Replacement of oxygen by phosphorus

Replacement of oxygen by phosphorus by means of elemental phosphorus... 

The action of phosphorus pentasulphide on oxygen compounds generally brings about the replacement of oxygen by... 

Acetic acid phosphorus oxide chloride 2,3-Dihydrofuran ring opening with replacement of oxygen by chlorine... 

Phosphorus pentahalide Replacement of oxygen by halogen in N-heterocyclics... 

Pyridine phosphorus pentasulfide Replacement of oxygen by sulfhydryl... 

Phosphorus oxide chloride Replacement of oxygen by amino groups... 

Carius (8) replaced the oxygen in phosphoryl chloride by sulfur. This may be somewhat analogous to the replacement of oxygen in a carbonyl group by sulfur using phosphorus pentasulfide. Prinz (8) used thionyl chloride in his reaction with phosphorus sulfide and De Fazi (2) used carbon tetrachloride in a very interesting preparation of this important intermediate. 

Reductive removal of halogen substituents has been of value in the synthesis of pyrimidines and purines since the time of Fisher (1899). Natural purines were de-oxygenated in a sequence of reactions involving the replacement of hydroxyl by chlorine through the reaction with phosphorus pentachloride and the reduction using zinc dust and water [152], 2-Chloropurines 45 are not reduced under these conditions. The 2-iodopurines are however reduced by zinc and water [152]. The elec-... 

Reactions of vinyliodonium salts with nitrogen, oxygen, sulfur and phosphorus nucleophiles have been reported only sporadically and have not been examined in a systematic way. The earliest studies are qualitative, while later investigations are based on rather atypical vinyliodonium structures. Such reactions usually result in the replacement of iodobenzene by the nucleophile (equation 184). The MC pathway, a common mode of reactivity for alkynyliodonium salts, has not been documented for any vinyliodonium compound. 

As convenient routes to five- and six-membered 2-oxo-l,2-oxaphosphacyclanes 62 had been developed, replacement of oxygen atoms by sulfur under the action of an excess of phosphorus pentasulfide was suggested as the first convenient route to 2-thioxo-l,2-thiaphosphacyclanes such as 108 [98, 139-141], Such a replacement can be performed as a step-by-step process (at the first step compounds transform to 2-thio-l,2-oxaphasphocyclanes, e.g. 109) however, drastic conditions are required for an exhaustive exchange (Scheme 63). 

The replacement of oxygen in phosphonic or a phosphinic acid by sulphur or selenium renders it much easier to obtain optically active forms of a simple product possessing a chiral phosphorus centre. As early as 1911, Ephraim failed to resolve anions of the type R2P(0)0, and so concluded that the anions were structurally symmetrical. However, the presence of an atom of, for example, sulphur, creates a non-symmetrical environment around the four-coordinate phosphorus atom, and permits the isolation of optical antipodes. Enantiomeric forms of a simple thiophosphonic acid derivative were first obtained by Aaron and Miller, who resolved the monoethyl ester of ethylphosphonoth-ioic acid, Et(EtO)P(S)OH, by fractional crystallization of its salts with various alkaloids. 

An interesting topological effect is the increased terminal chlorination of fatty acids when they are adsorbed and aligned on alumina Silicon disulfide and particularly boron sulfide have been used with advantage instead of phosphorus pentasulfide to replace carbonyl oxygen by sulfur The addition of sulfur monochloride to olefins followed by reduction of the adduct with sodium sulfide provides a convenient inexpensive route to a large number of episulfides A direct conversion of ar. nitro compounds to isothiocyanates has been reported Sec. phosphines add easily to olefins under UV-irradiation Advances in peptide synthesis include the use of acyloxyphospho-nium salts prepared with hexamethylphosphoramide a simple synthesis with triphenyl phosphite , and the use 4-picolyl esters at the... 

Phosphinic acids are probably, with the phosphonic acids, the simplest phosphate bioisosteres [8]. Because of their tetrahedral geometry, phosphinic acids remain quite similar in shape and are approximately isosteric with phosphates. The main difference is the presence of two phosphorus-carbon bonds (phosphinic acids) or one phosphorus-carbon bond and a phosphoms-hydrogen bond (/f-phosphinic acids). One intrinsic character of the P-C bond is its chemical and enzymatic stability when compared to P-O or P-N bonds [9]. As a consequence, phosphinates (as well as phosphonates) are often used when hydrolysis becomes a bottleneck for the activity. The number of acidic functions but also pA a values are different between phosphate and phosphinic acids [10-12]. Indeed, the replacement of oxygen atoms by hydrogens in hypophosphorous acid slightly changed the pAa when compared to the first acidity of phosphoric acid (Fig. 1). However, the presence of an alkyl group directly bonded to the phosphoms results in an increase... 

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