Phosphetane derivatives

In monocyclic phosphetanes, the P-C intracyclic bond lengths are within the range of 1.93 and 1.81 A (cf. typical values for a P-C bond length, 1.84 A). C-P-C bond angles are smaller than 90° and lie between 76° and 80° and C-C-C bond angles are widened. Selected structural parameters for phosphetane derivatives reported in the decade 1996-2006 are summarized in Figure 6 and Table 3. 

Table 3 Selected bond lengths (A) and bond angles (deg) in phosphetane derivatives...

Bis(trifluoromethyl) peroxide and disulphide have been used in a novel preparation of the difluorophosphoranes (68) from tertiary phosphines. The phosphetan derivative (69), prepared by this route, has been shown to exist as a mixture of two isomers at —100 °C, one of which has a... 

The formation of phosphetan derivatives such as (18) from PCI3, AICI3, and an alkene has been critically re-examined, showing that adherence to a 1 1 1 mixture of the reactants is necessary for success/ Deviations from these ratios lead to a number of by-products these have been identified and their formation has been rationalized. 

There is a single example of enantioselective deprotonation of phosphetane derivatives, reported by Imamoto and co-workers.They prepared a Cj-diphosphine borane (abbreviated as DiSquareP ) by enantioselective deprotonation of 1-tert-butylphosphetane borane, 114 (Scheme 5.46). 

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... 

The thio-Wittig reaction, like the Wittig itself, may involve (thia)phosphetane or betaine-type structures as intermediates. A combined experimental and theoretical study over a wide range of conditions and of substrates (aliphatic vs aromatic, aldehyde- vs ketone-derived) suggests a mechanistic continuity, with solvent polarity and substrate electronic effects being the main influences on the transition from one mechanism to another. ... 

The phosphetanes are rather scarce and present an open field of research. The parent phosphetane and its phosphorus derivatives (P-CN = 3 or 4) are still unknown. The only synthesis, first developed in 1962 (62JOC606), involves addition of PC13 in the presence of AICI3 to a number of highly substituted alkenes in CH2CI2 at 0 to -10 °C (equation 72). 

In preliminary studies, some of the bis-phosphetanes 71, 80, 81, and 82 have been tested in the hydrogenation of model dehydroamino acid derivatives. Selected results are given in Equation (14) <1999SL1975, 1999TL8365, 2004TA2169>. 

However, when the same reaction is performed with camphcne. two main products are formed, the phosphetane 15 and the noncyclic chloro(methyl)phosphino derivative 16 15 is obtained in the optically active form ([a]D —9.4, ee not given), while 16 is racemic13. 

The steric effects of Jpc in P " compounds are less than in P" compounds but still discernible, as shown by a study of derivatives of the phosphetan... 

In marked contrast to tri-covalent nitrogen, tri-covalent phosphoms has a significant barrier to pyramidal inversion, as discussed in section 10.2. In C-substituted phospholanes and the 4-membered phosphetanes as well, cis,trans isomers are stable and separated easily. This possibility was not recognized until it was demonstrated in 1965 that 1,2-dimethyl derivatives 10.12 and 10.13 of dihydrophospholes, which are known as 3-phospholenes, could be separated by fractional distillation or gas chromatography. ... 

Parent phosphetane, (CH2)3PH (Table 6.18) is not yet known, but many derivatives have been prepared. Some phosphetanes are of interest because of their restrictive effect on pseudorotation (Chapter 14.3). 

Phosphide anions are excellent nucleophiles and are very reactive to alkylating agents and metal-lophosphine derivatives are of importance as phosphide transfer agents. Lithium diphenyl phosphine can be used to prepare water-soluble phosphines. Dilithium phenyl phosphine can be used in the synthesis of phosphiranes, phosphetanes and so forth (Chapter 6). Lithium bis(trimethylsilyl)phos-phanide, LiP(SiMe3)2, is useful for the synthesis of compounds with P-Si linkages (Figure 9.11). 

Folded V-ring phosphetanes of type (9.56) have been made [23] as well as derivatives such as (9.57a,b) and six-membered ring compounds (9.57c). 

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. " ... 

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... 

The coupling of 3-tert-butyl [1 - " C]malonate (393) with the /3-amino acid derivative 395 to give amide 396 was developed as an alternative route to the 1,4 addition of 395 to the corresponding [l- " C]acrylate 394, which might have failed due to radiation-induced polymerization. Subsequent treatment with 2,4-bis(4-methoxyphenyl)-l,3,2,4-dithiadi-phosphetane-2,4-disulfide (Lawesson s reagent) followed by Raney nickel-mediated desulfurization of the thioamide function formed converted 396 into the target /3-amino acid ester 397. Intramolecular ester condensation upon treatment of 397 with sodium methoxide and concluding saponification and decarboxylation of the f-butyl ester function afforded the trisubstituted 4-[2- " C]piperidone derivative 398. 

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