Methylaluminum

Precomplexation of 2-butylcyclopentanone with methylaluminum bis(2,6-di-hrt-butyI-4-methylphenoxide) (MAD), prior to the addition of methyllithium, leads to the exclusive formation of the equatorial alcohol via cis attack3 4. However, this methodology is apparently not applicable to 3-substituted cyclopentanones. Thus, addition of propylmagnesium bromide to... 

As well as the modified cuprate reagents, Grignard reagents in the presence of the highly sterically demanding methylaluminum bis(2,4,6-tri-fcrr-butylphenoxide) (MAT, 8) also show considerable anti-Cram selectivity35 36 (Table 9). 

To 158 mg (1 mmol) of 2-formyl-jVJV,3-trimcthylbutanamide in 5 ml, of CH2C12 are added at 0°C 2 mL of 1.0 M (dichloro)methylaluminum (2 mmol) in hexane. The reaction mixture is stirred at 25 °C for 2 h, then quenched with 1 M HC1. After extraction with CHCI,/EtOH (3 1), the combined organic layer is dried over Na,So4 and concentrated in vacuo. The crude product is purified by silica gel column chromatography yield 106 mg (62%) d.r. [(26, 35 )/(25, 3R )] 99 1 (determined by capillary GC). 

Methylaluminum Diazide. CH3A1(N3)2, mw 126.08, N 66.67%, white powd. When a frozen eth soln of A1(CH3)3 and excess HN3 is thawed, reaction begins at room temp with evolution of CH4 and pptn of a fine white powd, methyl-aluminum diazide. The reaction is completed... 

Lithium cyclohexylisopropylamide Lithium diisopropylamide Lithium hexamethyl disilazide Lithium 2,2,6,6-tetramethylpiperidide Methylaluminum I ij-(4-bromo-2,6-di-tert-butylphenoxide) I (s-(2,6-di-t-butyl-4-methylphenoxy)methyl aluminum mefa-Chloroperoxybenzoic acid Methyl... 

MABR Methylaluminum bis-(4-hYomo-2,6-di-tert-buiy phenoxidc) ... 

Lewis acids such as zinc chloride, boron trifluoride, tin tetrachloride, aluminum chloride, methylaluminum dichloride, and diethylaluminum chloride catalyze Diels-Alder reactions.22 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the addition is believed to be concerted and enhanced regio- and stereoselectivity is often observed.23... 

Entry 8 uses a to-trifluoromethanesulfonamido chelate of methylaluminum as the catalyst. As in Entry 6, the use of a 3,5-dimethylphenyl group in place of phenyl improved enantioselectivity. The ortho-methylphenyl substituent on the maleimide dienophile restricts the potential coordination sites at the metal center. NMR characterization of the reactant-catalyst complex suggests that reaction occurs through the TS shown below. 

Denmark and coworkers have found that methylaluminum bis (2,6-di-tert-butyl-4-methyl-phenoxide) (MAD) or methylaluminum bis(2,6-diphenylphenoxide) (MAPh) is effective as the Lewis acid promoter for cycloaddition of 2,2-disubstituted 1-nitroalkenes (Eq. 8.100).158 Other Lewis acids such as SnCl4, TiCl4, and TiCl2(Oi-Pr)2 fail to promote the cycloaddition of 2,2-disubstituted 1-nitroalkenes. The products are converted into 3,3-disubstituted pyrrolidines via hydrogenolysis.158 Reductive cleavage of N-0 bonds produces oxime hemiacetals, which are further reduced to amido aldehydes and finally to pyrrolidines. This reaction provides a useful synthetic method for pyrrolidines, which is discussed later. 

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... 

Rearrangement of trans-Stilbene Oxide to Diphenylacetaldehyde with Catalytic Methylaluminum Bis(4-bromo-2,6-di-tert-butylphenoxide). 

In 1985, Eisch et al. isolated a cationic alkenyltitanium complex (55) by the insertion of an alkyne into the cationic Ti-C bond generated from titanocene dichloride and methylaluminum dichloride (Eq. 2) [77], Similarly, a mixture of Cp2TiCl(CH2SiMe3) and A1C13 afforded the solvent-separated ion pairs,... 

Microwave heating has also been employed for performing retro-Diels-Alder cycloaddition reactions, as exemplified in Scheme 6.94. In the context of preparing optically pure cross-conjugated cydopentadienones as precursors to arachidonic acid derivatives, Evans, Eddolls, and coworkers performed microwave-mediated Lewis acid-catalyzed retro-Diels-Alder reactions of suitable exo-cyclic enone building blocks [193, 194], The microwave-mediated transformations were performed in dichloromethane at 60-100 °C with 0.5 equivalents of methylaluminum dichloride as catalyst and 5 equivalents of maleic anhydride as cyclopentadiene trap. In most cases, the reaction was stopped after 30 min since continued irradiation eroded the product yields. The use of short bursts of microwave irradiation minimized doublebond isomerization. 

Table 4 Ethylene polymerization results for Zr-FI catalysts 1 and 31 with MAO or MAO/tri-methylaluminum (TMA)... 

Reaction of 3 with 1 equivalent of a phosphine results in formation of "phosphine-modified catalysts (4). The complex formed from 7r-allyl-nickel chloride, tricyclohexylphosphine, and methylaluminum dichloride (4a) has been isolated and its structure determined crystallographically (see Fig. 1) (57) The phosphine is bonded to the nickel atom, and interaction with the Lewis acid takes place via a chlorine bridge. The bridging chlorine atom is almost symmetrically bound to both the nickel... 

Selective reduction of ketones.1 This reagent can be used to effect selective reduction of the more hindered of two ketones by DIBAH or dibromoalane. Thus treatment of a 1 1 mixture of two ketones with 1-2 equiv. of 1 results in preferential complexation of the less hindered ketone with 1 reduction of this mixture of free and complexed ketones results in preferential reduction of the free, originally more hindered, ketone. An electronic effect of substituents on a phenyl group can also play a role in the complexation. This method is not effective for discrimination between aldehydes and ketones, because MAD-complexes are easily reduced by hydrides. MAD can also serve as a protecting group for the more reactive carbonyl group of a diketone. The selectivity can be enhanced by use of a more bulky aluminum reagent such as methylaluminum bis(2-f-butyl-6-( 1,1-diethylpropyl)-4-methylphenoxide). 

Selective alkylation of ketonesThis reagent forms a complex so much more rapidly with aldehydes than with ketones that selective alkylation of a keto group in the presence of an aldehyde group with an alkyllithium or Grignard reagent is possible. The opposite chemoselectivity is achieved with the bulky methylaluminum bis(2,6-di-f-butyl-4-phenoxide) (MAD, 13, 203 this volume). 

The reaction of Me3Al with excess trimethylsilylcyanide under reflux produced methylaluminum dicyanide CH3A1(CN)2 as an off-white powder.142 No X-ray crystal structure was reported however, the IR showed the presence of both bridging and terminal cyanide groups in the compound. 

Lithium aluminum hydride Lithium hydride Methyl isocyanate Methylaluminum sesquibromide Methylaluminum sesquichloride Methyldichlorosilane Methylene diisocyanate Methylpentaldehyde Methyltrichlorosilane Mono-(trichloro)-tetra-(mono-potassium dichloro)-penta-s-triazinetrione, dry Monochloro-s-triazinetrione acid Octadecyltrichlorosilane Phenyl trichlorosilane Phosphorus oxychloride Phosphorus pentachloride Phosphorus pentasulfide... 

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