Tellurium atom, 6-membered heterocycles

Six-membered heterocycles with one tellurium and two nitrogen atoms in the ring are represented by 2-aroyl derivatives of 1,2,3-telluradiazine and 5,6-benzo-1,2,3-telluradiazine 89. For the synthesis of these compounds, IV-aroylhydrazones of 2-bromotellurenylcyclohexenealdehyde and 2-bromotellurenylbenzaldehyde 90 were used as the starting materials (98ZOK959). Dehydrobromination of the hydrazones 90 occurs on treatment with triethylamine and gives the heterocycles 89 in about 80% yields. 

III. Bicyclic Six-Membered Heterocycles with a Tellurium Atom in Position 2. .. 53... 

Volume 63 of Advances in Heterocyclic Chemistry comprises five chapters, from five different countries. In Chapter 1,1. D. Sadekov and V. I. Minkin (Rostov, Russia) have provided the first comprehensive survey since 1984 of six-membered heterocycles containing a tellurium atom. These compounds, which show many differences to their sulfur and selenium analogs, are of potential importance for materials applications. 

Christiaens LEE (1996) Six-membered rings with one selenium or tellurium atom. In Katritzky AR, Rees CW, Scriven EFV (eds) Comprehensive heterocyclic chemistry II. Pergamon, Oxford, chap 5.11, p 619... 

The chemistry of six-membered heterocycles containing one selenium or tellurium atom was initially covered in CHEC-11(1996) (chapter 5.11). This updated chapter primarily deals with material dating from 1993 and is complete to 2005 with occasional references from 2006. The structures and nomenclature of the selenium- and tellurium-containing heterocycles discussed in this chapter are included in Figure 1. One major review of tellurium-containing heterocycles has appeared . The chemistry of thiopyrans, selenopyrans, and telluropyrans has also been reviewed <1994AHC180>. 

A number of theoretical studies of six-membered heterocycles containing one selenium or tellurium atom were previously described in CHEC-II(1996) (section 5.11.2). All of these consisted of ab initio calculations. Several new reports have appeared since this time dealing with theoretical approaches to understanding the properties of these materials, their preparations, and their reactivity. 

Very few structural investigations have been made for five-membered heterocycles containing selenium or tellurium and one other chalcogen atom by either theoretical methods or X-ray diffraction. The lone theoretical treatment <8lJST(7l)l) was a MINDO/3 optimization of molecular geometry for l,3-thiaselenole-2-thione and -2-selenone and for 1,3-diselenole-2-selenone (8) and -2-thione. These molecules were predicted to be planar. The calculated bond lengths and angles for (8) are shown in Scheme 3. 

The syntheses of monocyclic five-membered heterocycles containing one selenium or tellurium atom and one other chalcogen atom can be classified into four groups, according to the number and types of building blocks required to form the ring in a one-step process ... 

Table 15 Ring Syntheses of Five-membered Heterocycles containing One Selenium or Tellurium and One Other Chalcogen Atom ...

Aryl tellurium halides with suitable substituents in the ort/io-position to the tellurium atom cyclize to form heterocyclic compounds with tellurium as a ring-member. 

In the tellurazole series, the structure of 2-phenylbenzotellurazole has been reported <89KGS1690>. The structure shows that the heterocyclic five-membered ring is planar, but due to the bulkiness of the tellurium atom a relatively narrow C— Te—C angle (78.6°) is observed, whereas the C—N—C angle is larger (116.9°) as compared to the angles in a corresponding benzothiazole. 

Previously, the synthesis of flve-membered heterocycles containing sulfur, selenium, and tellurium was reported by Sibor and Pazdera (1996). Two different kinds of heterocycles (93-95) can be prepared by the reaction of substrates (92), a chalcogen atom, and isothiocyanate or ketones in the presence of triethylamine under ultrasonic conditions (Scheme 8.29). Beyond the utilization of ultrasound, the authors studied the use of conventional conditions, as well as microwave irradiation. 

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