Tellurapyrylium salts

Reactions of l-telluracyclohexa-2,5-dienes 21 have been little studied. When heated with HPF6 in acetic acid, compounds 21 eliminate dihydrogen and convert to tellurapyrylium salts 25. The yields (73-83%) are higher than those of the same reaction with the oxygen, sulfur, and selenium analogs of 21 (88MI2). 

Treatment of heterocyclic ketones 22 with ethyl fluorosulfate leads to tellurapyrylium salts 25a (82JOC5235 87JOC2123), and interaction with Meldrum s acid produces compounds 29. 

The reactions of the dibenzo derivative of the tellurapyrylium cation, 10-telluroniaanthracene, were studied in considerable detail. In general, the reactions of tellurapyrylium salts are similar to those of their oxygen, sulfur, and selenium analogs. The peculiar chemical behavior caused by the presence of a tellurium center is most clearly manifested in the reaction of tellurapyrylium cations bearing dimethylamino groups with halogens. 

Recently it was reported that the salts of tellurapyrylium 25 and tellurachromylium 60 cations can be obtained in high yields (60-85%) by heating, respectively, 4//-tellurapyranes 21 and 4//-tellurachromenes 54 with HPF6 in acetic acid (88MI2). 

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