Adams catalyst acetals

Cyanohydrin (52b 5 g mp 160-164°) is dissolved in acetic acid (200 ml) and placed in a 2-liter hydrogenation flask. Adams catalyst (0.75 g) is added (for 100 g cyanohydrin use 7.5 gof catalyst) and the mixture is hydrogenated until the theoretical amount of hydrogen is taken up (477 ml). The catalyst is removed by filtration, the filtrate is transferred to a 600 ml beaker provided with a stirrer and thermometer, treated with water (20 ml) and cooled to 0° (ice-salt). A solution of sodium nitrite (10 g) in water (30 ml) is added dropwise with stirring at 0°. The reaction mixture is then stirred for additional 2 hr at room temperature, treated with water (100 ml) and, after standing overnight, the precipitate is collected by filtration. The product is dissolved in ether (50 ml), the ether solution is washed sequentially... 

Support for this suggestion comes from many quarters. Reduction of the jS-carboline anhydro-bases with sodium and alcohol or with tin and hydrochloric acid gives the 1,2,3,4-tetrahydro derivatives, as does catalytic reduction over platinum oxide in an alkaline medium. On the other hand, catalytic reduction with platinum oxide in acetic acid results in the formation of the 5,6,7,8-tetrahydro-j3-carbolinium derivatives (see Section III,A,2,a). It should be noted, however, that reduction of pyrido[l,2-6]indazole, in which the dipolar structure 211 is the main contributor to the resonance hybrid, could not be effected with hydrogen in the presence of Adams catalyst. 

Condensation of 2-quinolinecarboxaldehyde 98 with acetylacetone or ethyl acetate gave the acrylate derivatives 99 and 100, respectively. Cyclization of 99 with AC2O afforded the benzindolizine 101 (80ACSA(B)79). Reduction of 100 in presence of Adams catalyst followed by hydrolysis gave 102 (78PJC107) (Scheme 19). 

Reflux 6.9 g triphenylphosphine and 6.6 g lauryl bromide (or equimolar amount of homolog) in 40 ml xylene for 60 hours. Remove solvent and wash residue with 5X20 ml ether (by decanting) to get 11 g lauryl triphenylphosphonium bromide (I). To a stirred suspension of 5.6 g (0.011M)(I) in 50 ml ether add 0.01M butyllithium solution (see Organic Reactions 8,258(1954) for preparation). Stir Vz hour at room temperature and slowly add 1.66 g 3,5-dimethoxybenzaldehyde (preparation given elsewhere here) in 10 ml ether over Vi hour. After 15 hours, filter, wash filtrate with water and dry, evaporate in vacuum. Dilute residue with pentane, filter and remove solvent. Dissolve the residual oil in 25 ml ethyl acetate and hydrogenate over O.lg Adams catalyst at one atmosphere and room temperature for 2 hours. Filter and evaporate in vacuum to get the 5-alkylresorcinol dimethyl ether which can be reciystallized from pentane and demethylated as described elsewhere here. 

Nitraramine and A-hydroxynitraramine were isolated from Nitraria schoberi (194,195). There are active hydrogen absorption bands in the IR spectrum of nitraramine at 3280 and 3530 cm- and a low intensity band at 1660 cm" (double bond). Acetylation of nitraramine (171) gave A-acetyl and A,0-diacetyl derivatives. Hydrogenation over Adams catalyst in acetic acid gave di-hydronitraramine (172) and dihydrodesoxynitraramine (173) (Scheme 30). The presence of peaks typical for quinolizidine alkaloids in the mass spectra of 171-... 

The reduction of dibenz[6,e]azepine-5,ll-dione has been studied intensively (65CCC445). Clemmensen reduction, or reduction over palladium in acetic acid, yields the -ll//-5-one, whereas reduction over Adams catalyst furnishes the ll-hydroxy-5-one. Sodium in butanol effects reduction to a mixture of the -ll//-5-one and its 7,8,9,10-tetrahydro derivative. 

In fine chemical manufacturing, the application of promoted platinum catalysts is less known. Maxted and Akhar have reported that the addition of stannous, manganous, ceric and ferric chloride to platinum oxide (Adams catalyst) facilitates the hydrogenation of aldehydes, ketones and olefins (ref. 1). The selective hydrogenation of unsaturated aldehydes or ketones to unsaturated alcohols has been achieved by the addition of ferrous sulfate and zinc acetate to platinum catalysts (ref. 2). 

An important advance was made when it was observed that photolysis of the (3-enamido ketone 165, which was readily available from the indoline 163 by Birch reduction followed by N-aryloylation, delivered the lactam 168 as the only photoproduct (Scheme 17) (125). Reduction of 168 with LiAlH4 gave ( )-a-anhydrodihydrocaranine (143), which was then converted to ( )--y-lycorane (93) on hydrogenation over Adams catalyst in acetic acid. In a similar fashion, irradiation of the bromo or iodo enaminones 166 (Z = Br, I), which were obtained by alkylation of the intermediate imino ether formed on Birch reduction of 163, afforded a mixture (approximately 3 2) of the lactam 168 together with the photoreduction product 167 (126). 

The main problem here is removing the phenyl ester groups from the phosphonic moiety.We have found that convenient routes for deblocking are hydrogenation on Adams catalyst and transesterification methods followed by hydrogen bromide in glacial acetic acid treatment. The best results ewre obtained if transesterification was carried out using potassium fluoride-crown ether-methanol system. 

The product of step 2 (17 g) was dissolved in glacial acetic acid and hydrogenated in the presence of Adams catalyst until hydrogen uptake had ceased. The catalyst was filtered off through a keiselguhr filter and the filtrate was evaporated to leave 13.0 g of almost colorless solid. The mass and NMR spectra confirmed the structure of product. 

XLIII) the IR-spectrum of its iodide is also similar to that of sempervirine iodide and further shows the absence of a vinyl group. Catalytic hydrogenation of melinonine G over Adams catalyst in aqueous alkaline solution gives an indole which yields propionic and acetic acids on modified Kuhn-Roth oxidation and which, therefore, contains a C-ethyl group. All this evidence is accommodated in structure XLIV for melinonine G the indolic reduction product must then have structure... 

The brown platinum oxide Pt02-H20, the Adams catalyst, when treated with H2 gives a very finely divided black suspension of metal. The reagent is used in acetic acid or ethanol for the hydrogenation of alkenes. 

The aromaticity of the imidazole nucleus ensures stability towards reduction, and when benzimidazole (27) is hydrogenated over Adams catalyst in acetic acid the carbocyclic ring is reduced first to give the tetrahydrobenzimidazole (28). However, if the solvent is changed to acetic anhydride, A(-acylation promotes the reduction of the heterocycle and the 1,3-diacetylbenzimidazoline (29) is then formed (Scheme 1). Imidazole (30) under these conditions gives 1,3-diacetylimidazoline (31). Imidazolium salts (32) are easily reduced and treatment with excess sodium borohydride in 95% aqueous ethanol culminates in the formation of 1,2-diamines, (33) or (34). Either N—C bond may cleave, although if the substituent R is benzyl the major products are benzylamines (33 R = Bn). ... 

Hydrogenation of heterocyclic enamines of the alkaloid series can be accomplished either in acetic acid using Adams catalyst or, better, with amalgamated Zinc (Scheme 129). 

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