Carbonyls tris aluminum

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 modifications have been made to organoaluminum-based catalysts. Methylaluminum bis(2,6-di-tert-butyl-4-alkylphenoxide) (MAD) shows high diastereofacial selectivity in carbonyl alkylation (Scheme 72).31 11 Aluminum tris(2,6-diphenylphenoxide) (ATPH) has been developed as a catalyst for conjugate addition reactions. Since a carbonyl group is stabilized by steric effect of ATPH, the 1,4-adduct is obtained selectively.312... 

In the fourth and final chapter, Howard Haubenstock discusses asymmetric reduction of organic molecules. Within this general topic of wide and continuing interest, Haubenstock s chapter deals with chiral derivatives of lithium aluminum hydride, their preparation from suitable amino or hydroxy compounds, and their use in reducing carbonyl groups. Related reactions of the Meerwein-Ponndorf-Verley type or involving tri-alkylaluminum reagents are also presented. 

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). 

Aluminum chloride, 15 Arenediazonium tetrafluoroborates, 19 Rhodium(II) carboxylates, 266 Tris(dimethylamino)sulfonium difluoro-trimethylsilicate, 336 Asymmetric reactions Addition reactions to carbonyl groups Bis(2,4-dimethyl-3-pentyl) tartrate, 36 (S)-( + )-2-Methoxymethylpyrrolidine, 180... 

Tris(dimethylamino)sulfonium difluo-rotrimethylsilicate, 336 Xenon(II) fluoride, 345 Alkyl bromides Potassium permanganate, 258 Sodium bromide, 46 Tetraethylammonium bromide, 46 Alkyl iodides Aluminum iodide, 17 Potassium permanganate, 258 Sodium iodide, 46 Tetraethylammonium iodide, 46 Alkynes (see also Acetylenic carbonyl compounds, Diynes, Enynes, Propar-gyl alcohols)... 

Saito, S. Shiozawa, M. Nagahara, T. Nakadai, M. Yamamoto, H. Molecular recognition of carbonyl compounds using aluminum tris(2,6-diphenylphenoxide) new regio- and stereoselective alkylation of a,/ -unsaturated carbonyl compounds./. Am. Chem. Soc. 2000, 122, 7847-7848. 

This amphiphilic conjugate alkylation system has been improved to a synthetically useful level by the development of aluminum tris(2,6-diphenylphenoxide) (ATPH) as a highly efficient carbonyl stabilizer, thereby achieving a practical conjugate addition procedure. 

The exceedingly bulky aluminum reagent aluminum tris(2,6-di-rert-butyl-4-methyl-phenoxide) (ATD) [140] was found to be superior to ATPH or MAD as a carbonyl protector in the alkylation of ynones [141]. Initial complexation of 3-octyn-2-one (13S) in toluene with ATD and subsequent addition of a hexane solution of BuLi at -78 °C generated 1,4 adduct 136 in 93 % yield together with a small amount of the 1,2 adduct (Sch. 103). 

Acetone, cyclohexanone, benzophenone, cinnamaldehyde, and other carbonyl compounds are hydrogen acceptors in the Oppenauer oxidation of alcohols to carbonyl compounds. The reaction is catalyzed by Raney nickel [961], aluminum alkoxides [962], tris(isopropoxide), or tris(tert-bu-toxide) as bases soluble in organic solvents [963, 964]. These dehydrogenations of alcohols to aldehydes and ketones require refluxing or distillations and have given way to dimethyl sulfoxide oxidations, which take place at room temperature. 

Selenoacetals are readOy available compounds which have been prepared (i) by selenoacetalization of carbonyl compounds with selenols - in acidic media, with tris seleno)boranes > in neutral or acidic media or with trimethylsilyl selenides and aluminum trichloride (Schemes 69 and... 

Aluminum tris(2,6-diplienylphenoxide) (ATPH), an aluminum-based Lewis acid with bulky substituents, is valuable as an extremely selective activator of less hindered aldehyde carbonyls (Scheme 10.8) [36]. In competitive aldol reactions of two different aldehydes, more fhan one equivalent of ATPH achieves highly chemoselective functionalization of less hindered aldehydes. Unfortunately, catalytic use of ATPH reduces the chemical yield and chemoselectivity. In contrast, a catalytic quantity of aluminum bis(trifluoromethanesulfonyl)amide 13 can promote the chemoselective aldol reaction. 

Scheme 2.128 Reaction of l /le3SiCF3 with a variety of carbonyl compounds (ATPH = aluminum tri(2,6-bis(tert-butyl)phenoxide) [64b, 65, 73].

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