Lithium alanate

To a solution of 0.24 mol of lithium alanate in 500 ml of diethyl ether was added 0.20 mol of the acetylenic alcohol (note 1) at a rate such that gentle refluxing of the diethyl ether was maintained. After the addition the mixture was warmed under reflux for an additional 1 h. It was then cooled to 0 C and subsequently poured on to 400 g of finely crushed ice. After the remaining ice had melted the layers were separated (note 2). The aqueous layer was extracted several times with diethyl ether. The combined ethereal solutions were dried over magnesium sulfate and subsequently concentrated in a water-pump vacuum. Distillation of the residue through... 

For the formation of oxepincarbaldehydes by oxidation of the corresponding alcohols, see Section A.3.1.1.1. and Houben-Weyl, Vol. 4/1 b, p 519 Vol.6/4, p468. For an experimental procedure for the reduction of oxepincarboxylates with lithium alanate to give the corresponding alcohols, see Houben-Weyl, Vol.6/4, p468f. 

When the hydride ion of lithium alanate is used as nucleophile, cyclohexa-2,4-dien-l-ol is obtained as a labile addition product which eliminates water on standing to give benzene.12 The reaction of an oxepin derivative that possesses a hexamethylene bridge across C3-C6 with sodium methoxide gives an addition product 5 in which the seven-membered heterocyclic system is retained.213 214... 

The most stable of the germanium hydrides, R GcI I4 (n = 0,1,2,3), are the tri-organogermanium hydrides, which are prepared by the reduction of the corresponding halides with lithium alanate, or with amalgamated zinc and hydrochloric acid5-7. 

A convenient route to andiides, where Li and A1 centers are, at the same time, involved is represented by the reaction of LiAlH4 with primary silylphosphanes and silylarsanes (Scheme 4) (67). However, the outcome of such reactions is dependent on the stoichiometry. The silylarsane 2c reacts with LiAlH4 in the molar ratio of 4 1 in 1,2-dimethoxyethane, under evolution of H2, resulting in the corresponding tetrakis(arsaneyl)-substituted lithium alanate 36c in quantitative yield. The similar transformation of the arsane 2a with LiAlH4 in the... 

The exhaustive reduction of lactams was preferentially managed by lithium alanate, for instance, with 20 to get 2 (59CCC2318), with 8 and 9a to get 9b and 9c, respectively (65TL1761), with single epimers 167 to get epimers 169, and with 170 to get 171 (7111363). 

Generally, during the first step, a diethyl ether adduct of the alane is synthesized, which should not be isolated and can be used for the next step (Eq. 2) in situ . This method to generate the alane has the advantage with respect to other procedures to start from the easily available lithium alanate (which should be purified before use). The reaction with the alcohol or silanol can be followed by the evolution of gaseous hydrogen. Depending on the acidity of the alcohol or the silanol the reaction mixture has to be cooled. 

Reduction of Diyne Alcohols with Lithium Alanate... 

Reagents i, perbenzoic acid ii, aq. Me2NH iii, 30% H202 iv, thermal fission v, HCl-MeOH vi, lithium alanate vii, MeS02Cl viii, KOH in glycol monomethyl ether... 

Primary and secondary alkyl bromides, iodides, and sulfonates can be reduced to the corresponding alkanes with LiBHEt3 (superhydride) or with lithium aluminum hydride (LiAlH4, other names lithium tetrahydridoaluminate or lithium alanate). If such a reaction occurs at a stereocenter, the reaction proceeds with substantial or often even complete stereoselectivity via backside attack by the hydride transfer reagent. The reduction of alkyl chlorides to alkanes is much easier with superhydride than with LiAlH4. The same is true for sterically hindered halides and sulfonates ... 

Note Owing to the reduction step with lithium alanate, this protocol results in the synthesis of saturated NHC ligands that might be too labile in further catalysis reactions. 

The typical formation route for alane is through the chemical reaction of lithium alanate with aluminum chloride in diethyl ether ... 

SYNS ALUMINUM LITHIUM HYDRIDE LITHIUM ALANATE LITHIUM ALUMINOHYDRIDE UTHIUM ALUMINUM HYDRIDE pOT) UTHIUM ALUMINUM HYDRIDE, ETHEREAL pOT) LITHIUM ALUMNUM TETRAHYDRIDE... 

Aben and Scheeren discovered that bornyloxyaluminum dichloride, which can be easily prepared from bomeol, aluminum chloride, and lithium alanate, acts as an effective catalyst for the hetero Diels-Alder reaction of siloxy dienes and a variety of aldehydes, as illustrated in Sch. 18 [37]. 

Studied for their characteristics of high hydrogen content and low release temperatures [124—126]. Reversibility and kinetic of the hydrogen absorption/ desorption cycle are critical issues also for this class of compounds. NaAlH4 hydride can provide 5.5 wt% of hydrogen under reasonable conditions, by a decomposition reaction made reversible thank to the usage of a catalyst [127], while lithium alanate utilization appears not possible because of the irreversibility of the first decomposition step. 

Corbo P, Migliardini F, Veneri O (2009) Hydrogen release properties of lithium alanate for application to fuel cell propulsion systems. J Power Sources 193 285-291... 

Propargylic lithium alanates or lithium borates react with allylic halides or with carbonyl compounds in a regioselective manner to furnish 1,1 -disubstituted allenes (Scheme 3). ... 

Chen et al. also reported XRD evidence for partial rehydrogenation of the resulting mixture of LiH/Al to an uncharacterized intermediate phase . However, attempts to reproduce this result were unsuccessful. Recently, Ritter and co-workers confirmed the findings of the earlier studies of Ti-doped lithium alanate. These investigators also reported that the kinetics of the formation of the THF adduct of LiAlH4 from the ball milling of THF solutions of dehydrogenated material were improved by the addition of 0.5 mol% of a titanium catalyst. 

Another promising multicomponent system is lithium alanate-lithium amide, this was originally investigated not as a destabilised multicomponent system, but as a means of utilising the lithium amide to destabilise the lithium hydride formed from the decomposition of lithium alanate (i.e. following the reactions for the Li-N-H system as reported by Chen et al. (2002)) and hence release all the hydrogen contained within the alanate (Lu and Fang, 2005) ... 

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