Dewar benzo thiophene

Benzo[f]thiophene 710 is prepared by the dehydration of sulfoxide 709 with KOBu as a variant method of the Pummerer reaction. Irradiation of 710 affords 711 as a first example of Dewar benzo[dthiophene (Scheme 108) <1995TL3177>. Reaction of dinitrile 712 with thionyl chloride in the presence of EtsN yields thieno[3,4-dthio-phene 714 via Pummerer dehydration of the intermediate 713 <2000TL8843, 2002JOC2453>. 

The first Dewar benzo[f]thiophene 108 was obtained by irradiation of 4,5,7-tris(/r t/-butyl)benzo[f]thiophene 107with ultraviolet (UV) light (A > 340 nm) in trideuterioacetonitrile (Scheme 57) <1995TL3177>. This product is thermally surprisingly stable (Section 1.06.5.2) and no change was observed after heating a solution in acetonitrile at 100 °C for 40 h. 

Useful reviews on redox transformations of thiophen derivatives (179 references), on the stereochemistry of carbonyl derivatives of five-membered heterocycles (257 references), on synthetic approaches to dihydrothiophens (135 references), and on biosteric thiophens" have been published. Aspects of thiophen chemistry have been treated in reviews on the synthesis of heterocycles by thermal [2 + 2] cycloaddition reactions of acetylenes and on aspects and perspectives of organic heterocyclic chemistry. A review comparing the chemistry of thieno[2,3-h]- and thieno [3,2-i ]-thiophen with that of benzo[ft] thiophen and quinoline has been published. In Advances in Heterocyclic Chemistry, the development of benzo[6] thiophen from 1968 to 1980 and of selenophen from 1970 to 1980 was presented. Other aspects of thiophen chemistry are treated in chapters on Dewar Heterocycles," on Cyclizations under Vilsmeier Conditions, on Polyfluoroheteroaromatic Compounds, and on Reactions of Benzyne with Heterocyclic Compounds. " Several dissertations treating various aspects of thiophen chemistry have appeared. " ... 

ERE determinations of indole have given results ranging from 4 I S to 57.6 kcal mole-1.263 Dewar et aZ.10-12 have calculated Dewar resonance energies for various benzo-fused compounds and obtained the following orders of decreasing resonance energy benzo[6]thiophene, 24.8 kcal mole-1 indole, 23.8 kcal mole-1 benzo[6]furan, 20.3 kcal mole-1. However,... 

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