Phosphorus-selenium rings

PNICTOGEN-CHALCOGEN RINGS 11.7.1 Binary Phosphorus-Sulfur and -Selenium Rings... 

The (5,5)-fused bicyclic ring system with one fusion nitrogen atom and three additional heteroatoms in a 2 1 distribution over both live-membered rings (2N1) allows for a large variety of conceivable structures. The additional heteroatoms are mainly nitrogen, oxygen, and sulfur a few representatives of (5,5)-fused ring system also contain phosphorus, selenium or silicon atoms. 

The aim of this Report is to review new methodology for the synthesis of saturated heterocyclic compounds. Emphasis is placed on reactions which involve a cyclization step and few ring transformations are described. Heterocycles which contain phosphorus, selenium, and silicon as the heteroatom are omitted. A few key steps in complex natural product syntheses are mentioned, but carbohydrates are excluded. The rapidly increasing numbers of reports describing the synthesis of saturated and unsaturated lactones and of crown ethers are covered in Chapters 3 and 10. 

Larger chalcogen-phosphorus heterocycles, although less common in the literature, are accessible via a variety of synthetic routes.2,83,84 For example, the cyclic trimer (SPR)3 (R = 2,4,6-tri-tert-butylphenyl) contains a puckered six-membered P3S3 ring and is produced in the reaction of a phosphinic chloride with lithium sulfide (Equation 73).98 Additionally (R P)3Se5 (R = 2,4-di-tert-butyl-6-wopropoxyphenyl), synthesised from the oxidation of a primary phosphine with three equivalents of elemental selenium (Equation 74), has... 

Selenium, and Phosphorus Atoms in the Five-Membered Ring 714... 

Ring Synthesis of Fused Pyridazines, Pyrimidines, and Pyrazines with Oxygen, Sulfur, Selenium, and Phosphorus Atoms in the Five-Membered Ring... 

A-Alkyl-2,1,3-benzoselenadiazolium salts react with sodium hydroxide with elimination of selenium to give A-monoalkyl-o-phenylenediamines <89SC1381>. The thiaselenazolines (38a) and the diselenazolines (38b) are attacked by trialkyl phosphites at Se with elimination of selenophosphate and incorporation of phosphorus into the ring (87) in place of selenium (Equation (8)) <80CB2699>. 

Electrophilic attack at ring silicon, sulfur, selenium, and phosphorus Nucleophilic attack at ring silicon Nucleophilic attack at ring boron... 

Se NMR spectra of selenadiphospholes and diselenaphospholes 44, 45, 78, and 47 were reported (Table 25) <2002CEJ2705>. In compounds 44, 45, 78, and 47, the exocyclic selenium atom is at lower frequency relative to those within the heterocycle. A l/(Se,Se) coupling of 271 Hz is characteristic of compound 45. In molecule 47, the ring atom Se-3 has a 2/(P,Se) coupling to the phosphorus(v) center P-1 of 20 Hz. On the other hand, there is no resolved coupling between the exocyclic Se-1 and the internal phosphorus(m) center P-2. 

The analogous phosphorus heterocyclic systems that include selenium or tellurium are discussed in detail in Chapter 6.12, and the systems incorporating phosphorus and arsenic or antimony are covered in Chapter 6.14. In addition, numerous examples of five-membered heterocyclic systems with phosphorus and elements of group III (B, Al, Ga, In) and group IV (Si, Ge, Sn, Pb) are included in Chapters 6.16 and 6.17 of this volume. The systems with five heteroatoms in a five-membered ring (e.g., pentaphospholide anion and tetrazaphospholium cation) and the fused heterocyclic rings (see Volumes 9-11) are beyond the scope of this chapter and are not covered here. 

Oxidation of a A3-phosphorus atom of stable P-heterocycles is a general reaction, which leaves the basic ring structures intact in many cases. This includes the conversion of l,2-dihydro-lA3,2A3-diphosphete derivatives like lc, for example, to form l,2-dihydro-lAs,2A3-diphosphete 22. Oxidation agents used are elemental selenium or [(CH3)3Si]202 <1997CB1519>. Upon photolysis lc rearranges partly into its m-isomer Id. The mixture of isomers can be reconverted completely into the trails-isomer lc by heating <1997JOC7605>. 

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