Aluminum complexes azides

Malonate and related activated methylene compounds have also been used as the nucleophile in conjugate addition/Michael reactions. Taylor and co-workers have developed a new methodology that utilizes (salen)aluminum complexes such as 43 as a catalyst to effect the enantioselective conjugate addition to a,p-unsaturated ketones by a variety of nucleophiles.25 For example, nitriles, nitroalkanes, hydrazoic acids, and azides have found utility in this reaction. Additionally, cyanoacetate (42) has been demonstrated to undergo a highly enantioselective conjugate addition to 41. The Krapcho decarboxylation is then necessary to produce cyanoketone 44, an intermediate in the synthesis of enantioenriched 2,4-cw-di substituted piperidine 45. 

The pyrolysis of aluminum-nitrogen organic complexes, such as diethyl aluminum azide [(C2H5)2A1N3], is also used successfully at low deposition temperatures (450-870°C).0 l Another metallo-organic, hexakis(dimethylamido)dialuminum, reacting with ammonia allows deposition at 200-250°C at atmospheric pressure. 1... 

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

In the presence of gallium chloride, aluminum bromide, aluminum chloride, and ferric chloride, benzoyl azide is decomposed according to eq 2. Here complex formation is very fast, and the decomposition of the complex is the ratedetermining step. The halides do not complex with the phenyl isocyanate formed and, as a consequence, they are not consumed in the reaction. As long as benzoyl azide is in excess, the concentration of the complex is equal to the halide concentration and remains constant. The experimentally determined pseudo-zero-order rate constant depends therefore upon the first power of the initial halide concentration. When, however, the reaction is at a stage where the azide is no longer in excess, the rate of the reaction becomes first order with respect to benzoyl azide and zero order with respect to halide. PhCONj + AlBr, -r - PhCONrAlBr, r+-... 

Whereas aryl, acyl, and sulfonyl azides decompose in the presence of aluminum trichloride in benzene solution only with evolution of N , alkyl azides also split oif significant amounts of N,-.1 -18 At 50° alkylbenzenes and azomethines are obtained. In order to explain these results, Kreher and Jager suggested that two intermediate complexes may be formed (Scheme IV). According to Goubeau, Allenstein, and... 

Several authors have studied the reaction products in the Lewis acid catalyzed decomposition of phenyl and alkyl azides.179-185 Hoegerlee and Butler have found that phenyl azide forms a hydrocarbon-soluble complex at —70° with triethylaluminum, diethylchloroaluminum, and ethyldichloro-aluminum. 1 Upon warming to room temperature, this complex slowly decomposes into an intermediate phenylimine-aluminum compound (25) which then rearranges into a variety of amidoalkylaluminum reaction products (RP) (eq 4). 

Halans has studied the aluminum bromide catalyzed decomposition of phenyl azide in toluene solution at 0° in the presence of traces of hydrogen bromide.1 He has found that an equimolecular complex is formed between the catalyst and phenyl azide and that the catalyst is consumed in the reaction. On the basis of kinetic results, Scheme VI has been proposed for the decomposition mechanism. In connection herewith, Halans observed that whereas an equimolecular mixture of phenyl azide and hydrogen bromide does not decompose at 0°, a mixture of phenyl azide, aluminum bromide, and hydrogen bromide in the ratio 1/1/1 decomposes instantaneously at 0°. 

One problem with this method is that the workup must be done carefully as die amine products tend to complex tenaciously with the aluminum salts formed from the LAH upon workup and thus are not recovered easily. There are standard workups which avoid these issues, but these should be followed carefully. Reduction of azides by catalytic reduction, phosphine or phosphite reagents, or Sn(II) chloride are all effective methods. The azides are also available from displacement reactions and give primary amines upon reduction. 

The reaction of aryl azides with alkenes in the presence of aluminum trichloride gave different products depending on the structure and the geometry of the alkene, the reaction proceeds via the intermediacy of an aziridine 8 complexed with the Lewis acid. Thus aziridines 9 were cleanly obtained from cycloheptene and (Z)-cyclooctene, however, from cyclopentene and cyclohexene a mixture of allylic amines 10 and /5-chloro amines 11 was produced86- 87. The use of 4-chlorophenyl azide in the reaction with cyclohexene gave only a tar. 

Hydroxymethyl-1,4-benzodioxin (137) obtained in 80% yield by reduction of ethyl 1,4-benzo-dioxin-2-carboxylate (39) with lithium aluminum hydride in refluxing ether <91TL5525> reacted with zinc azide bis-pyridine complex under Mitsunobu conditions (triphenylphosphine, diisopropyl azodicarboxylate) to yield exclusively compound (138) in 75% yield. Otherwise, (137) was first reacted with zinc iodide under the same conditions until complete transformation of the starting material into the mixture of regioisomers (139) and (140) excess of dry piperidine was then added to the crude reaction medium to yield the alkenic analogue (141) of Piperoxan <89TL1637>. 

Aluminum azide is obtained from reacting AICI3 with NaNs in THF, or from the reaction of A1H3-Et20 with HN3 in ether at low temperature. When trimethylamine adducts of alane are employed, solids thought to be azido complexes are produced (equation 7). Aluminium (and gallium) compounds X2M(N3), where X = Br or I, have been prepared by the reaction of MX3 with the halogen azide 7W3 in benzene. They are polymeric solids which show v(M—N3) modes near 490 cm" (M = Al), or 430 cm" (Ga) in the vibrational spectra. 

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