Of enol phosphates

The monomeric phosphate ion 102 was first postulated in 1955 as an intermediate of the hydrolysis of monoesters of phosphoric acid in an aqueous medium 57,58). Another 24 years were to elapse before compound 102 was observed directly, and then not in solution but in the mass spectra of some pesticides. The negative ion Cl spectra of enol phosphates 94 and of the thiophosphorie ester 95 display an intense peak at m/e == 78.9590, which is unequivocally assigned to the POf ion 59). 

Erker and Trinkl synthesized the tricycles 177 as novel GABA-A/benzodiazepine receptor ligands via synthesis of enol phosphates such as 175 and reaction with isocyanides 176 (Scheme 13) <2001H1963>. 

Enantioselective hydrogenation of a series of enol phosphates with a Bu-Mini-Phos-Rh or a Bu-BisP -Rh catalyst provides moderate to excellent ee-values (Scheme 26.7) [99]. 

Given the large number of tandem cyclization processes that have been explored [63], it is disappointing to note that so few have been promoted electrochemi-cally. There appears to be a significant opportunity for additional exploration. Two tyiws of tandem cathodic cyclizations are discussed below. The first involves generation of a ketyl, and its subsequent cyclization onto a pendant alkene to afford a new radical that closes onto a second alkene [64,65]. The second focuses on chemistry not yet discussed involving the reductive cyclization of enol phosphates of 1,3-dicarbonyl compounds [66]. 

The opportunity for tandem cyclization was explored. Here, the results can be accommodated by postulating the intermediacy of a vinyl radical [66]. For example, the controlled potential reduction of enol phosphate 246 affords 247 as a mixture of stereoisomers, in addition to a 15% yield of the linearly fused tricyclopentanoid 248. Assuming that the initial reduction cleaves the phosphate unit, then there exists the opportunity for the resulting radical 249 to be further reduced to afford a carbanion, or undergo a 5-exo-trig radical cyclization onto the pendant alkene. Given the nature of the products and the fact that they are inconsistent with the expectations of carbanion chemistry, it seems clear that the latter pathway dominates. 

PREPARATION AND REDUCTIVE CLEAVAGE OF ENOL PHOSPHATES 5-METHYLCOPROST-3-ENE... 

For example, a wide range of a-(acyloxy)acrylates have been hydrogenated with excellent enantioselectivity using the Et-DuPhos-Rh catalyst. High selectivities are also obtained for the asymmetric hydrogenation of the B/Z-isomeric mixtures of yS-substituted derivatives (Eq. 12). Asymmetric hydrogenation of enol phosphates with either Du-Phos-Rh or BPE-Rh catalyst provides moderate to excellent enantioselectivity (Eq. 13)... 

The present preparation illustrates a general and convenient method for a two-step deoxygenation of carbonyl compounds to olefins. Related procedures comprise the basic decomposition of p-toluenesulfonylhydrazones, the hydride reduction of enol ethers, enol acetates, enamines, the reduction of enol phosphates (and/or enol phosphorodiamidates) by lithium metal in ethylamine (or liquid ammonia),the reduction of enol phosphates by titanium metal... 

The reductive fission of enol phosphates to form olefins is a... 

PD(PPH3)4-Catalyzed Alkylation of Enol Phosphates with Trialkylalumi-num Compounds... 

Allylsilanes. A regio- and stereoselective synthesis of allylsilanes involves nickel-catalyzed coupling of enol phosphates with trimethylsilylmcthylmagnesium chloride... 

Some of the reactions of PO3- parallel enzymatic reactions promoted by adenosine triphosphate (ATP). Pyruvate kinase catalyzes the equilibration of ATP and pyruvate with adenosine diphosphate (ADP) and phosphoenol pyruvate (11,12). In a formal sense, this reaction resembles the preparations of enol phosphate (eqs. 6 and 7). Cytidine triphosphate synthetase catalyzes the reaction of uridine triphosphate with ammonia to yield cytidine triphosphate (13). In a formal sense, this reaction resembles the replacement of the ester carbonyl group of ethyl acetate by the nitrogen of aniline (eq. 8). 

The reaction of enol phosphates 84 with lithium -butyl tellurolate 85a, generated by reaction of -butyllithium with elemental tellurium, occurs rapidly to give the corresponding vinylic tellurides 86 (Scheme 51). Mixtures of (Z)- and ( )-enol phosphates afford the (Z)-vinylic telluride as the only product. ... 

Dialkyl alkynes. A recently reported route to these substances involves reductive elimination of enol phosphates of /8-oxo sulfones with sodium amalgam in DMSO-THF at 0°. 

A similar synthesis of alkynes by reductive elimination of enol phosphates of /3-oxosulfones with sodium in liquid ammonia has been reported. ... 

Deoxygenation of phenols. The reduction of enol phosphates to alkenes by titanium metal (8,482) has been extended to reduction of aryl diethyl phosphates to arenes. Yields are in the range 75-95% reduction with lithium in liquid ammonia (1, 248) usually proceeds in low yield. 

The evident importance of the rearrangement of enol phosphates leading to C-P bond formation, under biological conditions should be mentioned. The occurrence of enzymes responsible for C-P bond formation in Tetrahvmena and Streptomvces hyqroscopicus has already been established, and new systems have now been reported. 

Treatment of enolates with (R0)2P(0)C1 also results in 0-trapping to yield the corresponding enol phosphates. Dissolving metal reduction of enol phosphates is a useful procedure for the deoxygenation of ketones with concomitant, regiospecific formation of the alkene. ... 

Coupling of enol phosphates and alkylaluminum compounds.1 Enol phosphates and R3A1 couple in the presence of 3 mole % of this Pd(0) complex to give alkenes with retention of configuration. 

Perkow reaction. Formation of enol phosphates on treatment of a-halocarbonyl compounds with trialkyl phosphites. 

As might be expected, keto-sugar acetates undergo the Perkow reaction with trimethyl phosphite to give a mixture of enol phosphates (27) and (28). In other cases the products appear to be dependent on the leaving group, and the Perkow products... 

Sodium enolates of diethyl 2-oxoalkylphosphonates react with diethyl chlorophosphate to produce enol phosphates. Low-temperature treatment of enol phosphates with tert-BuOK induces the ()-elimination of potassium diethyl phosphate and formation of diethyl 1-alkynylphosphonates in good yields (43-95%, Scheme 7.113). However, the reaction is prone to prototropic isomerization and diethyl 2-oxobutyIphosphonate leads to a mixture of diethyl 1-butynyIphosphonate (43%) and diethyl 2-butynylphosphonate (51%). ... 

Lichtenthaler, F.W., The chemistry and properties of enol phosphates, Chem. Rev., 61, 607, 1961. Arbuzov, B.A., Lugovkin, B.P.. and Bogonostseva, N.P., Action of a- and y-bromoacetoacetic ester and 2-chlorocyclohexanone on triethyl phosphite and sodium diethyl phosphite, Zh. Obshch. Khim., 20, 1468, 1950 Chem. Abstr, 45. 1506a, 1951. 

There have appeared several studies on the conformation of acyclic phos-phonic and phosphinic esters and some calculations on the equilibrium conformation of a series of enol phosphates have been reported.Crystal structure determinations on the very reactive cyclic phosphate (1 R = MeO) have shown that the five-membered ring is almost planar and that the carbonyl bond is short. 

Migration of alkenyl-Pd(II) intermediates may occur during Heck reaction of enol phosphates, but it may be suppressed by using the X-Phos ligand. ... 

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