10-Te-4 Telluranes

Tellurachromones and telluraflavones readily convert to the cyclic 10-Te-4 telluranes 80 on reaction with bromine or peracetic acid (87JOC2123). 

By coupling with bromine under mild conditions 4-(4 -dimethylamino-phenyl)tellurapyrylium borotetrafluoride 25 affords 10-Te-4 tellurane 115 in 90-97% yield (86MI2). When bromine is taken in excess, an exchange of anions (BF Brj) in 115 takes place. The structure of the compound 115 (X = Brj) has been established by X-ray analysis. 

According to an X-ray study (86MI2) the halogen atoms (X = Br, Cl) in 10-Te-4 telluranes 120 take the axial positions in the trigonal-bipyramidal coordination polyhedron of the tellurium center. 

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