Catalytic reduction, preparation

This may be prepared by the catalytic reduction of pure diphenyl (see Section 111,150). 

By catalytic reduction of a p-unsaturated ketones, prepared from aldehydes by the Claisen - Schmidt reaction (see under Aromatic Aldehydes), for example ... 

As mentioned previously, aldehydes can be prepared by Stephen s method of reduction of nitriles by stannous chloride (37, 91). Polaro-graphic reduction of thiazolecarboxylic acids and their derivatives gives lower yields of aldehydes (58). Ozonolysis of styrylthiazoles, for example, 2-styryl-4-methylthiazole, followed by catalytic reduction gives aldehyde with 47% yield of crude product (30). 

Trifluoroethanol was first prepared by the catalytic reduction of trifluoroacetic anhydride [407-25-0] (58). Other methods iaclude the catalytic hydrogeaatioa of trifluoroacetamide [354-38-1] (59), the lithium aluminum hydride reductioa of trifluoroacetyl chloride [354-32-5] (60) or of trifluoroacetic acid or its esters (61,62), and the acetolysis of 2-chloro-l,l,l-trifluoroethane [75-88-7] followed by hydrolysis (60). More recently, the hydrogenation of... 

Manufacture. The manufacture of 1,4-cyclohexanedimethanol can be accompHshed by the catalytic reduction under pressure of dimethyl terephthalate ia a methanol solution (47,65). This glycol also may be prepared by the depolymerization and catalytic reduction of linear polyesters that have alkylene terephthalates as primary constituents. Poly(ethylene terephthalate) may be hydrogenated ia the presence of methanol under pressure and heat to give good yields of the glycol (see Polyesters) (66,67). 

Naphthalenediol. This diol can be prepared by the chemical or catalytic reduction of 1,4-naphthoquinone. Both the diol and quinone are of interest because of their relation to the vitamin K family. Carboxylation of 1,4-naphthalenediol with CO2—K2CO2 followed by neutralization gives... 

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

The isolation of the 6-deoxytetracyclines (44) led to other chemical modifications of (1). 6P-Deoxytetracycline [5614-03-9] (13), prepared by catalytic hydrogenolysis of tetracycline (1), resulting ia an iaversion (45) of the configuration at the C-6 position, but retention of antibacterial activity. Catalytic reduction (7,8) of the 6-methylene derivative (14) yields both the 6a-methyl (15) and 6P-methyl compound (13). The 6a-isomer (15) is reported (7,45) to be more active than the 6P isomer (13). The a-isomer, doxycycline (6), is an example of a semisynthetic tetracycline that has become commercially useful. 

Since ivermectin (= 22,23-dihydroavermectin B ) is obtained by catalytic reduction of avermectin B, the same procedure using tritium gas convenientiy affords tritiated ivermectin (22,23- [JT]-22,23-dihydroavermectin B ). The preparation of a tritiated derivative containing a 22,23-double bond starts with the readily available 5-ketone, which is reduced with [JT]-sodium borohydride stereospecificaHy to a 5- [JT]-derivative (40). Carbon-14 labeled avermectins can be obtained by a biosynthetic process using sodium (l- C)propionate as labeled precursor (48). 

Sulfonamides (R2NSO2R ) are prepared from an amine and sulfonyl chloride in the presence of pyridine or aqueous base. The sulfonamide is one of the most stable nitrogen protective groups. Arylsulfonamides are stable to alkaline hydrolysis, and to catalytic reduction they are cleaved by Na/NH3, Na/butanol, sodium naphthalenide, or sodium anthracenide, and by refluxing in acid (48% HBr/cat. phenol). Sulfonamides of less basic amines such as pyrroles and indoles are much easier to cleave than are those of the more basic alkyl amines. In fact, sulfonamides of the less basic amines (pyrroles, indoles, and imidazoles) can be cleaved by basic hydrolysis, which is almost impossible for the alkyl amines. Because of the inherent differences between the aromatic — NH group and simple aliphatic amines, the protection of these compounds (pyrroles, indoles, and imidazoles) will be described in a separate section. One appealing proj>erty of sulfonamides is that the derivatives are more crystalline than amides or carbamates. 

In an effort to prepare 1 2-dihydropapaverine, Buck dehydrated with phosphoryl chloride, and subjected the product (V) to catalytic reduction, followed by the action of phosphorus pentachloride in the cold. The final product was assumed to be 1 2-dihydropapaverine but Young and Robinson interpret this synthesis differently, and their formulae (V) and (VI) are given above, the final product being 3 4-dihydropapaverine (VII), which Buck thus prepared for the first time in a crystalline condition, m.p. 97-8° picrate, m.p. 151° perchlorate, m.p. 238° dec.). 

In section V-A it has been pointed out that catalytic reduction of conjugated enones is usually a good method for the preparation of p- or y-labeled ketones. To overcome certain stereochemical problems, however, it is occasionally necessary to use the lithium-ammonia reduction. In this case deuteration takes place at the / -carbon and generally leads to the thermodynamically more stable product (see chapter 1). 

Catalytic reduction of fluormated aliphatic and aromatic nitro compounds to give oximes and amines was described previously, as was the use of dissolving metals to prepare amines [Si] Refmement of these techniques has resulted in optimized yields and, as indicated in equations 69 and 70, in selective reductions [S6, 87]... 

Catalytic reduction of quinazolines unsubstituted in position 4 using palladium-charcoal, palladium on calcium carbonate, Raney nickel, or Adam s platinum has been used for preparing 3,4-dihydro-... 

Further reduction of 3,4-dihydroquinazoline to l,2,3,Jt-tetTahydro-quinazoline is more difficult, but it can be accomplished with sodium amalgam or by catalytic reduction with palladium-charcoal. 1,2,3,4-Tetrahydroquinazolines have also been prepared by condensing o-aminobenzylamines with various aldehydes and with formaldehyde or methylenediamines (see 3b). 

A further simplification of the requirements for activity came from the preparation of two spasmolytic agents that completely lack the aromatic ring. Thus, double alkylation of phenylace-tonitrile (54) with 1,5-dibromopentane leads to the corresponding cyclohexane (55). This intermediate is then saponified and the resulting acid (56) esterified with w,w-diethylethanolamine. Catalytic reduction of the aromatic ring affords dicyclonine (51). ... 

Reaction of estrone methyl ether with methyl Grignard reagent followed by Birch reduction and hydrolysis of the intermediate enol ether affords the prototype orally active androgen in the 19-nor series, normethandrolone (69). ° (Note that here again the addition of the methyl group proceeded stereoselectively by approach from the least hindered side.) The preparation of the ethyl homolog starts by catalytic reduction of mestranol treatment of the intermediate, 70, under the conditions of the Birch reduction and subsequent hydrolysis of the intermediate enol ether yields norethandrolone (71). ... 

A thioamide of isonicotinic acid has also shown tuberculostatic activity in the clinic. The additional substitution on the pyridine ring precludes its preparation from simple starting materials. Reaction of ethyl methyl ketone with ethyl oxalate leads to the ester-diketone, 12 (shown as its enol). Condensation of this with cyanoacetamide gives the substituted pyridone, 13, which contains both the ethyl and carboxyl groups in the desired position. The nitrile group is then excised by means of decarboxylative hydrolysis. Treatment of the pyridone (14) with phosphorus oxychloride converts that compound (after exposure to ethanol to take the acid chloride to the ester) to the chloro-pyridine, 15. The halogen is then removed by catalytic reduction (16). The ester at the 4 position is converted to the desired functionality by successive conversion to the amide (17), dehydration to the nitrile (18), and finally addition of hydrogen sulfide. There is thus obtained ethionamide (19)... 

Aminonitrile formation on 125 with potassium cyanide and piperidine hydrochloride affords the derivative, 135. Hydrolysis as above gives the corresponding amide (136). Debenzylation is accomplished by catalytic reduction. Alkylation of the secondary amine with the side chain (96) used in the preparation of diphenoxylate affords pirintramide (138) This compound, interest-... 

Methylcyclopentane-l,3-dione has been prepared in 15% yield by the catalytic reduction of 2-mcthylcyclopentane-l,3,5-trione over platinum.2 The present method is based on the original procedure 3 of Panouse and Sannie with improvements as effected by Boyce and Whitehurst4 and the submitters.6... 

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