Zinc-mediated reductive dimerizations of telluroxanthone and selenoxanthone. Tellurium-selenium selectivity

Reductive dimerizations of 9H-selenoxanthen-9-one (3) and 9H-telluroxanthen -9-one (4) (1:1) with zinc in boiling AcOH and HCl for 1 hour gave the bist ricyclic ethanes 9,9'-bi(9H-selenoxanthene (10), 9,9'-bi(9H-telluroxanthene ) (11) and 9-(9'H-telluroxanthen-9'-yl)-9H-selenoxanthene (12) in the ratio s 21 (10):35 (11):44 (12) (in addition to 9H-selenoxanthene (13) and 9H-tel luroxanthene (14)). Analogous reactions of 4 and 9H-thioxanthen-9-one (9) ( 1:1) and 3 and 9 (1:1) gave the corresponding bistricyclic ethanes. The rea ctions were chalcogen selective with a preference towards the tellurium-bri dged bistricyclic ethanes. (C) 2000 Elsevier Science Ltd. All rights reserv ed.