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A novel methodology to accelerate annulation reactions leading to condensed selenium heterocycles was developed. The reactions of selenium dihalides with methyleugenol, allyl thymyl ether, allyl 1-naphthyl and 1-naphthyl propargyl ethers were carried out in the presence of alcohols, which considerably accelerated the annulation reactions. In solvent systems CH2Cl2/MeOH or CHCl3/MeOH, the reactions proceeded as annulation–methoxylation affording condensed methoxylated heterocycles. In the presence of isopropanol, the reactions were not accompanied by alkoxylation giving condensed halogen-containing products. The annulation reaction of selenium dihalides with 1-naphthyl propargyl ether included stereoselective anti-addition to the triple bond. The efficient selective synthesis of the first representatives of novel families of condensed selenium heterocycles with promising biological activity was developed. [ABSTRACT FROM AUTHOR]

The transannular addition of SeCl2 and SeBr2 to cis,cis-cycloocta-1,5-diene affords 2,6-dihalo-9-selenabicyclo[3.3.1]nonanes in high yields. The latter react with SeCl2 and SeBr2 to form the 2 : 1 complexes, which are the first representatives of coordination compounds with the Se…Se…Se bonds. X-ray crystallographic data of the obtained compounds are discussed. In contrast to 2,6-dihalo-9-selenabicyclo[3.3.1]nonanes, tetrahydroselenophene does not form complexes with SeCl2 and SeBr2 giving 1,1-dihalotetrahydroselenophenes. [ABSTRACT FROM AUTHOR]