Phosphonyl oxides, phosphonylation with

Without additional reagents Phosphonylation with phosphonyl oxides... 

Recently, Fossum et al. prepared several phosphine-oxide-containing monomers (Scheme 6.23).163 These monomers were used to prepare hyperbranched polymers in a typical aromatic nucleophilic substitution. However, only oligomers with M lower than 2500 g/mol were obtained. These results did not surprise us, since our previous work demonstrated that the para-hydroxyl group of the phosphonyl group is not very reactive and would require higher reaction temperatures.11... 

Support-bound, enantiomerically pure alcohols can be converted into phosphonates by Mitsunobu esterification, which results in complete inversion at the stereo-genic center. This strategy has been used to prepare peptidyl phosphonates on solid phase. These are interesting transition-state analogs with potential utility as peptidase inhibitors (Figure 11.3 [12,13]) or tyrosine phosphatase inhibitors [14]. Serine or threonine derivatives can be converted into phosphonates by direct phosphonylation with an activated monoalkyl phosphonate [15] or by treatment with phosphonamidites RP(OR)NR2 in the presence of tetrazole followed by oxidation [16]. 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

This chapter covers the main synthetically useful phosphonylation reactions, the corresponding processes of phosphinylation and tertiary phosphine oxide formation along with some related reactions. In all these reactions the phosphorus reactant (a phosphite, phosphonite, phosphinite, or derivative or tautomer thereof) is the nucleophilic component, herein these reactants are referred to collectively as phosphorus(III) reactants/acids, as appropriate in general these reagents are best used freshly distilled. Syntheses of phosphonates, phosphinates and tertiary phosphine oxides by nucleophilic substitution at phosphorus is not covered (for reviews of this area see Refs 6 and 16). 

Phosphonylation of a -3-(9-isopropylidene-a -pyridoxyl chloride via a Michaelis-Becker reaction, followed by deprotection with 1 M HCl and oxidation of the resulting primary alcohol with MnOj, produces diethyl (4-fonnyl-3-hydroxy-2-methyl-5-pyridyl)methylphosphonate (Scheme 5.38), an analogue of pyridoxal 5 -phosphate whose 5-position side chain has been replaced by a phospho-nomethyl group. The alcohol oxidation step can be accomplished with a wide range of reagents, such as activated MnOj in CHCI3 at room temperature (53%), PCC in CH2CI2 (83-86%), or the Swem reaction (>95%). ... 

The oxidative cleavage of 1,2-diols with NaI04 appears to be a powerful method to prepare phosphonylated aldehydes with variable carbon chain lengths. It has been applied successfully to the synthesis of diethyl l-(ethoxycarbonyl)-4-oxobutylphosphonate, a precursor in tlie preparation of glycinoeclepin A, in 70% yield (Scheme 5.41). ... 

Phosphonylation and formylation reactions can be used successively in multistep procedures. For example, 1,3-/ .v(brornornclhyl)benzene undergoes an initial phosphonylation through Michae-lis-Becker or Michaelis-Arbuzov reactions, followed by oxidation of the benzylic bromide with 2-nitropropane and EtONa (Scheme 5.52) or Fe/HiO to give the corresponding 3-formyl-bcnzy I phosphonate in satisfactory overall yield (30-37%). 

Diethyl 4-formylalkylphosphonate can be prepared in almost quantitative yield (98%) through the mild oxidation of phosphonylated l,2-didcoxy-3,4 5,6-di-O-isopropylidcn-i)-arabinose with NalO4 at 0°C in H2O or a H2O/EtOH mixture. ... 

Phosphonylated aldehydes are oxidized to the corresponding phosphonylated carboxylic acids by peracids at room temperature or by alkaline KMiiO -" in quantitative yields. The same compounds can be obtained, even more simply, by combining the hydrolysis and oxidation steps. Thus, diethyl 2,2-diethoxyethylphosphonate can be first hydrolyzed with 2 M HCl and then oxidized with 78% peracetic acid to give diethyl l-(hydroxycarbonyl)methylphosphonate in almost quantitative yield (93-97%) without isolation of the intennediate aldehyde.- ... 

An attractive procedure for the preparation of 2-oxo-m-(alkoxycarbonyl)alkylphosphonatcs involves the C-phosphonylation of p-keto ester dianions with dialkyl chlorophosphate (45-67%) or C-phosphirylation of the monoanion of substituted dioxinones with diethyl chlorophosphite followed by oxidation ... 

A number of 1,4,2-benzodioxaphosphinines have been synthesized, all at the formal 2,3-dihydro level of oxidation. Synthetic approaches vary from the straightforward (base-induced catechol cyclization with chloromethyl phosphonyl or phosphinyl chlorides) to the exotic (cycloadditions of phosphaalkenes to o-quinones). 

Oxidative phosphonylation of aromatic compounds with phosphorus(lll) esters... 

Similar reactions can lead to the formation of two P-C bonds. For example, Pd-catalyzed addition of 7 (a privileged substrate which is often more reactive than other H-phosphonates) to terminal alkynes led to dehydrogenative double cis phosphonylation (Scheme 9). A Pd(II)/Pd(IV) cycle was proposed. Reaction of [Pd(allyl)Cl]2 with 7 gave chloro-bridged dimer 8. Alkyne insertion into the Pd-P bond was then proposed to give alkenyl intermediate 9. P-H oxidative addition would then yield hydride 10, whose reaction with 7 was proposed to lead to P-C bond formation and loss of H2 [18]. 

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