Sulfur heterocycles synthesis

In the synthesis of commercial sulfur-heterocycles two interesting reactions are used (i) diphenylamines may be connected by a sulfur bridge in the orfho-positions (ii) the amino grouping of sulfonamides undergoes condensation reactions with neighboring imino- and amide groups. 

Many other nitrogen- and sulfur-containing rings are available from reactions of the Willgerodt-Kindler type. Benzo- and pyridino-fused thia-zoles, for example, are formed from anilines (benzeneamines) and amino-pyridines, respectively.25 Asinger26 has reviewed the scope of these reactions in heterocyclic synthesis. 

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. 

The use of other phosphorus-sulfur reagents for heterocyclic synthesis appears rare. It would be interesting to investigate in more detail the reaction of compounds, such as the phosphine sulfides, with organic substrates. Triphenylphosphine sulfide is an effective sulfur transfer agent, as it converts oxiranes into thiiranes in good yield. The reaction proceeds with retention of configuration.128... 

The remaining four chapters of the present volume involve topics new to the series. Two of them deal with specific groups of compounds (C. J. Moody on Azodicarbonyl Compounds and T. Sasaki on Heteroada-mantanes ) and two others deal with the Use of Transition Organome-tallic Compounds in Heterocyclic Synthesis (J. L. Davidson and P. N. Preston) and Sulfur Transfer Reagents (M. Davis). 

Intramolecular cyclization of 2-lithiobenzyl-2-halophenyl amines, ethers, and thioethers—Synthesis of phenanthridine, dibenzopyran, and dibenzothiopyran derivatives Having demonstrated the efficiency of this methodology for the preparation of indole derivatives, we prepared the 2-fluoro-phenyl ether and thioether 22 a, b to study their potential as substrates that could afford oxygen and sulfur heterocycles. However, treatment of 22 a, b with fBuLi afforded, after... 

The final chapter in this volume covers the use of sulfur monochloride in the synthesis of heterocyclic compounds and is by O.A. Rakitin and L.S. Konstantinova (Zelinsky Institute, Moscow, Russia). It includes a survey of the extensive work carried out by these authors and other friends and associates of the late Charles Rees on heterocycles containing heterocycles with up to five sulfur atoms and often many nitrogen atoms. In addition, the chapter also shows how sulfur monochloride may be used advantageously in the synthesis of other sulfur heterocycles. 

Synthesis of Oxygen-containing Derivatives of Sulfur Heterocycles by Catalytic Liquid-phase Oxidation V. P. Litvinov and T. V. Shchedrinskaya, Ratal. Sint. Org. Soedin. Sery, 1979, 27-37. 

N,N- Diethylselenopropionamide has been used for the introduction of selenium in the synthesis of some aryl-substituted selenolo[3,4-6jbenzofurans (306). Alkylation of this selenoamide with appropriate halides led to the benzannellated diheteropentalenes (306) via the cyclization of intermediate selenouronium salts (305), by analogy with the synthesis of the corresponding sulfur heterocycles (Scheme 103) (78JHC589) (Section 3.18.5.2.1). 

There is a rich synthetic potential for enamines in heterocyclic synthesis. Enamines can react as electrophiles or nucleophiles and as new partners in cycloaddition reactions. Various derivatives of nitrogen-, oxygen-, and sulfur-containing heterocycles have been prepared, and these, in turn, are of interest as starting materials for additional syntheses. They represent potential synthons for the development of various new directions in organic chemistry. 

Formation of a bond between two heteroatoms in the cyclization step is comparatively rare in heterocyclic synthesis. However, in these polyheteroatom systems it is quite common to form such a bond, particularly between nitrogen and sulfur. 

A variety of cycloaddition processes have been employed in the synthesis of oxygen and sulfur heterocycles. Intramolecular [ 4 + 4] and [ 2 +. 2] additions in suitably designed molecules, for example, have proved useful in this connection. Di-(a-naphthylmethyl)ether (371) is converted in this way to adducts 372 and 373,316 and similar transformations have been... 

Cyclizations arising by intramolecular radical addition have been widely employed in the synthesis of oxygen and sulfur heterocycles. The tetra-hydrofuran derivatives (494) have been prepared in this way via alkoxyl radicals, generated in turn by photolysis of the unsaturated nitrites (495).431 Bridged oxabicyclic compounds have been similarly prepared,432 and the photodecomposition of a nitrite has been employed in the synthesis of the... 

Preliminary results on the enantioselective formation of sulfur and nitrogen mediumsized heterocycles by base-induced ring opening of hetero-oxabicyclic [3.2.1] and [3.3.1] systems have been reported.91 The reaction involves a deprotonation-C—O bond elimination sequence. The kinetics and mechanism of gas-phase unimolecular elimination reactions of some substituted aminoazoles have been studied as an aid to heterocycle synthesis.92... 

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