Phenols reductive deoxygenation

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

Fig (14) Olefin (107) has been converted to cyclic ether (114) by standard reactions. Its transformation to enone (115) is accomplished by annelation with methyl vinyl ketone and heating the resulting diketone with sodium hydride in dimethoxyethane. The ketoester (116) is subjected to Grignard reaction with methyllithium, aromatization and methylation to obtain the cyclic ether (117). Its transformation to phenolic ester (119) has been achieved by reduction, oxidation and esterification and deoxygenation. 

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 synthetic potential of reductions by formate has been extended considerably by the use of ammonium formate with transition metal catalysts like palladium and rhodium. This forms a safe alternative to use of hydrogen. In this fashion it is possible to reduce hydrazones to hydrazines, azides and nitro groups to amines, to dehalogenate chloro-substituted aromatics, and to carry out various reductive removals of functional groups. For example, phenol triflates are selectively deoxygenated to the aromatic derivatives using triethylammonium formate as reductant and a palladium catalyst. - These recent af li-cations have been reviewed. 

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. 

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%. 

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

Best and Wege59have reported the first total synthesis of Mansonone F and this is described in Scheme 10. Phenol (111)60 was made to react with 2-chloroacetyl-5-methylfuran (112) in dimethylsulfoxide and sodium methoxide to yield (113). Ketalization of (113) followed by catalytic reduction and basic hydrolysis afforded anthranilic acid (114). Diazotization followed by pyrolysis with propene oxide in 1,2-dichloroethane probably yielded aryne (115), which undergoes intramolecular Diels-Alder reaction producing the adduct (116). Deoxygenation and then acid hydrolysis afforded the product (117). This was subjected to Grignard reaction. The resulting tertiary alcohol on nitration yielded the nitro compound (118) which was subjected to reduction and oxidation respectively to obtain (119). It yielded Mansonone F (120) on dehydration. 

Scheme 10 Phenol (111) was converted to compound (113), whose transformation to anthranilic acid (114) was achieved by standard organic reactions. Its conversion to adduct (117) was accomplished by subjection to four successive reactions (a) diazotization, (b) pyrolysis, (c) deoxygenation, (d) acid hydrolysis. This yielded nitro compound (118) by Grignard reaction, followed by nitration. Reduction of (118) and then oxidation of the resulting compound produced compound (119), which on dehydration afforded Mansonone F (120)...

Given that biomass can be converted to a liquid product that is primarily phenolic, then oxygen removal and molecular weight reduction are necessary to produce usable hydrocarbon fuels. Upgrading biomass-derived oils differs from processing petroleum fractions or coal liquids because of the importance of deoxygenation. This topic has received only limited attention in the literature (6-11). 

---