Lithium aluminum hydride reaction with

Lithium aluminum hydride, reaction with aldehydes, 610 reaction with carboxylic acids. 611-612... 

In most cases the identity of the reactive reducing species is not known with certainty. For example, the species initially formed by the reaction of lithium aluminum hydride (LAH) with alcohols may not be stable with respect to disproportionation. The degree of association of reducing species may be an important unknown factor in a particular case. Processes other than disproportionation or association may also make it difficult to predict the structure of the reagent formed from the reaction of LAH with sterically hindered alcohols (see Sect. II-A-1). 

Elaboration of 2-isoxazolines via their 4-endo-anions has been studied as a method to synthesize y-amino alcohols (78TL3129,3133,81AG(E)601,603). When the 5-methyl-3-phenyl-2-isoxazoline (527) was deprotonated with LDA/HMPA and methylated with methyl iodide, the tra 5-4,5-substituted isoxazoline (528) was formed predominantly (trans-.cis = 12 1). Reduction of this isoxazoline with lithium aluminum hydride proceeded with steric approach control to provide a diastereomeric mixture of y-amino alcohols (529, 530 Scheme 116). The 5-substituent was found to exhibit a greater steric influence on this reaction than the 4-substituent. 

On the basis of what we have already learned about the reactions of lithium aluminum hydride with aldehydes and ketones (Chapter 18) and the mechanisms presented so far in this chapter, we can readily predict the product that results when hydride reacts with a carboxylic acid derivative. Consider, for example, the reaction of ethyl benzoate with lithium aluminum hydride. As with all of the reactions in this chapter, this reaction begins with attack of the nucleophile, hydride ion, at the carbon of the carbonyl group, displacing the pi electrons onto the oxygen (see Figure 19.7). Next, these electrons help displace ethoxide from the tetrahedral intermediate. The product of this step is an aldehyde. But recall from Chapter 18 that aldehydes also react with lithium aluminum hydride. Therefore, the product, after workup with acid, is a primary alcohol. 

Oxymercuration of simple alkyl- and acyl-substituted cyclopropenes generally results in ring opening.Addition of mercury(II) acetate to 3-methyl-3-phenylcyclopropene, however, gave a low yield of a cyclopropane containing organomercury compound (15-20%), which was converted into an isomeric mixture of 1 -methoxy-2-methyl-2-phenylcyclopropanes by reduction with lithium aluminum hydride. Reaction of 5 with mercury trifluoroacetate in methanol and then sodium hydroxide led predominantly to one cylopropane. ... 

DIMETHYL ETHER (115-10-6) CjHjO Highly flammable, peroxidizable gas. Forms ejqjlosive mixture with air [explosion limits in air (vol %) 3.4 to 18.0 flash point -42°F/-41°C autoignition temp 662°F/350°C Fire Rating 4]. May be heat-and shock-sensitive. Able to form unstable peroxides on prolonged exposxure to air. Violent reaction with oxidizers, aluminum hydride lithium aluminum hydride. Incompatible with strong acids, metal salts. On small fires, use dry chemical powder (such as Purple-K-Powder), dry sand, or COj extinguishers. 

By methods analogous to those cited in the section on hippeastrine, homolycorine (LXVII) afforded a diol upon reduction with lithium aluminum hydride. Treatment with p-toluenesulfonyl chloride followed hy iodide ion gave pluviine jS-methiodide (LXVIII) (mp 232°-233°). This salt was not identical with the known pluviine a-methiodide (mp 259°-261°). Structure proof for LXVJII rests on the pyrolysis of its methochloride to pluviine and anhydromethylpseudolycorine. This interconversion relates the asymmetric centers of pluviine to those of homolycorine and lycorenine. Comparable reactions with a- and j3-dihydrohomolycorine (LXIX and LXX, respectively) converted these compounds to the metho salts of a- and )8-dihydropluviine (LXXI and... 

Active hydrogen in organic substances may be determined by reaction with lithium aluminum hydride labeled with tritium ( H). The activity of released tritium is measured using a proportional counter. 

Methoxy participation has also been encountered in reduction reactions with lithium aluminum hydride and with lithium in liquid am-monia and in the addition of Grignard-type reagents to ketones. ... 

Consider the reaction of lithium aluminum hydride with an ester (Figure 15.34). The hydride will attack the carbonyl to give a tetrahedral intermediate, just as with aldehydes and ketones. However, this tetrahedral intermediate does not wait around to be protonated but loses ethoxide to give an aldehyde. We already know how lithium aluminum hydride reacts with aldehydes, and our final product, after work-up, is a primary alcohol. 

Synthesis by high-dilution techniques requires slow admixture of reagents ( 8-24 hrs) or very large volumes of solvents 100 1/mmol). Fast reactions can also be carried out in suitable flow cells (J.L. Dye, 1973). High dilution conditions have been used in the dilactam formation from l,8-diamino-3,6-dioxaoctane and 3,6-dioxaoctanedioyl dichloride in benzene. The amide groups were reduced with lithium aluminum hydride, and a second cyclization with the same dichloride was then carried out. The new bicyclic compound was reduced with diborane. This ligand envelops metal ions completely and is therefore called a cryptand (B. Dietrich, 1969). 

In contrast to alcohols with their nch chemical reactivity ethers (compounds contain mg a C—O—C unit) undergo relatively few chemical reactions As you saw when we discussed Grignard reagents m Chapter 14 and lithium aluminum hydride reduc tions m Chapter 15 this lack of reactivity of ethers makes them valuable as solvents m a number of synthetically important transformations In the present chapter you will learn of the conditions m which an ether linkage acts as a functional group as well as the methods by which ethers are prepared... 

The reaction of esters with Gngnard reagents and with lithium aluminum hydride both useful m the synthesis of alcohols were described earlier They are reviewed m Table 20 4 on page 848... 

Hydroisoquinolines. In addition to the ring-closure reactions previously cited, a variety of reduction methods are available for the synthesis of these important ring systems. Lithium aluminum hydride or sodium in Hquid ammonia convert isoquinoline to 1,2-dihydroisoquinoline (175). Further reduction of this intermediate or reduction of isoquinoline with tin and hydrochloric acid, sodium and alcohol, or catalyticaHy using platinum produces... 

Good yields of phenylarsine [822-65-17, C H As, have been obtained by the reaction of phenylarsenic tetrachloride [29181-03-17, C H AsCl, or phenyldichloroarsine [696-28-6], C3H3ASCI25 with lithium aluminum hydride or lithium borohydride (41). Electrolytic reduction has also been used to convert arsonic acids to primary arsines (42). Another method for preparing primary arsines involves the reaction of arsine with calcium and subsequent addition of an alkyl haUde. Thus methylarsine [593-52-2], CH As, is obtained in 80% yield (43) ... 

Reduction. Coumarin is reduced to o-hydroxycinnamyl alcohol by reaction with lithium aluminum hydride (21). By reaction with diborane coumarin gives o-aUylphenol [1745-81 -9] (22). 

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. 

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