Phosphonites reactions

In 2013, Hackenberger and coworkers [66], in Berlin, reported the cycloaddition of a borane-protected alkyne-phosphonite with azides to form borane-protected triazole-phosphonites (Scheme 9.24). In this reaction protocol, we have a sequence of two different couplings with two different azido reagents in the first, we have a CuAAC cycloaddition, followed by a metal-free Staudinger phosphonite reaction. 

Scheme 9.24 The sequential CuAAC-Staudinger phosphonite reaction, as described by Hackenberger and coworkers [66].

The formation of the phosphoranes (23) in the preparation of the phosphonites (24) has been shownto be due to two processes firstly, the acid-catalysed disproportionation of the phosphonites to give (23) and cyclopolyphosphines and secondly, the remarkable base-catalysed reaction of the phosphonites with catechol to give (23) and hydrogen. 

The mechanism of the Arbusov reaction has been the subject of some study. Intermediates (4), isolated at low temperatures from the reaction of phosphonites with alkyl halides, show n.m.r. chemical shifts in the region of — 95 p.p.m. in a wide variety of solvents. ... 

An earlier report that diethyl t-butylphosphonite (10) did not undergo an Arbusov reaction, presumably for steric reasons, has been withdrawn since the presumed phosphonite is now shown to be the phosphonate. 

A kinetic study of the previously reported substitution of aromatic nitro groups by tervalent phosphorus has established an aromatic 5n2 mechanism. Similarities in values of activation energies, and in relative reactivities of phosphite and phosphonite esters, between this displacement and the Arbusov reaction suggest a related mechanism (31), while the lack of reactivity of p-dinitrobenzene is attributed to the need for intramolecular solvation (32). The exclusive formation of ethyl nitrite, rather than other isomers, is confirmed from the decomposition of triethoxy-(ethyl)phosphonium fluoroborate (33) in the presence of silver nitrite. A mechanism involving quinquevalent phosphorus (34) still seems applicable, particularly in view of the recent mechanistic work on the Arbusov reaction. ... 

Two preparations of diesters of phosphonous acid have been reported, - One of these, which claims to be the first preparation of these derivatives, involves the reaction of ammonium hypophosphite with triaikylsilylamines to give bis(trialkylsilyl) esters (127) in excellent yield. These compounds are extremely reactive, e.g. they are spontaneously inflammable in air. Dialkyl phosphonites (128) have also been prepared by the reduction of... 

In a study of the reactions oi acyclic o-methoxyphenyl-phosphinites (45a), phosphonites (45b) and phosphites (45c) with halogens,the intermediate halogenophosphonium salts (46) are stabilised either by ligand exchange with starting material (not shown) or by elimination of methyl halides to form cyclic phosphoranes ( 47 ) 3 7. ... 

The kinetics of the reaction of trialkyl phosphites, dialkyl aryl-phosphonites, alkyl diarylphosphinites, and triarylphosphines with Sg has been studied the effects of structural changes on the rate (Ph2POR > PhP(OR>2 > P(OR)g > Ph P) and on the Hammett p values are interpreted with respect to the mechanism. A general method to displace mercapto groups from carbon with clean inversion includes... 

The vinylphosphonic esters (77) are obtainable by distillation of the phosphite esters (76)(Scheme 13). No reaction takes place at the vinyl halogen during the preparation of the esters (78), but the interaction of phosphonites and... 

This selectivity for preferred reaction displacing the halide is found withboth P(III) and P(V) mixed halide/ester systems (Equation4.15)38 and has been noted in several patents to be of value for phosphonite synthesis (Equation 4.16).39 40... 

A further selectivity is found with the preferential displacement of aromatic ester linkages compared to alkyl ester linkages using Grignard reagents.41 In the reaction of the chiral mixed-ester phosphonite shown in Equation 4.17, preferential displacement of the aromatic ester compared to the alkyl ester occurs with inversion of configuration at phosphorus.42... 

Reactions in which Phosphorus is Electrophilic.—Further study has been made of the reactions between chlorodialkylphosphines (26) and phosphites or phosphonites.28 By appropriate choice of the alkyl groups in (26), redistribution reactions can be inhibited and good yields of products (27) with P—P bonds are obtained.28... 

Routes to phosphazenes involving the reaction of phosphines with carbon tetrachloride in the presence of amines have been reviewed44 and it has been shown45 that this type of reaction does not occurwithdiphosphines.lt was, however, successful with a phosphonite and tosylamine (Scheme 3).46 The same product was also obtained with tosyl azide. 

The Reformatsky type of reaction with Zn(0) was performed in situ and led to somewhat unstable phosphonodiamidite (step a) which was coupled with 5 -DMTr-thymidine to give the intermediate mononucleoside phospho-noamidite (step b). The latter was further coupled with 3 -acetyl-thymidine (step c). Couplings described in steps b and c were activated by tetrazole. The intermediate dinucleoside phosphonite was oxidized with (lS)-(+)-(10-camphorsulphonyl)oxaziridine (step d) or sulfurized with Beaucage reagent. The phosphonoamidites mentioned above were used in the solid-phase chemical synthesis of phosphonoacetate and thiophosphonoacetate oligonucleotides. 

The ligand properties of the related phosphonites P(OR)2R and phosphinites P(OR)R2 have attracted little attention.199,200 Reaction with silver chloride generally produced 1 1 complexes of the type AgCIL, whilst with silver nitrate, complex cations of the type AgL4 were generated. The products were characterized by elemental analysis, 7H and 31P NMR spectroscopy and conductivity measurements. 

The planar phosphite complexes [PdX2 P(OR)3 2] have been prepared by a variety of methods, such as the reaction of P(OR)3 with [PdX p in ethanol in the presence of LiX.88 The palladium(II) iodide and P(0-o-tolyl)3 complexes have trans structures or are cisftrans mixtures, but the others are predominantly cis isomers. The phosphonites, P(OR)2Ph, and... 

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