Alane tetrahydrofuran

The spheres which were soaked in the sodium alanate tetrahydrofuran solution were cracked open by applying a slight pressure and the interior of a cracked sphere was investigated and Fig.4 show s the interior of a cracked glass sphere. 

Auch durch Bildung von Koordinationsverbindungen wird nach (5) ge-bildetes Alan stabilisiert. So resultiert beim Behandeln von aktiviertem Al-Pulver mit H2 bei 70°C und 170 atu Druck in Gegenwart von Tri-athylendiamin und Tetrahydrofuran (THF) in 6 Stunden eine 92-proz. Ausbeute an polymerem Triathylendiamin-alan nach (6) (3). 

Tetrahydrofuran itself is not entirely inert to some hydrides although it is a favorite solvent for reductions with these reagents. A mixture of lithium aluminum hydride and aluminum chloride produced butyl alcohol on prolonged refluxing in yields corresponding to the amount of alane generated [633]. 

The reason why the carbonyl group in -santonin remained intact may be that, after the reduction of the less hindered double bond, the ketone was enolized by lithium amide and was thus protected from further reduction. Indeed, treatment of ethyl l-methyl-2-cyclopentanone-l-carboxylate with lithium diisopropylamide in tetrahydrofuran at — 78° enolized the ketone and prevented its reduction with lithium aluminum hydride and with diisobutyl-alane (DIBAL ). Reduction by these two reagents in tetrahydrofuran at — 78° to —40° or —78° to —20°, respectively, afforded keto alcohols from several keto esters in 46-95% yields. Ketones whose enols are unstable failed to give keto alcohols [1092]. 

In dicarboxylic acids with one free and one esterified carboxyl group the free carboxyl only may be reduced with hydrides (alanes, boranes). The monoethyl ester or adipic acid was converted by an equimolar amount of borane in tetrahydrofuran at —18° to 25° to ethyl 6-hydroxyhexanoate in 88% yield [971] Procedure 19, p. 209). 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

Reduction of o /i-unsatin-ated lactams, S,6-dihydro-2-pyridones, with lithium aluminum hydride, lithium alkoxyaluminum hydrides and alane gave the corresponding piperidines. 5-Methyl-5,6-dihydro-2-pyridone (with no substituent on nitrogen) gave on reduction with lithium aluminum hydride in tetrahydrofuran only 9% yield of 2-methylpiperidine, but l,6-dimethyl-5,6-dihydro-2-pyridone and 6-methyl-l-phenyl-5,6-dihydro-2-pyridone afforded 1,2-dimethylpiperidine and 2-methyl-1-phenylpiperidine in respective yields of 47% and 65% with an excess of lithium aluminum hydride, and 91% and 92% with alane generated from lithium aluminum hydride and aluminum chloride in ether. Lithium mono-, di- and triethoxyaluminum hydrides also gave satisfactory yields (45-84%) [7752]. 

Amides containing nitro groups are reduced to diamino compounds with alane. A, A -Dimethyl-p-nitrobenzamide, on reduction with lithium aluminum hydride in the presence of sulfuric acid in tetrahydrofuran, gave 98% yield of dimethyl-p-aminobenzylamine [1117]. 

Even better yields are obtained with alane produced in situ from lithium aluminum hydride and 0.5mol of 100% sulfuric acid in tetrahydrofuran [994], or 1 mol of aluminum chloride in ether [787] Procedure 17, p. 208). One or 1.3 mol of the alane is used per mole of the nitrile and the reduction is carried out at room temperature. Comparative experiments showed somewhat higher yields of amines than those obtained by lithium aluminum hydride alone [787]. 

Treatment of l,4-diazabicyclo[2.2.2]octane in tetrahydrofuran (THF) with activated Al powder at 70 C under 34 MPa of forms the Al—H bond as the amine alane ... 

Similar free radicals with Al—N bonding but without hydrocarbon groups on the aluminum can be obtained either from the 3 1 adduct of 2,2 -di-pyridyl and aluminum chloride by the action of dilithium-dipyridyl in tetrahydrofuran 96), or from lithium alanate and 2,2 -dipyridyl with spontaneous liberation of hydrogen 96). By analogy with the diethylalanylpyridine radical described above, the following structure for the complex Al(dipyridyl)a can be suggested ... 

The most studied adducts are the trialkylamine alanes. Trimethylamine reacts to give both 1 1 and 2 1 adducts with AIH3, but the latter is stable only in the presence of an excess of amine. The monoamine has a tetrahedral structure (4) and is a white, volatile crystalline solid (mp 75 °C) that is readily hydrolyzed by water. Like the etherate, it slowly decomposes to (AlHs). The bisamine has a trigonal bipyramidal stmcture with the amines in the axial positions (5). This was the first compound in which aluminum was demonstrated to adopt a five-coordinate structure. Tetrahydrofuran also gives 1 1 and 1 2 complexes but diethyl ether only gives the 1 1 complex. 

Following the established purifications and isomerization in trifluoroacetic acid and chloroform at room temperature provided the pure tran -tetrahydrofuran (241) in 54% overall yield starting from 274. The trans-isomer (241) on reduction with alane-dimethylethylamine complex afforded the amino methyl compound in 95% yield, which was converted to the reqnisite nrea (229) by using p-nitrophenylchloro-formate. 

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