LiAIH, reduction

Hydride reduction of 4-fert-butylcyclohexanone 3 shows a preference for axial addition [axial additioniequatorial addition = 91-88.5 9-11.5 (LiAIH ) [16,17, 50, 51] or 87-86 13-14 (NaBH )] [50, 52]. Addition of acetyhde anion, Na(Li or K) C=CH, also showed a similar axial preference [14, 15, 53]. 

Diborane was used in this reduction, but LIAIH -should do just as well. 

Reduction of amino acids to amino alcohols.3 Amino acids can be reduced directly to the corresponding amino alcohols by LiAIH, in refluxing THF in 70-... 

This is a reduction reaction and the LIAIH is such a strong reducing agent that it reduces the carboxylic acid directly to the primary alcohol. 

Nitriles on reduction with lithium aluminium hydride (LIAIH ) or catalytic hydrogenation produce primary amines. This reaction is used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine. 

By reduction of the initial condensation product with sodium borohydride. reduction of the initial condensation product with LiAIH at -78 0. 

LiAIH(OEt)3,345 DIBALH,346 and NaAIH4.347 The metal hydride method is useful for aliphatic and aromatic nitriles. Reduction to the aldehyde has also been accomplished by treatment of the nitrile with sodium hypophosphate and Raney nickel in aqueous acetic acid-pyridine or formic acid,348 and with zinc and a Cob(I)alamin catalyst in aqueous acetic... 

Formation of an Alcohol The simplest reaction of a tetrahedral alkoxide intermediate is protonation to yield an alcohol. We ve already seen two examples of thi.s kind of process during reduction cif ketones and uldchydcs with hydride reagents such as NaBH, and LiAIH (Section 17.5), and during Qrignard reactions (Section 17.6). In the case of reduction, the nucleophile that adds to the carbonyl group is a hydride ion, H while in the case of Grignard reaction, the nucleophile is a carbanion, R ,C . ... 

Selective reduction of functional groups can be achieved by chemical modification of the LiALH4 for example, lithium tri(t-butoxy)aluminium hydride [LiAIH(t-OBu)3] is a more selective reagent, and reduces aldehydes and ketones, but slowly reduces esters and epoxides. Nitriles and nitro groups are not reduced by this reagent. Carboxylic acids can be converted into the aldehyde via acid chloride with lithium tri(tert-butoxy) aluminium hydride at a low temperature (—78°C). The nitro compounds are not reduced under this condition. Thus, selective reduction of 3,5-dinitrobenzoic acid (6.45) to 3,5-dinitrobenzaldehyde (6.47) can be achieved in two steps. First, 6.45 is converted into 3,5-dinitrobenzoyl chloride (6.46) and then LiAlH(t-OBu)3 reduction of 6.46 gives 6.47. 

Q> I Mechanism 20.5 Reduction of an Amide to an Amine with LiAIH ... 

With LiAiH[OC(CH3)3]3, a milder reducing agent, reduction stops at the aldehyde stage. 

Boireau, G. Deberly, A. Toneva, R. Synlett 1993, 585. In this study, reduction with LiAIH(Ot-Bu)3 was shown to give primarily the trans-alcohol. 

Problem 17.8 What carbonyl compounds give the following alcohols on reduction with LiAIH Show all possibilities. 

Numerous data have been recorded concerning the stereochemistry of the reduction of the substituted cyclohexanone derivatives, and in general, preferential axial attack occurs with LiAIH, derivatives, whereas equatorial attack takes place for trialkylborohydrides. This tendency is valid for this case and it is noteworthy that (IS, 3R)-3-(/ -tert-butylphenylthio)cyclohexanol is obtained almost exclusively by employing LiAlH(OBu )3 (entry 9). Thus, the 3-arylthio asymmetric center is effectively transferred to C-1, producing both configurational isomers (R and S) by suitable choice of reducing reagent. 

It Cp ZrH . This ziicontum reagent ts oh-tamed as a white solid by reduction of (C ZiCI)iO unth LiAIH, in THE in 66% yield. ... 

Experiments showed that reduction of (38) with LiAiH gave substantial amounts of both diols which could be separated by chromatography. Tosylation gave the required (35) and (36), The effort wns worthw hiie as dramatically different reactions occurred on treatment with base to give (39) and (40). 

Section 8-6 presents two u.seful reduction processes. Carbonyl compounds such as ketones and aldehydes arc useful precursors (starting materials) for the synthesis of alcohols. Either metal-catalyzed Ht addition or reaction with the hydride reagents NaBH and LiAIH converts aldehydes to primary alcohols. The same processes convert ketones to secondary alcohols. The.se hydride reductions are the lirst of many examples that you will. see of nucleophilic additions to the electrophilic carbons of carbonyl groups. This is one of the most important clas.ses of reactions in organic chemistry. 

Chromium(III) chloride-Lithium aluminum hydride. The reagent is prepared by reduction of 2 equiv. of anhydrous CrC j with 1 equiv. of LiAIH, in THF at 0 and is presumably chromium(ll) chloride. The advantage of this new chromium... 

Hexafluoroacetone is a reactive electrophile. It reacts with activated aromatic compounds (e.g., phenol), and can be condensed with olefins, dienes, ketenes, and acetylenes. It forms adducts with many compounds containing active hydrogen (e.g., H O or HCN). Reduction of HFA with NaBH or LIAIH affords the useful solvent hexafluorolsopropyl alcohol. The Industrial Importance of HFA arises largely from Its use In polymers and as an... 

Reduction of (160) with LiAlH or LiAIH -AIClj in molar ratio 3 I gave a ca. 50 50 ratio of cis- and trans-alcohols, whereas ca. 70 % cis-alcohol was formed with AIH3 or LiAl(OMe)3H. However, greater selectivity was exhibited in reductions of (157) where proportions of cis-alcohol ranged from ca. 75% with LiAlH to 100% with LiAl(OMe)3H. 

Reduction of the vinylogous urethane (518) with LiAIH led directly to (519), which was readily hydrolysed to tetronic acid (520). ... 

Similarly, reduction of both aromatic and aliphatic aldehydes and ketones where there is a chlorine (Cl) or bromine (Br) present elsewhere in the carbonyl-containing compound succeeds with sodium borohydride (NaBH,) and, occasionally, with lithium aluminum hydride (LiAIH,) at low temperatures. Catalytic reduction frequently leads to hydrogenolysis of the halogen, producing the halogen-free alcohol. 

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