Phosphates, 0,0-diethyl reduction

Yoneda, R., Osaki, H., Harusawa, S., and Kurihara, T., Reductive deoxygenation of a,P-unsatured ketones via cyanophosphates by lithium in liquid ammonia, Chem. Pharm. Bull., 37, 2817, 1989. Yoneda. R.. Osaki, T., Harusawa, S., and Kurihara, T., Dephosphorylation of cyano diethyl phosphates by reduction with lithium-liquid ammonia. An efficient method for conversion of carbonyl compounds into nitriles.. 1. Chem. Soc.. Perkin Trans. 1, 607, 1990. 

For deoxygenation of a phenol by conversion into the mesylate or diethyl phosphate and reduction with sodium and ammonia, see Diethyl phosphonate (both volumes). 

When saccharin is treated with diethyl phosphorothiolothionate, the 3-ethylmercapto compound is obtained, rather than the expected organophosphorus compound (77 ACS(B)460). Treatment of saccharin with phosphorus pentoxide and amines gives 3-(substituted-amino)-1,2-benzisothiazole 1,1-dioxides, via an intermediate phosphate (81ZN(B)1640). Reduction of saccharin with zinc and hydrochloric acid gives 2,3-dihydro-l,2-benzisothiazole 1,1-dioxide, the method being used to estimate saccharin in foodstuffs (75MI41701). 

Phosphate groups can also be removed by dissolving-metal reduction. Reductive removal of vinyl phosphate groups is one method for conversion of a carbonyl compound to an alkene.224 (See Section 5.7.2 for other methods.) The required vinyl phosphate esters are obtained by phosphorylation of the enolate with diethyl phospho-rochloridate or /V A /V -tetramethyldiamidophosphorochloridate.225... 

Reductive removal of oxygen from aromatic rings can also be achieved by reductive cleavage of aryl diethyl phosphate esters. 

Certain organophosphorus compounds can be used to melt-stabilize PET. Stabilizers such as 3,5-di-t-butyl-4-hydroxybenzyl diethyl phosphate (Irganox 1222) and triphenylphosphate lead to a reduction in the concentration of terminal carboxyl groups of PET, thus giving improved hydrolytic stability. 

In the electrochemical reduction of aryl diethyl phosphates, the initial one-electron addition is to the aryl ring and this is concerted with expulsion of the diethyl phosphate anion leaving an aryl radical. Further electron addition and protonation leads to the reaction product in 43-73 % yields. Examples of this electro-... 

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. 

Deoxygenation of phenols may be achieved by reduction of aryl diethyl phosphates with lithium or sodium in liquid ammonia." A recent application of the methodology is outlined in Scheme 43." The reaction works well with a variety of substituted phenols, but not with dihydric phenols or naphthols. The alternative reduction of aryl sulfonates has also been examined, but the limited solubility of these derivatives can present difficulties. 

Appropriate quenching of a reductively formed lithium enolate with a carboxylic acid anhydride, chloride, methyl chloroformate or diethyl phosphorochloridate yields the corresponding enol esters, enol carbonates or enol phosphates. These derivatives may be transformed into specific alkenes via reductive cleavage of the vinyl oxygen function, as illustrated by the example in Scheme 8. 

Despite these modifications, Ireland s original method of both vinyl phosphate formation and reduction remains the most popular. In studies on the cationic rearrangements of [4.3.2]propellanes, Smith et converted a tricyclic ketone, via the diethyl vinylphosphate derivative, into the corresponding alkene (Scheme 26). In a similar manner, Kamata et al prepared A - and A -steroids (Scheme 27) with excellent control of regiochemistry. As shown in this example, esters are susceptible to cleavage under the standard reduction conditions (Li, NHa, Bu OH, -35 C), while acetals survive. 

Sodium-Ammonia, For the reduction of a phenol to an aromatic hydrocarbon a solution of the phenol and diethyl hydrogen phosphite in carbon tetrachloride is treated with triethylamine and allowed to stand for 24 hrs. for complete separation of triethylamine hydrochloride (1). The phenol diethyl phosphate ester is collected. 

The reduction of aryl diethyl phosphates to aromatic hydrocarbons (first reported several years ago) has been investigated further and foimd to be a convenient and reasonably general procedure giving consistently high yields. Reduction of the phosphorodithioate ester (49) with zinc and acid is reported to give a mixture of phosphate and phosphinothioite esters together with some... 

Reduction of phenols [1, 252, after citation of ref. 3]. In achieving the synthesis of triptindane (11), Thompson obtained the methyl ether (8a) as an intermediate, demethylated it to (9), and effected deoxygenation to (11) by the method of Kenner and Williams consisting in reaction with diethyl phosphonate or mesyl chloride and reduction of the diethyl phosphate or the mesylate ester with sodium in liquid ammonia yields, first procedure 58% second procedure 36%. 

The sequence can also be applied to the enolate anion formed by conjugate addition of organometallic reagents to a,/8-unsaturated ketones. Thus addition of diethyl phosphorochloridate to a mixture of A4-cholestene-3-one (4) and dimethyl-copperlithium gives the diethyl enol phosphate (5) in 55% yield. Reduction of the ester gives the olefin (6) in high yield. 

The method is related to that of Fetizon for preparation of A2-steroids by lithium-ammonia reduction of diethyl enol phosphates generated from 2-bromo-3-ketones (see Triethyl phosphite, this volume). 

---