- Zinc-mediated reductive dimerizations of telluroxanthone and selenoxanthone. Tellurium-selenium selectivity
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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. (C) 2000 Elsevier Science Ltd.
- Levy,Agranat
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p. 6157 - 6160
(2007/10/03)
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- Organosulfur Compounds, L. - 2H-Thiopyrans and Dihydro-2H-thiopyrans, Synthons for Thiophenes
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2H-Thiopyran derivatives yield thiophenes on pyrolysis at 240-260 deg C.The influence of substitution in positions 3 to 6 of the 2H-thiopyrans on these new thermal rearrangement and fragmentation reactions is dealt with, and some proposed mechanisms are discussed in detail.A novel three-step synthesis of thiophenes from carbonyl compounds via the corresponding thiones, their -cycloaddition with 1,3-dienes with formation of dihydro-2H-thiopyrans and subsequent thermal conversion is described.In this reaction sequence, whose scope and limitations are outlined, t he thiocarbonyl compound contributes the sulfur and the 1,3-diene the carbon skeleton of the desired thiophenes.
- Praefcke, Klaus,Weichsel, Christian
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p. 1604 - 1619
(2007/10/02)
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