Phosphonites from phosphorus esters

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. ... 

Attack on Unsaturated Carbon.- A versatile route to phosphinic acids (15) is the 1,4-addition of bis(trimethylsilyl) phosphonite (16) to a,p-unsaturated esters.The pyrophoric (16) was prepared in s/fu from triethylammonium phosphinate silylation and 1,4-addition can be repeated to give (17), or performed in one step if symmetrical phosphinic acids (17) are wanted. Tervalent phosphorus acid esters (18) react with dialkyl acetylenedicarboxylates in the presence of carbon dioxide to give 1,2-oxa-phospholenes (19) these reacted further with an excess of the phosphorus reagent to give different ylids, (20) or (21), dependant on the number of methoxy groups in (18). 

The reaction of a phosphonamidite (79) with a trifluoracetyl ester (80), to give a phosphonite (81), has been shown to be catalysed by 4-dimethylaminopyridine. In contrast to an earlier report where a similar reaction proceeded with retention of configuration at phosphorus, the present system gave an equal amount of the two diastereomers (81). A mechanism is proposed which involves attack of an alkoxide, formed by de-trifluoracetylation of (80), on an equilibrating DMAP-intermediate (82). Another unusual substitution reaction is one between an alkoxyborane (83) and a phosphite (84). The phosphite was prepared in situ from acetylacetone and diethyl phosphorochloridite, and the substitution occurred under very mild conditions and gave high yields of phosphates after oxidation. 

Simple aliphatic aldehydes are also said to yield products which contain the equivalent of 2-3 mol of RCHO per phosphorus atom, some of which have been shown to have an oxyphosphorane structure. (For an introductory account of this fascinating area of phosphorus chemistry, the reader should consult early reviews by Ramirez . ) The phosphite ester obtained from 2-hydroxybenzaldehyde and diethyl chlorophosphite cyclizes with rearrangement to the l,2-benzoxaphosph(V)ole derivative 205 (R = H, R = EtO), and a similar process was observed in the case of phosphites and phosphonites derived from 2-hydroxyacetophenone to give 205 (R = Me) . 

The phosphobetaines can be prepared by the reaction of alkyldimethylamine with bromoalkylethylphenyl-phosphinate or bromoalkyidiethylphosphonate. The phosphorus reagents are prepared from diethylphenyl-phosphonite or triethylphosphite and a dibromalkane by an Arbusov reaction (27). Alternatively, phosphobetaines can be prepared by the reaction of an alkylamido-propyldimethylamine with a phosphoric acid ester and formaldehyde (28). 

In the case of copolymerization of vinylphosphonic acid monoethyl ester (92) with cyclic phosphonites (86), the alternating copolymer (93) having two kinds of phosphorus atoms in the main chain was formed. During the copolymerization, monomer 92 was reduced involving a hydrogen-transfer process and monomer 86 was oxidized the oxidation state of the phosphorus atom of monomer 86 changed, therefore, from trivalent to pentavalent ( oxidation-reduction copolymerization ). ... 

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