Studies on tellurium-containing heterocycles. Part 18.1 Preparation and structure of 2-benzotelluropyrylium salts and 2-benzoselenopyrylium salts

Studies on Tellurium-Containing Heterocycles. Part 20. Reactions of 2-Benzoselenopyrylium Salts and 2-Benzotelluropyrylium Salts with Nucleophiles: Formation of 1-Functionalized 1H-Isoselenochromenes and 1H-Isotellurochromenes

“…The pyrylium salts (1) were also reduced by DIBAL-H to give the 1H-isochromenes (2) in quantitative yields. These compounds (2) were identical with the authentic samples, 16) which were the precursors for the synthesis of the corresponding pyrylium salts (1A) and (1B). The 3-tertbutyl-2-benzopyrylium salts (1Aa) and (1Ba) reacted with excess zinc dust in acetonitrile at 0°C under an argon atmosphere to give 1,1Ј-bis(tert-butylisochromenyl) (3Aa) and (3Ba) in 18 and 15% yield as the sole characterized products, respectively.…”

“…The unsubstituted 29) and 3-substituted 2-benzoselenopyrylium salts 16) have been prepared before, while these selenopyrylium salts (14-17) having two carbon functional groups at the C-1 and C-3 positions are hitherto unknown compounds.…”

“…We have also previously reported the practical and facile preparation [11][12][13] and the reactions 11,14,15) of these 1-benzopyrylium salts. More recently, we succeeded in preparing 16) the stable 2-benzotelluropyrylium 17) and 2-benzoselenopyrylium salts, 18) structural isomers of them; the former is a previously unknown heterocyclic ring system. Therefore, this paper deals with the results of the examination of the reactivity of these novel 2-benzopyryliun salts with various nucleophiles using the stable compounds, 3-tert-butyl and (or) 3-unsubstituted derivatives as easily available pyrylium salts.…”

Thermal Ring Expansion of 2-Azidoselenochromenes: First Synthetic Examples of 1,3-Benzoselenazepines

“…However, no monocyclic and benzene ring-fused selenazepines have yet been reported to the best of our knowledge. Recently, we have succeeded in the construction of the first benzotellurazepine ring system, the 1,5-benzotellurazepinines.10,11) Furthermore, we have focused attention on the syntheses and reactions of the telluro- [12][13][14][15][16][17] and selenopyrylium salts, [18][19][20][21] six-membered heterocyclic cations containing a tellurium or selunium element.Since Le Roux and coworkers 22,23) discovered the conversion of pyrylium salts into 1,3-oxazepines through azidopyran intermediates 25 years ago, several thermal and photo rearrangements of the azide compounds, prepared from pyrylium salts and relatives with sodium azide, have been reported for the purpose of synthesizing seven-membered heterocycles. [24][25][26][27] Among them, neither the monocyclic selenazepines nor benzoselenazepines were prepared by any method including the above ring expansion access from the azide compounds.…”

“…Recently, we have succeeded in the construction of the first benzotellurazepine ring system, the 1,5-benzotellurazepinines. 10,11) Furthermore, we have focused attention on the syntheses and reactions of the telluro- [12][13][14][15][16][17] and selenopyrylium salts, [18][19][20][21] six-membered heterocyclic cations containing a tellurium or selunium element.…”