Sodium/liquid ammonia cleavage

Sodium-liquid ammonia cleavage of the dimeric base dehydrothali-carpine (21a) yielded 2,10-dimethoxyoxoaporphine (21) [CxgHigOaN mp 218-220° (CH3COCH3) (53)] as a minor product (53). The IR spectrum (Nujol) of 21a shows a conjugated carbonyl peak at 1661 cm and the NMR spectrum (CDCI3) shows two methoxyl groups superimposed at 8 3.96. 

Other procedures include zinc-dust distillation, not generally useful except for exhaustive degradation of phenols to hydrocarbons, and various sodium and liquid ammonia cleavages of phenol ethers.3-7 These latter reactions lack generality and are often unpredictable. They require conditions too harsh for... 

Application of this reaction to 2, 2-anhydrouridine (LXXXVII) led to a 3-substituted nucleoside (CIV) which, upon acylation followed by reduction with Raney nickel, yielded 3-deoxyuridine (CV, R = uracilyl). Reductive cleavage of CV, by the sodium-liquid ammonia procedure,72 afforded 3-deoxy-D-en/fAro-pentose ( 3-deoxy-D-ribose ), a result which establishes position 3 as the site originally containing the ethylthio function. The authors suggest,248 as a plausible route to CIV, the initial formation of the anion CII, followed by formation of the 2,3-anhydride structure. The anhydride (CIII) is then attacked, at C3, by the ethanethiol ion, to yield... 

The constitution of hernandezine was conclusively established as XCVI by reexamination of the sodium in liquid ammonia cleavage of the alkaloid, and isolation of a nonphenolic product which was shown to be the trimethoxybenzylisoquinoline XCVIII. Evidently the methoxyl group at C-6 was eliminated during the reaction. In line with this result, sodium in liquid ammonia cleavage of 0-methylthalifendlerine (XCIX) was found to yield the same trimethoxy base XCVIII. 

The intramolecular cyclopropanation from (24) to (25), followed by regioselective reductive cleavage of (25) to (26) in the presence of sodium-liquid ammonia has featured in a new synthesis of... 

D-( — )-Armepavine and l-( -t )-armepavine have been obtained by reductive cleavage with sodium-liquid ammonia of a number of bis-benzylisoquinoline alkaloids (11, 12). A similar treatment of the pro-aporphine alkaloid pronuciferine has produced d-( — )-armepavine, a method which permits the correlation of its configuration with the aporphine alkaloids (79). 

Thiophenethiols are prepared by reduction of the sulfonyl chlorides or, more conveniently, by the reaction of Grignard rea-gents or thienyllithium compounds with sulfur. They have also been obtained by cleavage or thienyl alkyl sulfides with sodium in liquid ammonia. 3-Thiophenethiol is a by-product in the commercial thiophene synthesis. Thiophenethiols have recently also been prepared by a synthesis involving Friedel-Crafts reaction of 2,4-dinitrobenzenesulfenyl chloride with thiophenes, followed by basic cleavage of the resulting sulfide. ... 

Truce also examined a few examples of the cleavage of sulphones with sodium in liquid ammonia97 and found essentially similar results except that diaryl sulphones were reduced to sulphinate salts instead of to arylthiolates as with the lithium reductions. Dialkyl sulphones were unreactive towards sodium in liquid ammonia. 

The benzyl group can serve as a hydroxy-protecting group if acidic conditions for ether cleavage cannot be tolerated. The benzyl C—O bond is cleaved by catalytic hydrogenolysis,176 or by electron-transfer reduction using sodium in liquid ammonia or... 

For preparative purposes, titanium metal can be used in place of sodium or lithium in liquid ammonia for both the vinyl phosphate231 and aryl phosphate232 cleavages. The titanium metal is generated in situ from TiCl3 by reduction with potassium metal in tetrahydrofuran. 

On treatment with aerated sodium in liquid ammonia, tetrahydroproto-berberine JV-oxides (35a and 35b) afforded the C-14—N bond cleavage products 36 and 37 (Scheme 8) (37). The same trans IV-oxides also gave the C-14—N cleavage products 38 and 39 on photolysis (33). 

Formation of asphaltenes during solubilization of low-rank bituminous coals has been attributed to cleavage of open ether-bridges (6). But while the presence of such configurations in high- and medium-rank bituminous coals is well established (7), their existence in less mature coals remains to be demonstrated. From reactions of low-rank bituminous coals with sodium in liquid ammonia or potassium in tetrahydrofuran, it has, in fact, been concluded that open ether-bonds are absent (8) or only present in negligible concentrations (9). 

Detailed discussion of these findings will be presented elsewhere. Here we only wish to point out that responses to a hydrogen donor tend to be critically affected by minor structural differences between the compounds. Thus, while diphenyl ether remains substantially unaffected by the donor, its hydroxy-derivatives (phenoxy phenols) often display fairly high reactivity. Taken in conjunction with the failure of low-rank coals (7) and phenoxy phenols (10) to suffer reductive cleavage when treated with sodium in liquid ammonia, this lends some support for the existence of phenoxy phenol entities in low rank coals. 

Benzyl-6-methylcyclohexanone has been prepared by the hydrogenation of 2-benzylidene-6-methylcyclohexanone over a platinum or nickel catalyst, and by the alkylation of the sodium enolate of 2-formyl-6-methylcyclohexanone with benzyl iodide followed by cleavage of the formyl group with aqueous base. The 2,6-isomer was also obtained as a minor product (about 10% of the monoalkylated product) along with the major product, 2-benzyl-2-methylcyclohexanone by successive treatment of 2-methylcyclohexanone with sodium amide and then with benzyl chloride or benzyl bromide. Reaction of the sodium enolate of 2-formyl-6-methylcyclohexanone with potassium amide in liquid ammonia formed the corresponding dianion which was first treated with 1 equiv. of benzyl chloride and then deformylated with aqueous base to form 2-benzyl-2-methylcyclohexanone.i ... 

Vinyl ethers were reductively cleaved by lithium, sodium or potassium in liquid ammonia especially in the absence of alcohols (except terf-butyl alcohol) A mixture of l-methoxy-1,3- and l-methoxy-l,4-cyclohexadiene gave in this way first methoxycyclohexene and, on further reduction, cyclohexene Reductive cleavage of a-alkoxytetrahydrofurans and pyrans will be discussed in the chapter on acetals (p. 104). 

Cleavage of a benzyloxy bond was also accomplished by treatment with sodium in liquid ammonia [640] or by refluxing with sodium and butyl alcohol [641]. On the other hand, aluminum amalgams reduced a nitro group but did not cleave benzyl ether bond in dibenzylether of 2-nitrohydroquinone [642]. 

Reductive cleavage of 1,3-dithiolanes is accomplished in low yields with sodium in liquid ammonia and gives either dithiols or mercapto sulfides depending on substituents in position two [679]. 

Cleavage of substituted diphenyl ethers with sodium in liquid ammonia. 

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