Lithium tris aluminum

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

The introduction of the l/, 2j5-methylene function into cortical hormones is best carried out by starting with the A -3)S-aIcohols (7) which are prepared by lithium aluminum hydride or lithium tri-t-butoxyaluminum hydride reduction of the corresponding A -3-ketones. 

These reagents generally show increased solubility in organic solvents, particularly at low temperatures, and are useful in certain selective reductions.75 Lithium tri-r-butoxyaluminum hydride and sodium Mv-(2-meLhoxyethoxy)aluminum hydride (Red-Al)76 are examples of these types of reagents that have synthetic use. Their reactivity toward carbonyl groups is summarized in Table 5.3. 

Several reagents reduce aldehydes preferentially to ketones in mixtures of both. Very high selectivity was found in reductions using dehydrated aluminum oxide soaked with isopropyl alcohol and especially diisopropylcarbinol [755], or silica gel and tributylstamane [756]. The best selectivity was achieved with lithium trialkoxyalumimm hydrides at —78°. In the system hexanal/ cyclohexanone the ratio of primary to secondary alcohol was 87 13 at 0° and 91.5 8.5 at —78° with lithium tris(/er/-butoxy)aluminum hydride [752], and 93.6 6.4 at 0° and 99.6 0.4 at —78° with lithium tris(3-ethyl-3-pentyl-oxy)aluminum hydride [752],... 

Transformation of ketones to alcohols has been accomplished by many hydrides and complex hydrides by lithium aluminum hydride [55], by magnesium aluminum hydride [89], by lithium tris tert-butoxy)aluminum hydride [575], by dichloroalane prepared from lithium aluminum hydride and aluminum chloride [816], by lithium borohydride [750], by lithium triethylboro-hydride [100], by sodium borohydride [751,817], by sodium trimethoxyborohy-dride [99], by tetrabutylammonium borohydride [771] and cyanoborohydride [757], by chiral diisopinocampheylborane (yields 72-78%, optical purity 13-37%) [575], by dibutyl- and diphenylstannane [114], tributylstanrume [756] and others Procedure 21, p. 209). 

Reduction of unsaturated ketones to saturated alcohols is achieved by catalytic hydrogenation using a nickel catalyst [49], a copper chromite catalyst [50, 887] or by treatment with a nickel-aluminum alloy in sodium hydroxide [555]. If the double bond is conjugated, complete reduction can also be obtained with some hydrides. 2-Cyclopentenone was reduced to cyclopentanol in 83.5% yield with lithium aluminum hydride in tetrahydrofuran [764], with lithium tris tert-butoxy)aluminium hydride (88.8% yield) [764], and with sodium borohydride in ethanol at 78° (yield 100%) [764], Most frequently, however, only the carbonyl is reduced, especially with application of the inverse technique (p. 21). 

Esters are also reduced by sodium aluminum hydride (yields 95-97%) [<9<9] and by lithium trimethoxyaluminum hydride (2 mol per mol of the ester) [94] but not by lithium tris tert-butoxy)aluminum hydride [96], Another complex hydride, sodium bis(2-methoxyethoxy)aluminum hydride, reduces esters in benzene or toluene solutions (1.1 -1.2 mol per ester group) at 80° in 15-90 minutes in 66-98% yields [969], Magnesium aluminum hydride (in the form of its tetrakistetrahydrofuranate) reduced methyl benzoate to benzyl alcohol in 58% yield on refluxing for 2 hours in tetrahydrofuran [59]. 

A one-liter flask fltted with a stirrer, reflux condenser and separatory flask is charged with 7.6 g (0.2 mol) of lithium aluminum hydride and 500 ml of anhydrous ether. A solution of 44.4 g (0.6 mol) of anhydrous terr-butyl alcohol in 250 ml of ether is added slowly from the separatory funnel to the stirred contents of the flask. (The hydrogen evolved is vented to a hood.) During the addition of the last third of the alcohol a white precipitate is formed. The solvent is decanted and the flask is evacuated with heating on the steam bath to remove the residual ether and tert-butyl alcohol. The solid residue - lithium tri-/er/-butoxyaluminohydride - is stored in bottles protected from atmospheric moisture. Solutions 0.2 m in reagent are prepared by dissolving the solid in diglyme. 

Acylthiazolidine-2-thiones (593), easily prepared from carboxylic acids and thiazolidine-2-thione, can be reduced to the corresponding aldehydes with diisobutyl-aluminum hydride in toluene at -78 to -40 °C in 70-90% yield or with lithium tri-f-butoxyaluminum hydride in THF at -20 to 0 °C in 80-90% yield (Scheme 130) (79BCJ555). The formation of the aluminum-containing six-membered chelate (594) in this reaction process is probable and is supported by the fact that no decrease in yield is observed on changing the mole ratio of DIBAL from 1.2 to 2.1 equivalents. 

Reduction ofpyrimidine-2(lH)-ones.1 The pyrimidinone 2 is reduced by metal hydrides such as lithium tri-f-butoxy aluminum hydride to a mixture of the 3,6- and 3,4-dihydro derivatives in the ratio 9 1. In contrast, Meerwein-Ponndorf-Verley reduction with 1 in isopropanol results only in the 3,4-dihydro derivative (3a) but the reaction is slow and stops after two days to provide only a 25% yield. However, introduction of a halo substituent at C5 results in enhanced yields of the 3,4-dihydro derivatives, with the highest yields obtained with the 5-chloro derivative. 

Triethylaluminum, 204 Triisobutylaluminum, 205 Trimethylaluminum, 22, 205 Vilsmeier reagent-Lithium tri-r-butoxy-aluminum hydride, 342 Boron Compounds Alkyldimesitylboranes, 8 Allenylboronic acid, 36 9-Borabicyclo[3.3.1]nonane, 92 Borane-Dimethylamine, 42 Borane-Dimethyl sulfide-Sodium borohydride, 25... 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

Lithium tris(3-ethyI-3-pentyloxy)aluminum hydride, Li[(C2H5)3CO]3AlH (1). The hydride is prepared in quantitative yield by reaction of 3-ethyl-3-pentanol with LiAlH4. 

Reduction by mild reducing agents converts acyl chlorides, esters, and nitrites into aldehydes. The reducing agents of choice are usually lithium tri-tert-butoxy aluminum hydride (LATB—H) and diisobuty-laluminum hydride (DIBAL—H). Following are the structures for these compounds ... 

Reduction to Aldehydes Reduction of carboxylic acids to aldehydes is difficult because aldehydes are more reactive than carboxylic acids toward most reducing agents. Almost any reagent that reduces acids to aldehydes also reduces aldehydes to primary alcohols. In Section 18-10, we saw that lithium tri-ferf-butoxyaluminum hydride, LiAlH(0-f-Bu)3 is a weaker reducing agent than lithium aluminum hydride. It reduces acid chlorides to aldehydes because acid chlorides are strongly activated toward nucleophilic addition of a hydride ion. Under these conditions, the aldehyde reduces more slowly and can be isolated. Therefore, reduction of an acid to an aldehyde is a two-step process Convert the acid to the acid chloride, then reduce using lithium tri-ferf-butoxyaluminum hydride. 

The sodium borohydride reduction of l-[j8-(3-indolyl)ethyl]-3-hydroxymethylpyridinium bromide (100, R = H) affords a 73% yield-of the 3-piperideine (101), but with the use of lithium aluminum hydride a 50% yield of the diene (102) is obtained. The lithium tri-f-butoxy aluminum hydride reduction of (100) leads to a mixture... 

The product from Step 3 (1.0 eq) was dissolved in THF to give a 0.23 M solution, cooled to 0°C, lithium tri(t-butoxide) aluminum hydride (1 eq) in THF added by canula, and the mixture stirred 3 hours. Thereafter, acetic anhydride (10 eq) was added and the mixture stirred 2 days. The reaction was quenched using a saturated solution of NaHC03 and the product isolated as an oily liquid in 70% purity. 

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