Selenium- and Tellurium-containing Rings

In contrast to the less reactive l-(vinylthio)alkynes, their sulphoxides or sulphones reacted readily with Na Se to give 1,4-thiaselenins (212). Other studies dealt with the formation of 5,6-dihydro-2/f-selenop)rran, the synthesis of optically active 8-thia- and 8-selena-derivatives of l,r-binaphthyls, e.g. (213), and the formation of a tetracyclic selenium heterocycle on treatment of bicyclic selenoketals with Bu Li. A product that was obtained after oxidation of dimedone with SeOj has been identified as a tricyclic 1,3-oxaselenole. Selena- and 

Robert, L. Cazaux, C. Picard, and P. Tisnes, Tetrahedron Lett., 1980, 21,1039. 

Koeberg-Telder, F. Van de Griendt, and H. Cerfontain, J. Chem. Soc., Perkin Trans. 2, 1980, 

Laitalainen, T. Simonen, M. Klinga, and R. Kivekaes, Finn. Chem. Lett., 1979, 145 (Chem. Abstr., 

The thermolysis of 2,2-dimethyl-2,3-dihydrobenzo[6]selenophen oxide (215) proceeded by sy/i-elimination of selenoxide and intramolecular addition of the intermediate benzeneselenenic acid, Cleavage of 5-triselenan by its reaction with bromine offers a preparative pathway to bis-(bromomethyl) selenide. A series of naphthalene and tetracene dichalcogenides (216 X, Y = S, Se, or Te) were 

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Thiophen Rings Fused to other Heteroaromatic Systems that do not contain Sulphur, Selenium, or Tellurium.—Very many such annelated systems have been described, and in this section only those of particular note are mentioned. Annelation to other sulphur-, selenium-, and tellurium-containing rings is considered in a later section (p. 296). 

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