| Research Abstract |
Current interest has been concentrated on the chalcogen atom-containing reactive species generated by the fragmentation of cyclic chalcogenoacetals. However, few studies on the oxidation of cyclic polyaminopolychalcogenoacetals have been achieved in spite of the expectation to give various chalcogen-containing heterocycles through the oxidative ring contraction. Especially, it was expected that oxidation of conformationally flexible eight membered aminochalcogenoacetals would cause spontaneous transannular Ch-Ch interaction to give 1,5,3,7-dichalcogenadiazabicyclo[3.3.0]octane-type dichalcogena dications which would undergo further fragmentation to give novel cyclic dichalcogenidesby the attack of nucleophiles toward the methylene carbons of the dications, In this paper, we would like to describe a novelring contraction of 3,7-Disubstituted 2 H,6H-tetrahydro-1,5,3,7-dichalcogenadiazocines to 1,2,4-dichalcogenazolidines by treating with various oxidizing agents.
Treatment of 3,7-disubstituted 2 H,6H-tetrahydro-1,5,3,7-dithiadiazocines with bromine afforded 6H-dihydro-1,2,3,4,5,7-pentathiazocines in moderate yield and the addition of elemental sulfur in this reaction systems resulted in an increase of the yields of pentathiazocines. Reaction with sulfur chloride resulted in a good yield.
On the other hand, treatment of diselenadiazocines and ditelluradiazocines with various oxidizing agents afforded the corresponding 3H-dihydro-1,2,4-chalcogenazolidines in good yields. The intermediates of the reactions were supposed to be diselena or ditellura dications possessing 1,5,3,7-dichalcogenadiazabicyclo[3.3.0]octane skeleton generatedtransiently by the transannular interaction of two chalcogen atoms.
In conclusion, 2H,6H-tetrahydro-1,5,3,7-dichalcogenadiazocines subjected to selective ring contraction by treating with various oxidizing agents gave 1,2,3,4,5,7-pentathiazocines and 1,2,4-diselena- or ditellurazolidines, respectively.
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