G. M. Abakarov

Five-Membered Heterocycles with Vicinal Te and O Heteroatoms

Publisher Summary This chapter intends to collect all the data available on the synthesis and reactions of various classes of five-membered heterocycles with vicinal Te and O heteroatoms, and to provide a comprehensive treatment of the subject. The chapter has discussed the synthesis and reactions of 1,2-Oxatellurol-1-ium Halides; 5H-Oxatelluroles-1,2 and 3H-benzoxatelluroles-2,1; 1,10-Spirobis-[3H-benzoxatelluroles-2,1]; and Oxatellurolanes-1,2 and Hexahydro-3H-benzoxatelluroles-2,1. For the synthesis of the heterocycles 42 and 43, two important groups of precursors, 3-aryltelluropropene-2-oles-3 44 and 2-butyltellurobenzylic alcohols 45, have been used. A series of oxatellurolanes-1,2 with various halogen atoms attached to the tetracoordinated tellurium center was prepared in 53%–86% yields by the reaction of dehalogenation of a-halogenocarbonyl compounds (o-chloro-, bromo- and iodoacetophenones, diethylbromo- and diethyldibromomalonates) by 3-organyltelluropropanoles-1. The chloro-containing hexahydro 3H-benzoxatelluroles-2,1 are susceptible to facile anionic exchange reactions occurring under the treatment of their acetonitrile solutions with NaBr, NaI, or AgF. The yields of the products are almost quantitative. Finally, the chapter also discusses about the Molecular and Crystal Structures. The heterocyclic compounds with vicinal tellurium and oxygen atoms, whose molecular and crystal structures have been determined by X-ray analysis are listed in the chapter. It contains data on important structural parameters featuring the stereochemical configuration at the tellurium centers.

Nitrogen-tellurium-containing heterocycles. 4. X-ray structure of 2-phenylbenzotellurazole

The crystal and molecular structure of 2-phenylbenzotellurazole is determined by x-ray methods. The heterocyclic fragment of the molecule is planar. The dihedral angle between planes of the heterocycle and the 2-phenyl substituent is 31.2‡. Somewhat shortened Te-N intermolecular ocntacts (3.43 å) are seen in the crystal. These do not substantially affect the physical properties of the compound.

Nitrogen-tellurium heterocycles

Several 2-substituted benzotellurazoles have been prepared by the reaction of N-allyl derivatives of o-methyltelluroaniline with POC13 or SOC12 followed by reduction of the σ-telluranes which are formed. The use of the zinc and sodium salts of o-aminotellurophenol and 2-chlorotellurenylazobenzene, in a procedure similar to that used to prepare benzothiazoles and benzoselenazoles, did not lead to the formation of benzotellurazoles.

Reactions of immonium and telluronium salts of 2-phenylbenzotellurazole

N-methyl-2-phenylbenzotellurazolinium iodide, like other N-methylbenzochalcogenazolium salts, readily undergoes reduction, hydrolysis, and recyclization with hydrazine hydrate and o-phenylene diamine. 1-Methyl-2-phenylbenzotelluronioazole perchlorate is an effective methylating agent in reactions with nucleophiles.

Heterocycles containing tellurium and nitrogen. 5. Basicity constants of benzazoles

The basicities (pKBH+) of monotypically substituted 2-R-benzochalcogenazoles increase regularly on passing from benzoxazoles to benzotellurazoles.

Nitrogen-tellurium-containing heterocycles. 3. Reaction of 2-phenylbenzotellurazole at the heteroatoms

Reactions of 2-phenylbenzotellurazole at both heteroatoms are studied. σ-Telluranes and molecular complexes with mercury and palladium salts are prepared. Exchange of a tellurium atom by sulfur is achieved. Alkylation of a heteroatom of the pyrrole type, the tellurium atom, is achieved in a series of benzazoles for the first time.