Benzo thiophene derivatives reaction with acetylenes

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. " ... 

A useful reaction for the synthesis of unsaturated seven-membered heterocycles is the (2 + 2)-cycloaddition of heteroaromatic compounds, e.g., 1 //-pyrrole, furan, or thiophene derivatives, with acetylenes. In combination with a subsequent intramolecular (2 + 2)-cycloreversion (Section IV,B,2) of the annulated cyclobutene moiety, ring enlargement with two carbon atoms can be achieved. 1-Heterocycloheptatrienes, such as benzol6]azepines,26,27,65,66 benzo[fc]oxepins,67,68 benzo[6]-thiepins,69,70 and thiepins,18,71 have been successfully prepared in this way other routes are either nonexistent or laborious.72 In these compounds the reacting carbon-carbon double bond constitutes part of a (4n + 2)7r-electron system and in the (2 + 2)-cycloaddition the resonance energy of the aromatic nucleus is lost. Just like the nonaromatic heterocycles, heteroaromatic compounds have been reported to undergo (2 + 2)-cycloaddition reactions both with electron-deficient and with electron-rich acetylenes. 

Brooke GM, Quasem MA (1973) Partially fluorinated heterocyclic compounds. Part XI. The reactions of lithium pentafluorobenzenethiolate with acetylenic compounds giving benzo[fe] thiophen derivatives and/or olefins. 1 Chem Soc Perkin Trans 1 429-432... 

Several papers deal with the chemistry of benzo-2i/-thiopyrans of general type (69). The photoaddition reaction between thiobenzophenone and methoxyallene gives a mixture of a thietan derivative and the thiopyran (70), which rapidly isomerizes at 140 C to the 2/f-thiopyran (71). In a similar way, acetylenes add to thiobenzophenone to give products formulated as (72 R = Ph, CO2H, or CHaOH). Enamines of type (73) are converted thermally into benzo[c]thiophens (isothionaphthenes) (74), which form adducts with A -phenylmaleimide. ... 

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