Phosphorus Containing Ring Systems

9 Phosphorus-containing Ring Systems. - A range of new chiral oxazaphospholidine oxides 266 and 267 have been synthesised and used as catalysts in asymmetric reductions of ketones with diborane. Mannich-type cyclisation reactions of 5-amino-3-benzylthio-4-cyano(ethoxycarbonyl)pyrazoles with dichlorophenylphosphine and aromatic aldehydes in the presence of cation exchange resin have been used to prepare a number of 6-oxo-6-phospha-4,5,6-trihydroimidazolo[l,2-b]pyrazoles, e.g. 268. Some of these compounds have herbicidal activity and this report is typical of a number of similar ones in the Chinese literature. A number of metallocycles, e.g. 269, have been reported as products from reactions of transient zirconocene-benzyne intermediates with phosphaimines followed by sulfuration or selenation.  

If encouraged to proceed further, some of the reactions already mentioned will allow ring formation to occur. In boiling benzene, the product (294) (Section 

8) cyclizes to l,2-dihydro-3-methoxy-l-methyl-2,5-diphenyl-l,3-azaphosphole 

3- oxide (295) and similarly in boiling benzene, the readily formed (296) (Ar = 

Reference has already been made to the formation of phospholanes from 1,4-diketones and bis(trimethylsilyl)phosphonite. The phosphorinanes (299) (R = 

or Ph) have been obtained by using the same reagent and the appropriate 

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Two phosphorus-containing ring systems and one silicon-containing fused heterocycle belonging to the hetero-atomic arrangements of this chapter have been synthesized recently. The synthetic pathways are presented in Scheme 25. 

Ring Synthesis of Phosphorus-Containing Ring Systems 905... 

Also, 13C NMR assignments have been published for a recently synthesized phosphorus-containing ring system imidazo[l,2-r-][l,3,2]oxazaphosphinine 49 <1996TL977>. The chemical shifts as well as the /C P coupling constants are shown in Table 2. 

Phosphorus-Containing Ring Systems. - The chiral a-diazophosphonic acid derivatives (289), (290) and (291) have been prepared from (-) ephedrine and (S,S)-N,N -dimethyl-l,2-diaminocyclohexane. Preliminary experiments suggest that the new chiral auxiliaries investigated exert little influence over the subsequent reactions of the derived rhodium (II) acetate-catalysed O-H and N-H insertion reactions. ... 

Phosphorus Containing Ring Systems. 1-Acyl allyl phosphonates (376) exposed to the action of m-CPBA in the presence of MgS04 are readily cyclized... 

For the most part, theoretical methods have been applied to the question of the aromaticity of the various phosphorus-containing ring systems, and this question is relevant only to systems with complete cyclic 7r-conjugation. Applications to other areas have been rare. 

There are very many compounds based on simple phosphorus-containing ring systems, such as those represented by structures 3 and 4, which are essentially of the phosphonic or phosphinic acid types. To the extent that they are also heterocyclic compounds of phosphorus, their chemistry has also been considered separately... 

The best known boron-containing ring systems are the so-called inorganic benzenes, namely, borazine (71), boroxine (72), and triphosphatriborin (73) (Fig. 46), which are isoelectronic and isostructural with benzene. These ring systems are obtained by the interaction of boron with nitrogen, oxygen, and phosphorus, respectively.4... 

Photolysis of 2,3,5,6-tetrakis(trifluoromethyl)-l,4-di hoshabenzene gives 1,3,4,6 tetrakis(tnfluoromethyl)-2,5-diphosphatncyclo[3 1 0 0 ]hex-3-ene, an ana logue of benzvalene containing phosphorus atoms in the ring system [267, 16S] (equation 40)... 

The EPR spectra of the related 1,2,4,6,3,5-thiatriazadiphosphinyl radicals (3.20) reveal a distinctly different electronic structure.The observed spectrum consists of a quintet of triplets consistent with coupling of the unpaired electron with two equivalent nitrogen atoms and two equivalent phosphorus atoms [Fig. 3.4(a)]. This interpretation was confirmed by the observation that the quintet collapses to a 1 2 1 triplet when the nitrogen atoms in the ring are 99% N-enriched [Fig 3.4(b)]. Thus the spin delocalization does not extend to the unique nitrogen atom in the phosphorus-containing system 3.20. 

Examples of cyclophosphazenes with ring systems containing elements other than phosphorus or nitrogen continue to be reported. The linear phosphazene [Ph2(H2N)Pi N.i P(NH2)Ph2]+Cl is cyclized by antimony pentachloride to give the compound (35). This result contrasts with... 

This chapter provides an update of Chapter 8.33 in CHEC-II(1996) <1996CHEC-II(8)863>. The work carried out on the bicyclic ring systems with ring junction P, As, Sb, or Bi has focused primarily on phosphorus. Very little work has been done on the other heteroatoms and as such the synthesis and reactivity of these compounds have been reviewed as one section, Section 12.12.7. Most of the compounds in this class contain more than one heteroatom, the additional atoms usually being oxygen and nitrogen. 

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