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 bistricyclic 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 ratios 21 (10):35 (11):44 (12) (in addition to 9H-selenoxanthene (13) and 9H-telluroxanthene (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 reactions were chalcogen selective with a preference towards the tellurium-bridged bistricyclic ethanes.