Phosphetane oxides

Figure 5 Solid-state geometries for phosphetane oxides.

The McBride synthesis has been applied to the preparation of chiral phosphetane oxides by the reaction of optically active dichlorophosphines with 2,3,3-trimethyl-l-butene. Thus, myrtanyl-, bornyl-, and isopinocamphenyldichloro-phosphines afforded the corresponding phosphetane oxides having chirality localized on both the phosphorus substituent and the phosphorus center. In all cases, epimeric mixtures are obtained (Equation 22) <1997JOC297>. 

In addition to the conventional McBride synthesis using simple alkenes, a few other unsaturated substrates serve as starting materials for the construction of phosphetane rings. For example, the reaction of norbornadiene with chlorophosphines (ClP(OEt)2), instead of dichlorophosphines, afforded tetracyclic phosphetane oxides (Equation 23) <1996JHC979>. 

Trichlorosilane is a very powerful reducing agent. On its own or mixed with mildly basic amines or phosphines it leads to products with retention of configuration in the reduction of acyclic phosphines (entry 1) whereas with more basic amines it affords inverted phosphines (entries 2 and 3) with the exception of phosphetane oxides (entry 4). Entry 3 shows that the famous ligand DiPAMP was prepared for the first time using this reagent. Hexachlorodisilane has... 

The diastereomeric phosphetane oxides 81 were obtained in equimolar amounts (unlike analogous phosphetane oxides bearing other chiral groups derived from pinene) and could be separated by column chromatography. " ... 

The chemistry of phosphetane oxides 81 has been studied in detail. The most important discovery is that it can be diastereoselectively deprotonated with n-BuLi or LDA to give stabilised carbanions 82, which react with a wide variety of electrophiles to give ot-substituted phosphetane oxides (Scheme 2.30). 

With this procedure ot-alkylated (83), brominated (84), formylated (85), silylated (87 and 89), phosphorylated (88) and hydroxylated (90)198.199 phosphetane oxides have been prepared. Usually the products are present as a single diastereomer, with retention of configuration at the phosphorus atom and with the new substituent installed in the equatorial position, in anti disposition to the menthyl group, as confirmed by X-ray crystallography. Cl- and C2-symmetric phosphetane dioxides or diboranes (88, 89 and 91) have also been obtained. Further elaboration has allowed the preparation of derivatives with multiple stereogenic centres (86). Most of the phosphetane oxides of Scheme 2.30 have been reduced to the parent phosphines... 

In the solvolysis of a series of derivatives of phosphetan-1-oxide (80) it has been observed that, when X = NMeg or Cl, rates were lower than for comparable acyclic analogues whereas when X = OR the converse was true. Making the assumption that all these displacements proceed by way... 

Dimethyl-l-phenyl-3-vinyl-phosphetan-l-oxid m-, 20% Sdp. 10570,05 Torr (6,5 10 kPa)... 

The majority of the publications in the field of oxidative addition of HFA to tertiary phosphanes deal with the formation and properties of l,3,2-A -dioxaphospholanes 57 (60,61). These compounds are generally stable when the a carbon atoms do not bear hydrogen atoms. Heterocycles with a hydrogen atoms are stable up to about 70°C at this temperature the isomeric phosphetanes are formed. The syntheses of some sterically hindered phosphoranes require drastic conditions. 

Phosphetan 1-Phenyl-2,2,3,3-tetra-methyl- -1-oxid E2, 29 (En + R-PC12)... 

Dichlorophenylphosphine, on treatment with 2,4,4-trimethy]-2-pentene, forms a cyclic phos-phonium salt, which on hydrolysis gives a mixture of diastereomeric phosphetane 1-oxides 5. The ratio of diastereomers is affected by the method used to quench the intermediate salt8. 

Re-examination of the formation of the alkyl esters of trans-1-ch loro-phosphetan 1-oxide (45 X = C1) points to the production of both cis- and... 

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