Diisobutylaluminum

The conversion of carboxylic acid derivatives (halides, esters and lactones, tertiary amides and lactams, nitriles) into aldehydes can be achieved with bulky aluminum hydrides (e.g. DIBAL = diisobutylaluminum hydride, lithium trialkoxyalanates). Simple addition of three equivalents of an alcohol to LiAlH, in THF solution produces those deactivated and selective reagents, e.g. lithium triisopropoxyalanate, LiAlH(OPr )j (J. Malek, 1972). 

Triisobutylalurninum is converted to diisobutylalurninum chloride [1779-25-5] and diisobutylaluminum hydroxide [1191 -15-7] which are used as... 

CH2=C(OBn)(CH3), POCI3 or TsOH, 61-98% yield. It should be noted that these conditions do not afford a cyclic acetal with a 1,3-diol. This ketal is stable to LiAlH4, diisobutylaluminum hydride, NaOH, alkyllithiums, and Grignard reagents. 

Me2CHCH2)2AlH, PhCH3, —78°, 80% yield. Since the /V-benzoyl group in this substrate could not be removed by hydrolysis, a less selective reductive cleavage with diisobutylaluminum hydride was used. 

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

Mono MOM derivatives of diols can be prepared from the ortho esters by diisobutylaluminum hydride reduction (46-98% yield). In general, the most hindered alcohol is protected. ... 

Diazoquinone-novolac resist, 506 Diazotization reaction, 941 DIBAH, see Diisobutylaluminum hydride... 

Digitoxigenin, structure of, 1097 Digitoxin, structure of, 989 Dihalide, alkynes from, 261 Dihedral angle, 94 Diiodomelhane. Simmons-Smith reaction with, 228-229 Diisobutylaluminum hydride, reaction with esters, 812 structure of, 699 Diisopropylamine, pK.d of, 923 1,3-Diketone, pfCa of, 852 Dimethyl disulfide, bond angles in, 20 structure of, 20 Dimethyl ether, electrostatic... 

The present method of preparing 2-cyclohexyloxyethanol has been described before,6 but on a smaller scale. Other /3-hydroxy ethers6 and /3-hydroxy thio ethers 8 can be prepared by the same method. Hydrogenolysis of the C—O bond in acetals has also been reported7 with diisobutylaluminum hydride for example, 2-cyclohexyloxyethanol was obtained in 91% yield in this manner. 

The isomerization of an allylic amine to an enamine by means of a formal 1,3-hydrogen shift constitutes a relatively small structural change. However, this transformation could be extremely valuable if it could be rendered stereoselective. In important early studies, Otsuka and Tani showed that a chiral cobalt catalyst, prepared in situ from a Co(ii) salt, a chiral phosphine, and diisobutylaluminum hydride (Dibal-H), can bring about the conversion of certain pro-chiral olefins to chiral, isomeric olefins by double bond migra-... 

TV-aluminum imines are another example of masked inline derivatives of ammonia. They are easily synthesized by partial reduction of nitriles with diisobutylaluminum hydride (D1BAL-H)6. Addition of lithium organic reagents to /V-aluminum iniines 7 derived from O-protected cyanohydrins 6 provides a-amino alcohols 8a and 8b in moderate yields and low to good diastereo-selectivities n 12. 

Diisobutylaluminum hydride (DIBAL-H) can also be used for partial reduction of cyclic imides37. Although less convenient than sodium borohydride, an important synthetic aspect is the fact that in the reduction of asymmetrically substituted imides, diisobutylaluminum hydride and sodium borohydride may show opposite regioselectivity38,39. 

A more general route to 4-acetoxy-l,3-dioxanes utilizes the reductive acylation of l,3-dioxane-4-ones [46] (Scheme 21). l,3-Dioxane-4-ones 126 are prepared from the corresponding -hydroxy carboxylic acids. Low temperature reduction with DIBALH generates a diisobutylaluminum hemiacetal (127) which undergoes acylation in situ with AC2O in the presence of pyridine and DMAP. This method allows for the preparation of a wide range of 4-acetoxy-l,3-dioxanes, without the problem of a-epimerization. This method also represents a general approach to acylic a-acetoxy ethers, which are themselves useful synthetic intermediates [47,48]. 

Scheme 10. Synthesis of the ds-donor-acceptor-substituted TEE 86 [ 100]. DIBAL-H diisobutylaluminum hydride, PCC pyridinium chlorochromate, LDA lithium diisopropylamide...

The crucial cyclization of 129 was accomplished by oxidation with pyri-dinium chlorochromate (PCC) and acetylation, providing two cyclohexane derivatives (130 and 131) in the ratio of 10 1. Thermal decarboxylation of 130 resulted in formation of the cyclohexene derivative 132, with concomitant elimination. Reduction of the ester group with diisobutylaluminum hydride converted 132 into 133. Hydroboration-oxidation of 133 gave the carba-sugar derivative 134 as a single product. 

Starting from 149, novel carba-sugar pentaacetates of the P-L-allo (168) and a-u-manno (171) configuration have been synthesized. Reduction of 149 with diisobutylaluminum hydride (DIBAL-H) and acetylation gave a mixture of acetates 162 and 163. Hydroxylation of the mixture with osmium tetraoxide and hydrogen peroxide provided compounds 164 and 165 in the ratio of 9 1. Hydrolysis of 164 gave compound 166, which was transformed into 168 by a reaction analogous to that employed in the preparation of 157 from 153. 

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