Lithium aluminum hydride reductions

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

Which of the isomeric C5H12O alcohols can be prepared by lithium aluminum hydride reduction of... 

Epoxidation of an alkene followed by lithium aluminum hydride reduction of the result mg epoxide gives the same alcohol that would be obtained by acid catalyzed hydration (Section 610) of the alkene... 

Lithium aluminum hydride reduction (Sec tion 15 3) Carboxylic acids are reduced to primary alcohols by the powerful reducing agent lithium aluminum hydride... 

Amines of the formula n 2n+ be prepared by the lithium aluminum hydride reduction of the corresponding amide, hydrogenolysis... 

The versatility of lithium aluminum hydride permits synthesis of alkyl, alkenyl, and arylsilanes. Silanes containing functional groups, such as chloro, amino, and alkoxyl in the organic substituents, can also be prepared. Mixed compounds containing both SiCl and SiH cannot be prepared from organopolyhalosilanes using lithium aluminum hydride. Reduction is invariably complete. 

An 80% yield of tetraphenylfuran is obtained by treatment of benzoyl chloride with active titanium generated by lithium aluminum hydride reduction of titanium trichloride (Scheme 84e) (8UOC2407). The reaction nroceeds via benzil and tetraphenylbut-2-ene-l,4-dione, both of which are minor products of the reaction. 

Besides the salts (458) and (459) previously described, aminopyrazolium salts can be obtained from the reaction between amines and chloropyrazolium salts (Section 4.04.2.3.7(ii)) or by quaternization of iminopyrazplines as in (461)—> (462) (72BSF2807). The lithium aluminum hydride reduction of the salt (462) affords mixtures of reduced and open-chain pyrazoles (Figure 23 Section 4.04.2.1.6(i)). 

Lithium aluminum hydride reduction of 2,3,4-triphenylisoxazolin-5-one yielded 1,2,3-triphenylaziridine and dibenzylaniline. The reaction was considered to proceed by a concerted [l,3]-sigmatropic migration of the N to a C atom. HOMO-LUMO calculations show this type of concerted reaction is possible (Scheme 68) (80JA1372). 

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. 

Neopentyl alcohol has been made by lithium aluminum hydride reduction of trimethylacetic acid and by treating ferf-butyl-magnesium chloride with methyl formate. ... 

Kyba and eoworkers prepared the similar, but not identical compound, 26, using quite a different approach. In this synthesis, pentaphenylcyclopentaphosphine (22) is converted into benzotriphosphole (23) by reduction with potassium metal in THF, followed by treatment with o "t/20-dichlorobenzene. Lithium aluminum hydride reduction of 23 affords l,2-i>/s(phenylphosphino)benzene, 24. The secondary phosphine may be deprotonated with n-butyllithium and alkylated with 3-chlorobromopropane. The twoarmed bis-phosphine (25) which results may be treated with the dianion of 24 at high dilution to yield macrocycle 26. The overall yield of 26 is about 4%. The synthetic approach is illustrated in Eq. (6.16), below. 

Some instances of incomplete debromination of 5,6-dibromo compounds may be due to the presence of 5j5,6a-isomer of wrong stereochemistry for anti-coplanar elimination. The higher temperature afforded by replacing acetone with refluxing cyclohexanone has proved advantageous in some cases. There is evidence that both the zinc and lithium aluminum hydride reductions of vicinal dihalides also proceed faster with diaxial isomers (ref. 266, cf. ref. 215, p. 136, ref. 265). The chromous reduction of vicinal dihalides appears to involve free radical intermediates produced by one electron transfer, and is not stereospecific but favors tra 5-elimination in the case of vic-di-bromides. Chromous ion complexed with ethylene diamine is more reactive than the uncomplexed ion in reduction of -substituted halides and epoxides to olefins. ... 

An alternate method of producing the 21-hydroxy-20-ketone consists in lithium aluminum hydride reduction of the dimethyl acetal, hydrolysis to the 20-hydroxy-21-aldehyde and rearrangement, preferably via the bisulfite addition product... 

In contrast to alcohols with their- rich chemical reactivity, ethers (compounds containing a C—O—C unit) undergo relatively few chemical reactions. As you saw when we discussed Grignaid reagents in Chapter 14 and lithium aluminum hydride reductions in Chapter 15, this lack of reactivity of ethers makes them valuable as solvents in a number of synthetically important transfonnations. In the present chapter you will leain of the conditions in which an ether linkage acts as a functional group, as well as the methods by which ethers are prepared. 

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 ... 

The preparation of enamines by reduction of aromatic heterocyclic bases and their quaternary salts or of lactams is not the most useful approach (97). The lithium aluminum hydride reduction of N-acyl enamines has been used with both fruitful and unsuccessful results. A series of 3-N-acetyl -d -cholestenes (104) has been prepared by desulfurization of the appropriate thiazolidine (105) (98,99). Lithium aluminum hydride reduction of the... 

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. 

On treatment of N-methylpapaverine, formed by the lithium aluminum hydride reduction of papaverine methiodide with phosphoric acid, N-methylpavine is formed which is identical with the racemic alkaloid argemonine. This reaction was used for the synthesis of the alkaloid (-h)-coreximine (268) (174) and similar compounds containing the proto-berberine grouping in the molecule (269,270). 

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). 

The chemical reduction of enamines by hydride again depends upon the prior generation of an imonium salt (111,225). Thus an equivalent of acid, such as perchloric acid, must be added to the enamine in reductions with lithium aluminum hydride. Studies of the steric course (537) of lithium aluminum hydride reductions of imonium salts indicate less stereoselectivity in comparison with the analogous carbonyl compounds, where an equatorial alcohol usually predominates in the reduction products of six-membered ring ketones. 

Catalytic hydrogenation of 57 affords 2-phenylacetamidopropionic acid (66) or its ester by solvolytic opening of the initially formed 5(4 )-oxazolone. Lithium aluminum hydride reduction gives the... 

Unequivocal syntheses of cis- and mns-(i -decahydroquinoxalincs have been achieved by lithium aluminum hydride reduction of the corresponding cis- and trans-decahydroquinoxaIin-2-ones. The latter compounds were prepared by condensation of chloroacetic acid and cis- and trans-1,2-diaminocyclohexane, respectively. The resolution of frans-dUdecahydroquinoxaline was effected by use of first dibenzoyl-cZ-tartaric acid and then of dibenzoyl- -tartaric acid. "" (C/. p. 215.)... 

The correct structure (3) for this compound was first proposed in 1922 by Pieroni and Moggi on the basis of the isolation of succinic acid by chromic acid oxidation. Full confirmation of this structure was more recently obtained by Potts and Smithby the degradation outlined in Scheme 1. The dipyrrylbutane was synthesized by the lithium aluminum hydride reduction of the known dipyrrylbutane-... 

An alternative route to a furanosyl halide of 2-deoxy-D-nbo-hexose was envisaged, involving the lithium aluminum hydride reduction of ethyl 2,3-anhydro-/ -D-allofuranoside which could, presumably, lead to ethyl... 

Butylcyclohexanol has been prepared from />-/-butylphenol by reduction under a variety of conditions.3 4 Winstein and Holness5 prepared the pure trans alcohol from the commercial alcohol by repeated crystallization of the acid phthalate followed by saponification of the pure trans ester. Eliel and Ro 6 obtained 4-f-butylcyclohexanol containing 91% of the trans isomer by lithium aluminum hydride reduction of the ketone. Iliickel and Kurz 7 reduced />-/-butylphenol with platinum oxide in acetic acid and then separated the isomers by column chromatography. 

Woodward s strychnine synthesis commences with a Fischer indole synthesis using phenylhydrazine (24) and acetoveratrone (25) as starting materials (see Scheme 2). In the presence of polyphosphor-ic acid, intermediates 24 and 25 combine to afford 2-veratrylindole (23) through the reaction processes illustrated in Scheme 2. With its a position suitably masked, 2-veratrylindole (23) reacts smoothly at the ft position with the Schiff base derived from the action of dimethylamine on formaldehyde to give intermediate 22 in 92% yield. TV-Methylation of the dimethylamino substituent in 22 with methyl iodide, followed by exposure of the resultant quaternary ammonium iodide to sodium cyanide in DMF, provides nitrile 26 in an overall yield of 97%. Condensation of 2-veratryl-tryptamine (20), the product of a lithium aluminum hydride reduction of nitrile 26, with ethyl glyoxylate (21) furnishes Schiff base 19 in a yield of 92%. 

From intermediate 28, the construction of aldehyde 8 only requires a few straightforward steps. Thus, alkylation of the newly introduced C-3 secondary hydroxyl with methyl iodide, followed by hydrogenolysis of the C-5 benzyl ether, furnishes primary alcohol ( )-29. With a free primary hydroxyl group, compound ( )-29 provides a convenient opportunity for optical resolution at this stage. Indeed, separation of the equimolar mixture of diastereo-meric urethanes (carbamates) resulting from the action of (S)-(-)-a-methylbenzylisocyanate on ( )-29, followed by lithium aluminum hydride reduction of the separated urethanes, provides both enantiomers of 29 in optically active form. Oxidation of the levorotatory alcohol (-)-29 with PCC furnishes enantiomerically pure aldehyde 8 (88 % yield). 

The homology between 22 and 21 is obviously very close. After lithium aluminum hydride reduction of the ethoxycarbonyl function in 22, oxidation of the resultant primary alcohol with PCC furnishes aldehyde 34. Subjection of 34 to sequential carbonyl addition, oxidation, and deprotection reactions then provides ketone 21 (31% overall yield from (—)-33). By virtue of its symmetry, the dextrorotatory monobenzyl ether, (/ )-(+)-33, can also be converted to compound 21, with the same absolute configuration as that derived from (S)-(-)-33, by using a synthetic route that differs only slightly from the one already described. 

Sequential esterification, lithium aluminum hydride reduction, and acetylation converted 84 into compound 86. cw-Hydroxylation of 86 with... 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

Thermal decarboxylation of 119 provided the cyclohexene derivative 120, which gave compound 121 by lithium aluminum hydride reduction. Hydroboration - oxidation of 121, followed by acetylation, gave carba-sugar derivatives (122 and 123) in equal yields. 

The products are liberated by hydrolysis of the aluminum alkoxide at the end of the reaction. Lithium aluminum hydride reduction of esters to alcohols involves an elimination step in addition to hydride transfers. 

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