method for the synthesis of benzofurans, coumarins etc. involves the preparation of the salicyl aldehydes as the first step. Standard methods are then used to add one or more carbon atoms and to effect cyclisation to complete the synthesis. 

The ASE values correlate with magnetic susceptibility for the five-membered heteroaromatic compounds. Magnetic and polarizability criteria put the order of aromaticity as thiophene > pyrrole > furan. The other criteria of aromaticity discussed in Section 8.2 are also applicable to heterocyclic compounds. HOMO-LUMO gaps and Fukui functions (see Topic 1.5) have been calculated for compounds such as indole, benzofuran, and benzothiophene and are in accord with the known reactivity patterns of these heterocycles. 

Benzo-annulated heterocyclic compounds such as oxindole and benzofuran derivatives were prepared in high yields by a novel cy-clization reaction of ethenetricarboxylate derivatives of aromatic compounds via Friedel-Crafts intramolecular Michael addition... 

V. Heterocyclic ring closure of o-hydroxylated aromatic compounds with acetylenic side chains. This method leads from acetylenic compounds 221 to 2-substituted benzofurans 222. Thus, l-(2-hydroxy-5-methyl)phenyl-2-phenylacetylene (221a), heated at 90° for 45 minutes in the presence of 2 iV NaOH, gives 5-methyl-2-phenylbenzofuran (222a) (90% yield). 

Richard, F, Drouillard, J., Carreyre, FI., Lemberton, J. L., and Perot, G. 1993. Zeolite catalyzed acylation of heterocyclic aromatic compounds. 1. Acylation of benzofuran. Stud. Surf. Sci. Catal. 78 601-606. 

Zeolite catalyzed acylation of heterocyclic aromatic compounds. I -Acylation of benzofuran. 

Like monoheteroatomic five-membered aromatic heterocycles with inbuilt 2,5 disposed electron-rich sites, indoles and benzofurans having 2,7 positions activated towards electrophiles such as carbonyl compounds, constitute precursors for performing direct syntheses of calix[/j]indoles and calix[ ]benzofurans. These hetero-cahxarenes provide aromatic 7t-electron-rich cavities. 

Coal tar is a complex mixture consisting almost exclusively of aromatic compounds. The main components of coal tar are naphthalene, phenanthrene, fluoranthene, pyrene, acenaphthene, anthracene, the heterocyclics carbazole, quinoline and isoquinoline, phenol and benzofuran-derivatives, as well as sulfur compounds such as thianaphthene. Olefinic compounds are also present in coal tar (Table 3.1). The total number of constituents is estimated at 10,000. 

The benzo-fiised counterparts of the simple heterocycles pyrrole, fiiran, and thiophene are indole, benzofuran, and benzothiophene. These compoimds are related to the two-ring, all-carbon aromatic compound naphthalene ... 

Horaguchi, T., Synthesis of benzofurans using photocychsation reactions of aromatic carbonyl compounds. Trends Heterocyclic Chem., 6, 1-19, 1997. 

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