| Research Abstract |
1. The treatment of 1-benzotellurepines, novel seven-membered heterocycles, with t-BuLi followed by addition of a metal reagent (Cl_2SnBu_2, Cl_2SbPh and Cl_2SiMe_2) afforded the corresponding 1-benzostannepines, 1-benzostibepines and 1-benzosilepines, respectively, in one pot via the tellurium-lithium exchange.
2. The 1-benzostannepines, which were prepared from (Z)-1-(o-bromophenyl) but-1-ene-3-ynes, were easily converted into the 1-benzostibepines and the 1-benzoborepines by tin-antimony and tin-boron exchange reactions in moderate to good yields, respectively.
3. The general preparation of the unsubstituted and 2-substituted 1-benzoselenopyrylium salts from the selenochromen-4-ones via the selenochlomenes is investigated.
4. The reactions of the stable 1-benzoselenopyrylium salts with several nucleophiles and also LiAlH_4 reduction are described ; comparison of the behavior of 1-benzotelluropyrylium salts is made.
5. The treatment of the 1-benzoselenopyrylium salts with an alkyl(phenyl
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)magnesium halide resulted in nucleophilic addition at the C-4 position to give the corresponding 2,4-disubstituted 4H-selenochromenes in good yields, respectively. The obtained selenochromenes were men easily converted into the 2,4-disubstituted 1-benzoselenopyrylium salts.
6. The treatment of the tellurochromen-4-ones with several Grignard reagents gave the 4-substituted 4-hydroxy-4H-tellurochromenes in good yields, respectively. The obtained compounds were readily transformed into the 2,4-disubstituted 1-benzotelluropyrylium salts.
7. The regioselective and stereospecific intramolecular ring closure reactions of o-ethynylbenzyl tellurols and o-ethynylbenzyl selenols, which were readily. generated by the reaction of the o-ethynylbenzyl bromides with sodium hydrogen telluride (NaHTe) or sodium hydrogen selenide (NaHSe), produced the isotellurochromenes and isoselenochromenes together with (Z)-1-methylidene-2-tellurahidans and (Z)-1-methylidene-2-selenaindans, respectively. The obtained isochromenes and were transformed into the corresponding 2benzopyrylium tetratluoroborates, respectively. An X-ray structural analysis of the 2-tert-butyl denvatives is also described. Less
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