Heterocycles from dihalides

The required hydrogenated heterocycles can easily be prepared from dihalide compounds if the principle of dilution213 is observed (Eq. 3). The... 

The heterocyclic tellurium compounds can also be isolated from the reaction mixtures by extraction with dichloromethane and distillation3 or by precipitation of the telluracyclohcxane dihalides upon addition of elemental halogens to the extracts4. 

Diorgano tellurium dihalides were prepared in this manner from dialkyl, alkyl aryl, and diaryl tellurium compounds, and from tellurium heterocycles. However, 1-oxo-1,3-dihydro-2-benzotellurophene experienced ring cleavage when reacted with sulfuryl chloride7. 

Dimethyl-10-ethylphenotellurazine reacted with sulfuryl halides1 or bromine2 in diethyl ether solution to quantitatively precipitate Te, 7e-dihalides. The dihalides were recrystallized from chlorobenzene. The dihalides can be reduced to the parent heterocycle with hydrazine3 or sodium sulfide4. 

The synthesis of chiral phosphine oxides has stimulated effort in a number of laboratories in recent years. An elegant new approach to the problem involves the use of sugar-derived phosphorus heterocycles. These are 1,3,2-dioxa-phosphorinan-2-ones, such as (1), formed from glucosides and various phosphonic dihalides, such as (2). The preparation of chiral phosphine oxides... 

Nitrogen can be incorporated in the macroring by inclusion of a small-ring nitrogen heterocycle such as pyridine or pyrimidine. Three approaches should be noted. If the pyridyl unit is incorporated as a 2,6-bis(methyleneoxy)pyridine derived from lutidine, the precursor will normally be a lutidine dihalide or diol. In the case of sulfur, the diol would be a dithiol. If the pyridyl unit is to be attached by 2,6-aminomethyl groups, amide formation followed by reduction is a possibility. In the event that the heterocycle will be attached directly to a macroring heteroatom, nucleophilic aromatic substitution may be useful. 

Thus, reaction of carbonimidoyl dihalides with a wide variety of nitrogen-containing substrates can be achieved, and the products obtained range from linear chloroformamidines, guanidines, and carbodiimides to five- and six-membered heterocycles. 

Hilborn et al. demonstrated the synthesis of PBOs (Figure 5.29) by polymerization of bis(fluorophenyl benzoxazoles) with bisphenols. This polymerization was based on the activation of the fluoro group toward nucleophilic aromatic substitution by the oxazole component of the benzoxazole heterocyclic [51]. The TgS of the poly(arylene ether benzoxazoles) ranged from 213 to 303 °C, depending on the bisphenol and activated dihalide used in the synthesis. Generally, the TgS increased with the bulkiness of the bisphenol used. The polymers containing the >C(CF3)2 unit in both the benzoxazole and the bisphenol moiety in the monomers showed higher solubility (NMP) compared to the other PBOs. The physical properties of fluorinated poly(arylene ether benzoxazole) s are presented in Table 5.3. 

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