Deoxygenation, of phenols

In a related approach from the same laboratory, the perfluorooctylsulfonyl tag was employed in a traceless strategy for the deoxygenation of phenols (Scheme 7.82) [94], These reactions were carried out in a toluene/acetone/water (4 4 1) solvent mixture, utilizing 5 equivalents of formic acid and potassium carbonate/[l,T-bis(diphe-nylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl2] as the catalytic system. After 20 min of irradiation, the reaction mixture was subjected to fluorous solid-phase extraction (F-S PE) to afford the desired products in high yields. This new traceless fluorous tag has also been employed in the synthesis of pyrimidines and hydantoins. 

Scheme 7.82 Fluorous phase traceless deoxygenation of phenols.

Deoxygenation of phenols. Aryl nonaflaics, readily available by reaction of phenols with this reagent and triethylamine, undergo hydrogenolysis (H., Pd/C) more rapidly and in higher yield (80-90%) than do aryl mcs> lates or tosylates. 

A traceless perfluoroalkylsulfonyl linker for the deoxygenation of phenols has been reported by Holmes. A more lightly fluorous variant has also been presented by Zhang, where microwave heating was applied to increase the speed of the reaction. The traceless tag was exemplified in syntheses of triaryl-substituted pyrimidines and hydantoins (Reaction Scheme 10). 

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. 

Deoxygenation of phenols.1 Phenols are converted into urethanes by treatment with phenyl isocyanate using benzene as solvent for both the reaction and crystallization. Hydrogenolysis in acetic acid with Pd/C as catalyst gives arenes in yields of 20-80%. The variation in yield suggests that steric effects may be important. 

Olefin synthesis from a,p-unsaturated ketones. Ireland and Pflster1 have extended the procedure of Kenner and Williams (1,248, ref. 2) for deoxygenation of phenols to conversion of a,/3-unsaturated ketones into olefins. For example, the a,)3-unsaturated ketone (1) was reduced by lithium-ammonia to give an enolate anion which reacted with diethyl phosphorochloridate to give the phosphate ester (2) in 56% yield. This ester was reduced in high yield by lithium in a mixture of ethylamine and r-butanol to the olefin (3). It is noteworthy that only one olefin is formed. Actually the conversion of (1) into (3) can be carried out in 50% yield without isolation of the diethyl enol phosphate. 

On catalytic hydrogenation, the resulting phenol ethers produce arenes. A method for the deoxygenation of phenols is based on these reactions. 

Synthetic applications of tetrazoles are deoxygenation of phenols, preparation of nitrilimines and preparation of 1,3,4-oxadiazoles by the Huisgen reaction. All these have been previously... 

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