Sulfur-based heterocycles

Sulfur-containing heterocycles has been attracted much attention of the chemist due to their potential biological activity, pharmaceutical significance, and wide application in functional materials [3]. Driven by the importance of these structures, great efforts have been devoted toward synthesizing these crucial structures. In recent years, transition metal-catalyzed C-H bond activation to directly synthesize the sulfur-based heterocycles has been numerously studied. 

The Pd-catalyzed C-S/C-H bond activation of simple and diverse bromothio-phenes with alkynes via ring rearrangement to prepare sulfur-based heterocycles and fulvenes was described by Duan and coworkers (Scheme 4.7) [11]. This novel transformation provided a new approach to afford not only the DBTs but also the thiopyrans. 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

A number of nitrogen- and sulfur-containing heterocyclic compounds are effective corrosion inhibitors (62MI11502), the imidazolines and the benzotriazoles being particularly important types. The imidazolines are derived from ethyleneamines by reaction with fatty acids the free bases (53), the fatty acid salts (54), and various derivatives obtained by reaction with anhydrides, isocyanates or alkyl halides (55) are effective inhibitors. 

Heterocyclic thiazyl radicals hold considerable potential in the design of both conductive and magnetic materials. In the pursuit of improved conductivity, a series of resonance-stabilized radicals based on diselenadiazoles, sulfaselenazoles, and diselenazoles were obtained (185-188) (Fig. 17) [298-303], Structural analyses of 187 and 188 (R1 = Me, R2 = H) confirm that lattice and n-delocalization energies are sufficient to prevent solid state dimerization of the radicals. Incorporation of selenium leads to a dramatic increase in conductivity and reduction in thermal activation energy relative to sulfur-based radicals [300],... 

Ozonation of carbohydrate-based heterocycles containing selenium 111 (or sulfur) afford the corresponding selenoxides 113 (or sulfoxides) <2006JA227>. Low-temperature treatment of the initially formed ozonation products leads to Pummerer-like reactions affording interesting selenosugars 114 (Scheme 7). Thiosugars are formed from the... 

Many sulfur-containing heterocycles have potential as materials for inducing electrical conductivity, for example materials based on polymeric thiophenes have been examined for possibilities in electrical conductivity <90SM327>, and cyclopenta- and benzobis-1,3-dithioles and benzothiadiazoles... 

Other direct syntheses of halide free ionic liquids can be categorized into three groups (1) synthesis via N-heterocyclic carbene intermediates, (2) phosphorus based direct reactions with imidazoles and (3) sulfur-based direct reactions with imidazoles as discussed further below. 

By synthesizing bromoalkyl-sulfur and -oxygen based heterocycles, Lautens was able to extend the strategy to include the synthesis of polycyclic thiophenes and furans [83, 84], Under similar reaction conditions to those used for nitrogen-based heterocycles, polycyclic products were obtained in good to excellent yields (Scheme 35). The electronic nature of the aryl iodide had a large impact on the observed yields, as electron-deficient aryl iodides worked well, while little to no product was obtained with electron-rich ones. Based upon these results, Lautens proposed that the mechanism of direct arylation of thiophenes occurs through an electrophilic metalation mechanism. 

Scheme 35 Sulfur-based and oxygen-based heterocycles synthesized via ortho-alkylation/direct arylation sequence...

The strategies described in Schemes 4.6.S-4.6.9 thus combine efficiently a novel sulfur-based safety-catch linker strategy, multigeneration construction of thio-linked pyrimidines with a multidirectional cleavage procedure. This approach should prove successful for the solid-phase synthesis of a whole range of nitrogen-containing heterocycles such as pyrimidines, triazines, imidazoles, benzimidazoles. 

Hexamethyldisilathiane-based thionation of carbonyl compounds as a versatile approach to sulfur-containing heterocycles, particularly, to isothiazoles 05SL1965. 

A low concentration of nitrogen and sulfur heterocycles also can be found in various petroleums. Coal was for years the major source of pyridine-based heterocycles, obtained by pyrolysis in the absence of oxygen (destmctive distillation). An intriguing new detection of heterocycles in nature has occurred in the field of chemistry of the solar system. Pyridine carboxylic acids have been detected in a meteorite that landed in Canada (near Tagish Lake)." Nicotinic acid and its two isomers were isolated along with 12 methylated and other derivatives. 

The study of the chemistry and biology of strained four-membered heterocycles has become an extremely active field of research in 2014. In this chapter, the reader will find a brief discussion of new contributions focused on fields such as organic synthesis and medicinal chemistry. For the sake of clarity, contributions are separated in sections depending on the nature of the heteroatom. Although oxa- and azaheterocycle derivatives dominate the field in terms of the number of scientific pubheations, the chemistry of sulfur-, silicon-, and phosphorus-based heterocycles is also of great relevance.The aim here is not to provide an in-depth analysis of all the vast scientific Hterature concerning four-membered heterocycles during the calendar year 2014. Consequently, there are many examples that are cited but not covered in detail. 

Seed, A. Synthesis of self-organizing mesogenic materials containing a sulfur-based Hve-membered heterocyclic core. Chem. Soc. Rev. 2007, 36, 2046-2069. 

Addition of carbon-based nucleophiles to acetals activated with TBDMS triflate has been reported. In a Mukaiyama aldolization-type reaction, oxygen-, sulfur-, and nitrogen-based heterocyclic silyloxydienes add to chiral electrophilic species derived from the same building blocks (eq 32). All nine possible combinations of nucleophile and electrophile have been achieved. ... 

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