Pyrophosphite esters

Phosphite or pyrophosphite esters undergo dealkylation by protonic acids with decreasing ease in the series hydrogen halide, carboxylic acid, alcohol, or phenol. The carboxylic acid reaction (18,31,171), which stops at monodealkylation, has been utilized (141) for the synthesis of aryl esters of amino acid derivatives. 

The discovery of a reaction between aldehydes and trivalent phosphorus esters came surprisingly recently. Since the report by Arbuzov and Alimov (19) in 1951 that pyrophosphite esters and aldehydes gave addition products and the subsequent disclosure by Abramov (1) that phosphites reacted similarly, the reaction has been extended by other workers (31,113,195). The yields are often low and reaction sometimes takes an unexpected course. 

An alternative synthesis of pyrophosphite esters is by condensation of alkyl phosphorochloridites using water and triethylamine (5.323), while another way of making hypophosphoric esters is by condensation of alkyl phosphorochloridates with sodium (5.324). 

Dithiopyrophosphates of type (9.495) can be made by heating dialkyl phosphorochloridothionates with sodium carbonate in pyridine, or with diaUcyl phosphorothioate salts (9.503). Alternatively these compounds may be obtained by adding sulphur to pyrophosphite esters (9.504), or by the action of thionyl chloride on sodium dialkyl phosphite (9.505). 

S.P. solid-phase technique L.P. liquid-phase technique OPTcp pentachlorophenyl ester TEEP tetraethyl pyrophosphit OTCp trichlorophenyl ester ONp p-nitrophenyl ester ONSu N-hydroxysuccinimido ester OPFp pentafluorophenyl ester OQu 8-hydroxyquinyl ester OPy 3-hydroxy-pyridyl ester ODnp 2,4-dinitrophenyl ester DCC dicyclohexylcarbodiimide HOBn 3-hydroxy-4-oxo-3,4-dihydro-l,2,3-benzotriazin Opi JV-hy-droxypiperidine EEDQ 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline Tos p-toluenesulfonyl PTC propanetricarboxylic acid OBu tm-butyl ester Nva norvaline Aha aminohexanoic acid Om ornithine... 

Coupling, active ester Bis-(2,4-dinitrophenyl)carbonate. Chloroacetonitrile. Di(p-nitrophenyl)carbonate. 2-Ethoxypyridine-l-oxide. p-Nitrobenzyl tosylate. p-Nitrophenol. p-Nitrophenyl trifluoroacetate. Pentachlorophenol. Phenyltrimethylammonium ethoxide. Phosgene. Pyrazole. Sulfur dioxide-Dimethylformamide. Tetraethyl pyrophosphite. N,N -Thionyldiimidazole. 2,4,S-Trichlorophenol. 

The preparation of -amino phosphonic esters from aminals and dialkyl phosphites was mentioned above (page 732) tetraalkyl pyrophosphites and aminals also yield oc-amino phosphonic esters as well as amino phosphites.356... 

A variation of this type of reaction involving interaction of tetraethyl pyrophosphite with an amino acid has been employed for peptide synthesis (12). In this instance, the initial product, an acyloxy phosphite (22), is sufficiently reactive to interact with an amino acid ester to yield a peptide and diethyl phosphonate. 

The synthesis of homologues of (hydroxymethylene)bisphosphonic acid may be achieved through reactions between other carboxylic acids, PCI3 and water at 130 and the use of carboxylic esters is also feasible". (Hydroxymethylene)bisphosphonic acid and its ethers are obtainable from tetraalkyl pyrophosphites and alkyl formates in the presence of BF3 at 20-130 Yet a further reactant combination consists of an alkanoic ester, and P4O6-BF3, which produces glasses, but from which the bisphosphonic acid may be extracted with boiling dilute HCl. ... 

Tetraethyl pyrophosphite Pyrophosphoric acid esters with organic dehydrating agents... 

---