Aluminum alkoxides synthesis

Ooi, T., Miura, T., Itagaki, Y., Ichikawa, H., Maruoka, K. Catalytic Meerwein-Ponndorf-Verley (MPV) and Oppenauer (OPP) reactions remarkable acceleration of the hydride transfer by powerful bidentate aluminum alkoxides. Synthesis 2002, 279-291. 

To sum up, the living character of the aluminum alkoxide mediated ROP of lactones has permitted the synthesis of novel ABA triblock copolymers, the composition and molecular weight of which can purposely be tuned up for displaying excellent elastomeric properties. Interestingly, the inherent biodegradability of each partner, PCL and PDXO, would open up new applications for these novel thermoplastic elastomers. 

X= CHjBr, (CH2)2-CH=CH2, CH CHjNEtj Fig. 10 Synthesis of functionalized aluminum alkoxides... 

As indicated in Scheme 27, indoles may be alkylated by their acid-catalyzed reaction with alcohols. Similarly, r-butylation of pyrroles has been effected by the acid-catalyzed reaction with t- butyl acetate (B-77MI30502), and the diarylmethylation of 1-methylpyrrole from the acid-catalyzed reaction with the chromium trichloride complex of the diarylcarbinol has been described (78JA4124). The alkylation of indoles by alcohols in the presence of the aluminum alkoxide and Raney nickel appears to be efficient for the synthesis of 3-substituted indoles, but is less successful in the alkylation of 2-methylindole (79JHC501). The corresponding isopropylation of pyrrole produces 2,5-diisopropylpyrrole and 1-isopropylpyrrolidine, as the major products (79JHC501). 

Production of alumina aquosols from alumina has been well researched in sol-gel science [19]. Yoldas [20] was the first one to show that monolithic alumina gels could be formed by hydrolysis and condensation of aluminum alkoxide. As discussed in Chapter 5, formation of aquosols and their gel is an intermediate step in the formation of chemically bonded phosphate ceramics. Condensation of the hydrated alumina sols by reaction with phosphoric acid to form A1(H2P04)3-H20 gel is the first step toward synthesis of a berlinite-bonded alumina ceramic. When this gel is heated to 150°C, this gel reacts with additional alumina and releases water, and crystalline berlinite is produced. This Chapter... 

Thirty-three grams (0.19 mol) of aluminum ethoxide is vacuum-distilled into a 250-ml. round-bottomed flask, and 80 g. (0.6 mol) of vacuum-distilled ethyl acetoacetate (59.8° at 8 mm.) is added. Other aluminum alkoxides cannot be substituted successfully for aluminum ethoxide in this synthesis since some substitution of the alkyl group of the alk-oxide, for ethyl, appears to occur in the resulting aluminum acetoacetate derivative. The flask is fitted with a reflux condenser, and the mixture is heated gently with an oil bath the temperature is raised gradually from 85 to 140° over a period of 4 hours. The aluminum ethoxide dissolves slowly as the reaction proceeds, and the ethyl alcohol formed is distilled off at 170° and 25 mm. (A considerably lower temperature can be used if a better vacuum source is available.) At the end of 4 hours the product is cooled to room... 

Relatively few studies on the synthesis of mesoporous alumina have been reported to date [8]. One of the limitations of the reported synthetic strategies is that the rate of hydrolysis (and condensation) reaction of aluminum alkoxide are much faster than that of silicon alkoxide. In this study, we proposed a novel method to prepare bimodal porous aluminas with meso- and macropores with narrow pore size distribution and well-defined pore channels. The fiamewoik of the porous alumina is prepared via a chemical templating method using alkyl caiboxylates. Here, self-assemblied micelles of carboxylic acid were used as a chemical template. Mesoporous aluminas were prepared through carefiil control of the reactants pH, while the procedures are reported elsewhere [9]. 

The earliest report of a reaction mediated by a chiral three coordinate aluminum species describes an asymmetric Meerwein-Poimdorf-Verley reduction of ketones with chiral aluminum alkoxides which resulted in low induction in the alcohol products [1]. Subsequent developments in the area were sparse until over a decade later when chiral aluminum Lewis acids began to be explored in polymerization reactions, with the first report describing the polymerization of benzofuran with catalysts prepared from and ethylaluminum dichloride and a variety of chiral compounds including /5-phenylalanine [2]. Curiously, these reports did not precipitate further studies at the time because the next development in the field did not occur until nearly two decades later when Hashimoto, Komeshima and Koga reported that a catalyst derived from ethylaluminum dichloride and menthol catalyzed the asymmetric Diels-Alder reaction shown in Sch. 1 [3,4]. This is especially curious because the discovery that a Diels-Alder reaction could be accelerated by aluminum chloride was known at the time the polymerization work appeared [5], Perhaps it was because of this long delay, that the report of this asymmetric catalytic Diels-Alder reaction was to become the inspiration for the dramatic increase in activity in this field that we have witnessed in the twenty years since its appearance. It is the intent of this review to present the development of the field of asymmetric catalytic synthesis with chiral aluminum Lewis acids that includes those reports that have appeared in the literature up to the end of 1998. This review will not cover polymerization reactions or supported reactions. The latter will appear in a separate chapter in this handbook. 

The mesoporous aluminas synthesized using a nonionic templating method are thermally stable not only to template removal, but also to prolonged heating at elevated temperature. Therefore, these aluminas would be able to maintain their unique structural features in fairly demanding catalyst preparations and catalytic applications. Unlike sol-gel-derived aluminas, the synthesis temperature used for the hydrolysis and condensation of the aluminum alkoxide did not affect the resulting thermal evolution from the aluminum hydroxide to transitional alumina and the subsequent thermal stability of the transitional alumina. The only observed effect of synthesis temperature was the impact on median pore diameter and pore volume.[231]... 

Irrespective of the solvent the aldehyde, acid or ester 1 is first transformed into the aluminum alkoxide 5. Transfer of hydride to the C-C double bond to give 6 occurs only when electron density is delivered to aluminum by a solvent with Lewis base character. Only in solvents of strong Lewis basicity (tetrahydrofuran, 1,2-dimethoxyethane) is the carbanionic character of the C-Al bond (e.g. 7) sufficient to induce intramolecular substitution to give phenylcyclo-propane 4. " 3-Phenylpropanols 3 are byproducts in the synthesis of 4, if insufficient reflux time is applied before acidic workup. ... 

Synthesis of organized mesoporous aluminas is based on the same approaches as those successfully used for the synthesis of mesoporous molecular sieves ( anionic , cationic , and neutral ) using aluminum alkoxide as the source of aluminum and in the absence of any silicon source. In contrast to the synthesis of siliceous MCM-41, the cationic route to organized mesoporous aluminas using hexadecyltrimethylammonium cations is the least applied and understood. Cabrera et al. [68] described the possibility to tailor the pore dimensions from 3.3 to 6.0 nm by modifying the ratio of surfactant, water and triethanolamine however, this synthesis route seems to be less reproducible compared with anionic and neutral routes. 

Other methods have also been used for the synthesis of macromonomers. For example the synthesis of poly(D,L)-lactide macromonomers was reported [225]. It is known that aluminum alkoxides can be used as initiators for the polymerization of lactides via a coordination-insertion mechanism. A functional initiator was prepared by the reaction of triethylaluminum with 2-hydroxyethyl-methacrylate (HEMA) as shown in the following Scheme 71. 

Successful MPV reduction of aliphatic P-aminoaldehydes to their corresponding y9-aminoalcohols was reported by Hayes and Drake (31). However, since the introduction of LiAIH4 in 1947 and the growth in usage of complex metal hydride reducing agents, aluminum alkoxides have fallen out of favor in organic synthesis. 

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