Phosphoramidate anions

The reaction between phosphoramidate anions and C02, resulting in P—N bond fission, was first reported in the early 1960s the fate of the phosphorus-containing moiety was not described clearly, nor were any conclusions reached as to the stereochemistry of the reaction. The reaction of the anions (96) and (97) with C02 and CS2... 

Having established a very effective method for the synthesis of tricar-bonyl(T74-vinylketene)iron(0) complexes, Thomas has subsequently undertaken the most comprehensive study on the reactivity of these complexes to date. The reactions of 221 with phosphoramidate anions,90134 coordinating ligands such as phosphines3 and isonitriles,69,87,89,135,142,143 a variety of nucleophiles,86,89135142 phosphonoacetate anions,88,89 alkynes,108,109,144,145 and al-kenes146,147 have ah been investigated. Crucially, Thomas has also developed a method138 for the kinetic resolution of the vinylketene complexes (221) that ultimately yields enantiomerically pure samples of the complex. This... 

Let us first consider the reaction between vinylketene complexes and phosphoramidate anions.90,134 Deprotonation of the appropriate phos-phoramidate with Bu"Li affords the corresponding phosphoramidate anion (232.a-232.c), which undergoes a Wadsworth-Emmons type reaction on the ketene carbonyl to afford the ketenimine complexes 233. Ketenimine complexes may also be prepared by the thermolysis of the vinylketene complexes (221) with isonitriles (vide infra).69... 

Having explored the scope of this reaction, it was then possible to use an optically active phosphoramidate (232.d), derived from (5)-a-methyl-benzylamine, to perform a kinetic resolution procedure.134,138 Upon reaction of 221 with 0.5 equiv of the phosphoramidate anion 232.d, selective reaction with the 7 -isomer of 221 resulted in an enhancement in the proportion of 5-221 along with the expected ketenimine products (233). The absolute configuration of i -233.d was determined by X-ray crystallography, and thus all other absolute configurations assigned by comparison of CD and HPLC data.39,138... 

Phosphoramidate anion also reacts with isocyanates to give carbodiimides [40, 41]. However, the procedure is limited by the tendency of many isocyanates, especially the striaght-chained aliphatic ones, to polymerize in the basic medium [42]. 

In the palladium-catalyzed allylic amination reaction, primary and secondary amines can be used as nucleophiles, whereas ammonia does not react. Therefore, many ammonia synthons have been developed, and a variety of protected primary allyl amines can now be prepared using azide, sulphonamide, phthalimide, di-f-butyl iminocarbonate ((Boc)2NLi), and dialkyl A-(rerr-butoxycarbonyl)phosphoramide anions as the nucleophile [20], An example of the use of ((Boc)2NLi) 30 as the amine nucleophile in the palladium-catalyzed allylic amination reaction is shown in Eq. (9). This reaction also illustrates the problem with the regioselectivity in the reaction as a mixture of the products 31-33 are obtained [21]. 

Presumably, this transformation proceeds via initial protonation of divinylketone 49 by phosphoramide 50, resulting in the formation of adduct 53, which consists of a cyclopentadienyl cation and a phosphoramide anion. Subsequent conrotatory 4n electrocyclization leads to an oxyal-lyl cation 54 that, through the elimination of a proton, forms 55. Subsequent protonation results in the formation of cyclopentenone 51 or 52, regenerating Br0nsted acid catalyst 50 (Figure 8). 

Diethyl N-cyclohexylphosphoramidate allowed to react with NaH in 1,2-di-methoxyethane, and phenyl isocyanate added to the resulting phosphoramidate anion N-phenyl-N -cyclohexylcarbodiimide. Y 60%.— Phosphoramidates, which are readily available, provide convenient laboratory procedures for the prepn. of unsatd. nitrogen compounds such as imines, ketenimines, isocyanates, or isothiocyanates. F. reactions s. W. S. Wadsworth, Jr., and W. D. Emmons, Am. Soc. 64, 1316 (1962). 

The hydrolysis of triamido-, diamido-, and monoamido-phosphoric acid has been studied. The triamido-compound reacts by both acid- and base-catalysed mechanisms, and also exhibits spontaneous hydrolysis in the pH range 7—8. The diamido-and monoamido-compounds react by an acid-catalysed pathway, though the dependence of rate upon pH is complicated by zwitterion formation. The reaction of A-(4-chlorophenyl)phosphoramidate anion, [ArNHPOsH]-, in hydroxylamine buffers involves a common intermediate for hydrolysis and hydroxylaminolysis. This is described as a solvated dipole pair, derived from a zwitterion ... 

Phosphoramidate anions 52 also react with carbon dioxide to give carbamates 53, which on heating to 80 °C afford isocyanates in good yield ". ... 

In the reaction of the phenyl phosphoramidate anion 53 (R = Ph) with carbon dioxide only triphenyl isocyanurate is obtained because the generated phenyl isocyanate trimerizes under the reaction conditions. Also, from sodium diethyl A -alkoxy-phosphoramidate (R = OR) and carbon dioxide only 1,3,5-trialkoxyisocyanurates are obtained . 

The reaction of carbon disulfide with iminophosphoranes is quite general. In addition to trialkyl- and triaryliminophosphoranes also bisalkoxyalkyliminophosphoranes, trialkoxyiminophosphoranes , dimeric trichlorophosphazenes and phosphoramidate anions react similarly. Bisiminophosphoranes react with carbon disulfide to give diisothiocyanates which are used in the construction of macrocyclic carbodiimides". ... 

The decomposition of urethanes either thermally or in the presence of phosphorus pentachloride has been reported. An interesting new reaction involves the decomposition of phosphoramidate anions. 

A series of N-allyl sulfamates, phosphoramides, and phosphorimidates was prepared to explore the possibility of O- N rearrangements via the intermediacy of the contact alkene radical cation/anion pair, followed by 5-exo-trigonal radical cyclizations (Fig. 4) [142],... 

The preparation of novel phase transfer catalysts and their application in solving synthetic problems are well documented(l). Compounds such as quaternary ammonium and phosphonium salts, phosphoramides, crown ethers, cryptands, and open-chain polyethers promote a variety of anionic reactions. These include alkylations(2), carbene reactions (3), ylide reactions(4), epoxidations(S), polymerizations(6), reductions(7), oxidations(8), eliminations(9), and displacement reactions(10) to name only a few. The unique activity of a particular catalyst rests in its ability to transport the ion across a phase boundary. This boundary is normally one which separates two immiscible liquids in a biphasic liquid-liquid reaction system. 

Two patterns are possible in the activation mechanism by simple chiral Lewis base catalysts. One is through the activation of nucleophiles such as aUyltrichlorosilanes or ketene trichlorosilyl acetals via hypervalent silicate formation using organic Lewis bases such as chiral phosphoramides or A-oxides. " In this case, catalysts are pure organic compounds (see Chapter 11). The other is through the activation of nucleophiles by anionic Lewis base conjugated to metals. In this case, transmetal-lation is the key for the nucleophile activation. This type of asymmetric catalysis is the main focus of this section. 

Savignac, P. Leroux, F. Normant, H. Carb-anions-a phosphoramides. II. Formation, stabilite et utilisation en synfhese des carb-anions derivant de N-methyl N-benzylphos-phoramides. Tetrahedron 1975, 31, 877-884. 

Preparation of phenyl-substituted silyl anion is a simple process either from chlorosilanes or disilanes (equation 15). Trimethylsilyl anions can he prepared from hexamethyldisi-lane by reaction with RM (RM=MeONa, MeLi ) in a strongly basic solvent such as HMPA (hexamethyl phosphoramide). 

Hydrolysis of phosphoramidic acid (NH2-P03H2) has been studied " in the acidity range pH 2-8, in aqueous solution and in some mixed solvents. Reaction appears to occur through the mono-anion, the neutral molecule and through a protonated species (rate equation (1) and Table 13). 

RATE COEFFICIENTS FOR REACTION OF THE MONO-ANION OF PHOSPHORAMIDIC ACID WITH VARIOUS BASES AT 25 °C ... 

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