Reductions sodium hydride

Sodium hydride reduction of quinoline in HMPA leads to a 2 3 mixture of 1,2-dihydroquinoline (82) and 1,4-dihydroquinoline (83) isolated as the A-methoxycarbonyl derivatives. In situ produced copper hydride reagents react with pyridinium species with high regioselectivity generating 1,4-dihydropyridine... 

In addition, this synthetic scheme offers a mild reaction route for the degradation of a-hydroxy acids to the corresponding aldehydes containing one less carbon atom or for their conversion to aldehydes with the same number of carbon atoms. For example, reaction of 1,4-diphenylthio-semicarbazide with a-acetoxyacyl chlorides yields 5-(a-hydroxyalkyl)-1,2,4-triazolium salts, which, upon sodium hydride reduction and acid treatment, give benzaldehyde along with 138 (R = H) (Scheme 58) (75TL1889). Moreover, the 5-(a-hydroxyalkyl)-l,2,4-triazolium salts can be easily converted to the 5-alkyl compounds (Scheme 58) and borohydride reduction of the latter followed by acid hydrolysis provides a method for the transformation of a-hydroxy acids to aldehydes with the... 

The route used in the conversion 100 ent-98 is shown in Scheme 10 and begins with the conversion of the former compound into the acetal 101 under standard conditions. Dihydroxylation of the non-chlorinated double-bond within the latter compound using the Upjohn conditions [50] provided the diol 102 (66%) in a completely diastereoselective fashion and this was protected as the corresponding di-MOM ether 103 (88%) using MOM chloride in the presence of sodium hydride. Reductive cleavage of the acetal unit within compound 103 was readily effected in a regioselective manner with DIBAl-H and the ensuing alcohol... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

The mechanism of lithium aluminum hydride reduction of aldehydes and ketones IS analogous to that of sodium borohydride except that the reduction and hydrolysis... 

The carbonyl group of carbohydrates can be reduced to an alcohol function Typi cal procedures include catalytic hydrogenation and sodium borohydnde reduction Lithium aluminum hydride is not suitable because it is not compatible with the solvents (water alcohols) that are required to dissolve carbohydrates The products of carbohydrate reduc tion are called alditols Because these alditols lack a carbonyl group they are of course incapable of forming cyclic hemiacetals and exist exclusively m noncyclic forms... 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

The p-cyanobenzyl ether, prepared from an alcohol and the benzyl bromide in the presence of sodium, hydride (74% yield), can be cleaved by electrolytic reduction (—2.1 V, 71% yield). It is stable to electrolytic removal ( — 1.4 V) of a tritylone ether [i.e., 9-(9-phenyl-10-oxo)anthiyl ether]. ... 

Methylindole has also been prepared by lithium aluminum hydride reduction of 1-methylindoxyl. Compounds giving rise to NH absorption in the infrared (indole, skatole) can be completely removed by refluxing the crude 1-methylindole over sodium for 2 days and then distilling the unreacted 1-methylindole from the sodio derivatives and tarry decomposition products. 

Mescaline, a hallucinogenic amine obtained from the peyote cactus, has been synthesized in two steps from 3,4,5-trimethoxybenzyl bromide. The first step is nucleophilic substitution by sodium cyanide. The second step is a lithium aluminum hydride reduction. What is the structure of mescaline ... 

Lithium aluminum hydride reduction of pyridinium salts is very similar to sodium horohydride reduction and gives similar products, but the ratio of 1,2- and 1,4-dihydro- or tetrahydropyridines differs considerably (5). Isoquinolinium salts are reduced hy sodium borohydride or lithium aluminum hydride in a manner identical to pyridinium salts (5). Quino-linium salts are reduced by sodium borohydride to give primarily tetra-hydroquinolines (72) as shown by the conversion of 33 to 34 and 35. When lithium aluminum hydride is used, the product is usually the dihydroquinoline (73) as shown in the conversion of 36 to 37 and 38. 

Thus the critical synthetic 1,6-dihydropyridine precursor for the unique isoquinuclidine system of the iboga alkaloids, was generated by reduction of a pyridinium salt with sodium borohydride in base (137-140). Lithium aluminum hydride reduction of phenylisoquinolinium and indole-3-ethylisoquinolinium salts gave enamines, which could be cyclized to the skeletons found in norcoralydine (141) and the yohimbane-type alkaloids (142,143). 

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