Phosphinates from phosphorus esters

Hydroformylation - [CARBON MONOXIDE] (Vol 5) - [OXO PROCESS] (Vol 17) -of allyl alcohol [ALLYL ALCOHOL AND MONOALLYL DERIVATIVES] (Vol 2) -catalysts for [CATALYSIS] (Vol 5) -C-19 dicarboxylic acids from [DICARBOXYLIC ACIDS] (Vol 8) -of ethylene [ETHYLENE] (Vol 9) -of ethylene [PROPYL ALCOHOLS - N-PROPYLALCOLHOL] (Vol 20) -of maleate and fumarate esters [MALEIC ANHYDRIDE, MALEIC ACID AND FUMARIC ACID] (Vol 15) -phosphine catalyst [PHOSPHORUS COMPOUNDS] (Vol 18) -platinum-group metal catalysts for [PLATINUM-GROUP METALS] (Vol 19) -rhodium catalysis [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -ruthenium cmpds or catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -use of coordination compounds [COORDINATION COMPOUNDS] (Vol 7)... 

In principle, lanthanide complexes of alkyl- (phosphinates) or alkoxy- (phosphonate esters) DOTP derivatives may give rise to 32 stereoisomers, existing as 16 enantiomeric pairs, which are indistinguishable by NMR spectroscopy. The isomers originate from chiral elements inherent in these complexes, including the R or S configuration at each phosphorus and the helicity defined by the pendant arm orientations (AIA). Various Ln3+ complexes of phosphinate and phosphonate ester ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) have been described in the literature [104-107]. 

If a nucleophilic addition at a carbonyl or imine carbon occurs, the product is still a phosphinate (from a phosphonous ester) or a phosphine oxide (from a phosphinous ester), but the reaction is commonly referred to as an Abramov or Pudovik reaction. An example of the Pudovik reaction is shown below (equation 16). Addition of the phosphorus nucleophile to the /3-carbon atom of an a, /3-unsaturated substrate (Michael addition) is commonly referred to as a hydrophosphinylation reaction. ... 

Reports of nucleophilic attack at atoms other than those above have also appeared. A kinetic study has compared the effectiveness of tertiary phosphines and phosphite esters in the catalysis of the cleavage of the silicon-silicon bond of methylchlorodisilanes, providing evidence for the involvement of a stabilised silylene intermediate. The anion of the y-phosphino-p-diketimine (197) has been shown to react with arsenic trichloride to give the phosphino-arsino-p-diketimine (198), in which there is a coordinative link from phosphorus to arsenic. ... 

We turn now to the comparison of phosphate esters with esters of other phosphorus oxyacids, namely phosphites, phosphonates and phos-phinates. Phosphites are distinguished from phosphates by a lower formal valence number (l.t. by a basically different bonding structure), whereas in phosphonates and phosphinates the phosphorus is formally pentavalent, as in phosphates. Phosphonates and phosphinates have direct carbon-phosphorus bonding, while the linkage of the organic groups in the phosphate esters is all of the carbon-oxygen-phosphorus type. 

The formation of equal amounts of methyl chloride and (78) from phosphorus pentachloride and bis(hydroxymethyl)phosphinic acid has been rationalized (Scheme 13) in terms of the intermediate methyl ester (79). ... 

In the simplest form of the Abramov reaction, the phosphorus-containing reactant is hypophosphorous acid (phosphinic acid) or an ester thereof, and in the reactions between the acid and formaldehyde or benzaldehyde the initial product is the phosphinic acid 144 (R = H or Ph.). However, the reaction can proceed further to give the bis(l-hydroxyalkyl)phosphinic acid (145 R = H or Ph) the latter (R = Ph) reacts readily with yet more benzaldehyde to give its benzylidene derivative, 5-hydroxy-2,4,6-triphenyl-1,3,5-dioxaphosphorinane 5-oxide (146 R = Ph). When acted on by a second mole of cyclohexanone in the presence of acetyl chloride, (l-hydroxycyclohexyl)phosphinic acid (147) gives the novel phosphinic chloride 148, characterized as the free acid 149 following ready hydrolysis A reaction between a phosphinic acid (150) and a second (non-identical) carbonyl compound leads to an unsymmetrical phosphinic acid (151). Esters of symmetrical 1, r-dihydroxy-substituted phosphinic acids are preparable from hypophosphite esters, H2P(0)0R ". ... 

The Michael-Arbuzov rearrangement is a basic reaction for the preparation of 4-coordinate species including phosphine oxides from 3-coordinate phosphorus esters, such as phosphinous esters. In most cases, the reaction requires a prolonged heating above 100 °C. Odinets et al. have now succeeded in carr5nng out the Arbuzov-reaction of ethyl diphenylphosphinite with a variety of alkyl halides in ionic liquids at or below 110 °C in short reaction times, mostly within half an hour. The best ionic liquid was l-hexyl-3-methylimidazolium bromide (Scheme 2). The recovered [hmim]Br could be recycled at least five times without a decrease in activity. 

The non-equivalence of the ester protons in the monomethyl- and monophenyl-phosphinic ester function, as in (44, Ch = chalkogen), has been studied. Compounds of type (45) have some interesting stereochemistry. They are prepared from racemic secondary butyl alcohol, and the presence of three signals in the P n.m.r. spectrum confirms that the phosphorus atom is the centre of pseudo-asymmetry. A 1 2 1 triplet is observed which is attributed to the presence of equal amounts of two mesa forms, (45) and (46), which have different values of Sp (outer peaks), and two racemic forms, (47) and (48), which have identical values of 8p (central peak). 

The Mitsunobu phosphonate coupling has been adapted to the solid-phase synthesis of peptidyl phosphonates as well.1 2 In this environment, with excess phosphonate, even the more hindered, p-branched esters are formed efficiently. A series of phosphonate tripeptides have been synthesized and used to identify novel thermolysin inhibitors from a small library. (A number of other solid-phase syntheses of phosphonamidate-, 831 phosphonate-, 79 84 and phosphinate-peptides185,86 have been described however, in these instances the phosphorus bond forming steps were performed in solution, prior to solid-phase coupling.)... 

The most common method for the synthesis of phosphinopeptides is the addition of a nucleophilic, trivalent phosphorus species to a carbon electrophile, including conjugated double bonds, alkylating agents, imines, and carbonyl compounds. By analogy with the phosphite ester additions described above, the nucleophilic form of a phosphinic acid is the trivalent species, generated from the more stable, pentavalent PH derivative by deprotonation or by silylation (cf. Scheme 2). 

The latter anomalous" behaviour has been ascribed to the direct formation of pentacoordinated products from P(III) and the substrate as distinct from nucleophilic displacement by phosphorus so that the stability of the T.S. leading to the pentacoordinated molecule dictates the rate. >11 >LI There is no doubt that several reactions which display the anomalous rate sequence (eg with peroxides, sulphenate esters and dithietenes) do give pentacoordinated products and the proposal is given further support by the reaction of diethyl peroxide with a series of cyclic phosphines in which the rate sequence parallels the stability of the P(V) products.II Furthermore, under the appropriate conditions pentacoordinated products are also formed from alkenes (eqn. 2) and alkynesl . (eqn. 3) and although rate data is only available for... 

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