Oxygen heterocycles, literature

The thiopyranofurans contain a six-membered sulfur heterocyclic ring and a five-membered oxygen heterocyclic ring (Table 10). Another common name for these isomers is furothiopyrans. Not much chemical literature exists regarding the thiopyranofuran compounds. 

The three-membered oxygen heterocycle, or oxirane (Figure 1), is also described in the current literature as an (l,2-)epoxide, an oxacyclopropane, or, using additive nomenclature, an ethylene oxide. 

Thionyl chloride (SOCl2) is the most versatile of all sulfur transfer reagents in heterocyclic synthesis. The sulfur-oxygen bond renders the sulfur atom more electrophilic the possibility of ready removal by elimination of the oxygen atom allows easy aromatization of many of the initially formed sulfur heterocycles. Two general reviews of the chemistry of thionyl chloride are available.53 Both cover the literature up to about 1970. 

Despite the authors assertion that alkylated heteroaromatic compounds provide a better model for fuel-bound nitrogen than do the unsubstituted heterocycles, their pyrolytic study remains the most comprehensive look at substituted heteroaromatic chemistry, even several years later/ Kinetic studies are more common in the literature Frerichs et al. examined the reaction of the picolines with oxygen atom, while Yeung and Elrod studied reactions of HO with pyridine and its methyl- and ethyl-substituted derivatives.Both groups noted that the presence of nitrogen did not demonstrably affect the species chemistry generally, reactivity is comparable to toluene. 

Of the possible four-membered sulfur-containing heterocyclic rings that contain another heteroatom, which is not sulfur, oxygen, or nitrogen, only the thiaphosphetanes, silathietanes, and selenathietanes are discussed in the literature up to 1980. 

The literature contains examples of virtually all heterocyclic systems with two heteroatoms of nitrogen, sulfur and oxygen. However, in some cases simple derivatives of the parent... 

The abundance of six-membered oxygen containing heterocycles in bioactive natural products continues to encourage the development of new and improved syntheses. There is a vast amount of new literature dedicated to the synthesis of pyrans and their benzo derivatives however, many traditional approaches are still of great value and this chapter should be read in conjunction with the corresponding chapters in the first and second editions of Comprehensive Heterocyclic Chemistry <1984CHEC, 1996CHEC-II>. 

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