Methylaluminum bis

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). 

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

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). 

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). 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

T. Ooi, K. Maruoka, and H. Yamamoto 95 REARRANGEMENT OF trans-STILBENE OXIDE TO DIPHENYL-ACETALDEHYDE WITH CATALYTIC METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE)... 

Methylaluminum bis(4-bromo-2,6-di-tert-butyiphenoxide) Aluminum, bis[4-bromo-2,6-bis(1,1-dimethylethyl)phenolato]methyl- (12) (118495-99-1)... 

The metalloporphyrin-initiated polymerizations are accelerated by the presence of steri-cally hindered Lewis acids [Inoue, 2000 Sugimoto and Inoue, 1999]. The Lewis acid coordinates with the oxygen of monomer to weaken the C— O bond and facilitate nucleophilic attack. The Lewis acid must be sterically hindered to prevent its reaction with the propagating center attached to the prophyrin structure. Thus, aluminm ortho-substituted phenolates such as methylaluminum bis(2,6-di-/-butyl-4-methylphenolate) accelerate the polymerization by factors of 102-103 or higher. Less sterically hindered Lewis acids, including the aluminum phenolates without ortho substituents, are much less effective. 

A synthetic application is demonstrated by Tanino and his co-workers who reported a total synthesis of ingenol 14 using this methodology.Use of methylaluminum bis(2,6-dimethyl-4-nitrophenoxide) promoted both cyclization and following rearrangement reactions smoothly to construct an ingenane skeleton 15 (Scheme 2). 

In addition to MMA, a variety of methacrylic esters were polymerized rapidly to the corresponding polymers with narrow MWDs in the presence of methylaluminum bis(2-ferf-butyl-4-methoxyphenolate) (3c). The successful examples include ethyl methacrylate (EMA), isopropyl methacrylate ( °PMA), n-butyl methacrylate ("BMA), isobutyl methacrylate ( °BMA), benzyl methacrylate (BnMA), and dodecyl methacrylate (Cj2MA), where the Mn values were all close to the predicted values (Mn j ) with the Mw/Mn ratios below 1.1 (Table 3, runs 1-4,6,7). The polymerization of ferf-butyl methacrylate ( BMA) is the only exception, where the monomer conversion hardly increased even after 24 h. 

Fig.1. Two-stage polymerization of methyl methacrylate (MMA) in CH2CI2 at room temperature with the enolatealuminum porphyrin (2, R=Me)-methylaluminum bis(2,4,6-tri-tert-butylphenolate) (3f) (1.0 1.0) system. GPC profiles of the polymers formed at the first stage (I) [MMA]o/[l (X=Me)]o=50, 100% conversion Mn=7,000, Mw/Mn= 1.12 and the second stage (II) [MMA]o/[2]q=200, 100% conversion Mn=47,600,Mw/Mn= 1.05...

Table 3. Polymerization of methacrylic esters via enolatealuminum porphyrins 2 in the presence of methylaluminum bis(2-tert-butyl-4-methoxyphenolate) (3c) ...

Fig. 7. NMR spectra in CD2CI2 at 25 °C of A Methyl methacrylate (MMA) and B An equimolar mixture of MMA and methylaluminum bis(2,4,6-tert-butylphenolate) (3f)...

Fig. 16. NMR profiles in CD2CI2 at 25 °C of methyl methacrylate (MMA)-Lewis acid mixtures. Relationships between the chemical shift of the C=0 signal of MMA and the mole ratio of Lewis acid to MMA Lewis acids triphenylboron ( ), tris(pentafluorophenyl)boron ( ), tri-n-butylboron (A), triphenylaluminum (O), and methylaluminum bis(2,4,6-tri-tert-butylphenolate) ( )...

Fig. 18. NMR spectrum in CDCI3 of the poly(methyl methacrylate) (MnGpc=6900, Mw/Mn=1.13) obtained with the (TPP)AlSPr (1, X=SPr)-methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) system. [MMA]o/[l]o/[3e]o=30/1.0/0.5,100% conversion...

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