Diethyl benzylphosphonate

Scheme 2.18 gives some representative olefination reactions of phosphonate anions. Entry 1 represents a typical preparative procedure. Entry 2 involves formation of a 2,4-dienoate ester using an a, 3-unsaturated aldehyde. Diethyl benzylphosphonate can be used in the Wadsworth-Emmons reaction, as illustrated by Entry 3. Entries 4 to 6 show other anion-stabilizing groups. Intramolecular reactions can be used to prepare cycloalkenes.264... 

We similarly prepared diethyl benzylphosphonate, C6H5CH2PO(OEt)2 (IV), using benzyl chloride in place of bromofluoroethane. 

In passing, it may be noted that we prepared diethyl 2-fluoroethylphosphonate (III) and diethyl benzylphosphonate (IV) by an alternative route from sodium diethyl phosphite and the corresponding halides.6... 

Aguila, A. O Shea, E. Kamat, P. V. Radiolytic reduction and oxidation of diethyl benzylphosphonate. A pulse radiolysis study, Advance Oxidation Technology 1998, in press. 

Allow the reaction mixture to cool, set up the distillation unit and then distil under reduced pressure6 to afford the desired diethyl benzylphosphonate (b.p. 106-109°C/1 mmHg) as a colourless liquid (quantitative). 

Diethyl benzylphosphonate can be used without distillation. However, a lower yield in subsequent... 

When the halogen compound employed in the first step has an activated halogen atom (RCH CHCHjX, QHjCHjX, XCH2CO2H) a simpler procedure known as the Horner phosphonate modification of the Wittig reaction is applicable. When benzyl chloride is heated with triethyl phosphite, ethyl chloride is eliminated from the initially formed phosphonium chloride with the production of diethyl benzylphosphonate. This phospho-... 

However, the acidities of the benzyltriphenylphosphonium cation (pATa = 17.4) and of diethyl benzylphosphonate (pATa = 27.6) are sufficiently different to throw into question the likelihood of deprotonation of diethyl benzylphosphonate by the radical anion of 1. On the basis of a detailed study of the processes associated with the reduction of 1 (discussed later), it is likely that the effective base may well be the much more basic triphenylmethyl-derived carbanion, 4 in Scheme 20 (pATa of PI13CH = 30.6). This may possibly be produced by adventitious protonation of the fuchsone radical anion. Alternatively, the active EGB may be the dianion formed by disproportionation. 

While the diethyl benzylphosphonate anion did not react with phenyloxirane, even though the anion was prepared in situ, the diethyl cyanomethylphosphonate anion gave 2-phenylcy-clopropane carbonitrile in 51% yield. ... 

The reaction of diethyl alkylphosphonates with phenylsulfonyl chloride in the presence of n-BuLi (2 eq) in THF at low temperature followed by the addition of carbonyl compounds produces diethyl l-alkyl-l,2-epoxyalkylphosphonates in 30-80% yields, whereas under the same conditions, diethyl benzylphosphonates give comparable quantities of 1-phenyl-1-chloroalkenes (35-55%, Scheme 3.28). Similarly, p-iminophosphonate carbanions, obtained from diethyl 1-lithiomethylphosphonate and nitriles, react with phenylsulfonyl chloride in THF at -78°C. Hydrolysis (3 M H2SO4) of the resulting a-chloro-p-enaminophosphonates produces diethyl a-chloro-P-ketoalkylphosphonates in satisfactory yields (53-67%). ... 

Grassberger, M.A., Formylation of diethyl benzylphosphonate and (aryhnethylfphosphonium salts, Justus Liebigs Ann. Chem., 1872, 1974. 

The effect of temperature on the addition equilibrium can, for instance, be observed in the reaction of the carbanion of diethyl benzylphosphonate with 4-fluoronitrobenzene. At low temperature the addition proceeds exclusively at the position 2, and oxidation of the produced adduct affords the product of ONSH. On the other hand, at room or a higher temperature the S Ar of fluorine in the position 4 takes place [76]. Similarly, when the reaction of nitroarenes with the anion of diphenylphosphine is carried out at low temperature in liquid ammonia in the presence of KMn04 diphenyl(nitroaryl)phosphine oxides are formed, as illustrated by the ONSH in 4-fluoronitrobenzene (Scheme 16) [77]. 

Benzisoxazoles can readily be obtained by anaerobic, spontaneous transformation of carbanions of a-(ort/ o-nitroaryl)benzyl phosphonates, derived from the ONSH in nitroarenes with carbanion of diethyl benzylphosphonate, whereas oxygen oxidation of such carbanions gives nitrobenzophenones (Scheme 96) [232],... 

Benzylphosphonic acid esters. A soln. of benzyl diethyl phosphite (0.1-0.2 M) in deoxygenated benzene irradiated in a quartz tube with a 450 W medium-pressure Hg-lamp - diethyl benzylphosphonate. Y 85-95%. With chiral O-benzyl groups, reaction proceeds with complete retention of configuration at the chiral carbon, F.e.s. W.G. Bentrude et al., J. Am. Chem. Soc. 110, 6908-9 (1988) stereochemistry s.a. Tetrahedron Letters 30, 1025-8 (1989). 

Accoimt for the fact that diethyl benzylphosphonate (12) is a stronger acid than benzyltriphenylphosphonium chloride (4). 

Consider the NMR spectral data for diethyl benzylphosphonate (Fig. 18.8). Note that has 1 = 1/2 and therefore couples with neighboring hydrogen and carbon and carbon nuclei having = 1/2. 

EIomer-Wadsworth-Emmons reactions lend themselves to the use oi phase-transfer catalysis in Experiments [19B] and [19D]. Phase-transfer catalysis allows the use of an aqueous base (NaOEI in H2O) with the organic compounds dissolved in an organic solvent (hexane in Experiment [19B], methylcyclohexane in Experiment [19D]) immiscible with water. The reaction system, as the name implies, involves two phases—an aqueous phase and an organic phase. The phase-transfer catalyst plays a very important role without it, no reaction would occur, since the initial reactants (hydroxide ion and diethyl benzylphosphonate) are dissolved in different, immiscible phases, and NaOH is insoluble in hexane (or methylcyclohexane), and diethyl benzylphosphonate is insoluble in water. 

The phase-transfer catalyst is soluble in both water and the organic solvent. It is water soluble because it is an ion, and it is hexane soluble because of the three long-chain alkyl groups. Thus, the phase-transfer catalyst distributes itself in both phases, and freely shuttles back and forth through the phase boundary between solvent layers. In aqueous NaOH, the chloride anion exchanges with hydroxide anion, as the counterion to the ammonium cation. When it does this, the catalyst carries the hydroxide ion from the aqueous phase, as an ion-pair, across the phase boundary into the organic phase, where the base then reacts with the diethyl benzylphosphonate. The Homer-Wadsworth-Emmons reaction then occurs, producing the alkene and diethyl phosphate anion. This anion becomes associated with the ammonium cation of the phase-transfer catalyst and is transported to the aqueous layer, where the catalyst picks up another hydroxide ion and repeats the entire process. 

Reagents and Equipment. Weigh and place 88 mg (100 (xL) of tricapryl-methylammonium chloride (Aliquat 336) in a 10-mL round-bottom flask containing a magnetic stirrer. Add 100 pL (0.98 mmol) of benzaldehyde, 200 jxL (0.96 mmol) of diethyl benzylphosphonate, 2.0 mL of hexane, and 2 mL of 40% sodium hydroxide solution. Attach the flask to a reflux condenser. 

NOTE. The benzaldehyde, diethyl benzylphosphonate, hexane, and NaOH solution are dispensed in the hood using automatic delivery pipets. Aliquat 336 is very viscous and is best measured by weighing. A medicine dropper is used to dispense this material. It is advisable to lightly grease the bottom joint of the condenser since strong base is being used. 

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