Diisobutylaluminum hydride DIBAL

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-... 

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. 

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. 

An alternative access to murrayanine (9) was developed starting from the mukonine precursor 609. The reduction of the ester group of 609 using diisobutylaluminum hydride (DIBAL) afforded the benzylic alcohol 611. In a one-pot reaction, using very active manganese dioxide, 611 was transformed to murrayanine (9) (574) (Scheme 5.36). 

Diisobutylaluminum hydride DIBAL-H Aluminum, hydrodiisobutyl- (8) Aluminum, hydrobis(2-methylpropyl)- (9) (1191-15-7)... 

The other stereoselective synthesis/281 shown in Scheme 8, foresees conversion of Boc-L-Asp-OtBu 20 into the related (3-aldehyde 22 via the Weinreb amide 21 and its reduction with diisobutylaluminum hydride (DIBAL-H). Wittig condensation of 22 with the ylide derived from (3-carboxypropyl)triphenylphosphonium bromide using lithium hexamethyldisilaza-nide at —78 to 0°C, produces the unsaturated compound 23 which is catalytically hydrogenated to the protected L-a-aminosuberic acid derivative 24. Conversion of the co-carboxy group into the 9-fluorenylmethyl ester, followed by TFA treatment and reprotection of the M -amino group affords Boc-L-Asu(OFm)-OH (25). 

Recent efforts in the area of Friedel-Crafts alkylations have focused on the direct introduction of alkyl groups bearing functionalities, and on intramolecular alkylative cycliz-ations. The cyclization of the 2-substituted thiophene (55) to (56) has been achieved in 65% yield (80JOC3159). Similarly, the 3-substituted thiophene (57) has been cyclized to the isomeric (58). In both cases, detosylation of the product was achieved by treatment with diisobutylaluminum hydride (DIBAL). An elegant bis-cyclization of the diene (59) to the octahydrodibenzothiophene (60) has been reported (70CJC2587). 

Several synthetic methods for the reduction of a-amino esters have also been reported. The reduction of methyl or ethyl esters by diisobutylaluminum hydride (DIBAL-H) at low temperature (—78 °C) has been described as useful for the preparation of a-amino aldehydes. 1118 20 Again, this method suffers from overreduction. Reductive methods involving mild reductive agents have been described. The reduction of phenyl esters 6 21 (readily prepared from the corresponding amino acid 5) with lithium tri-ferf-butoxyaluminum hydride is efficient for the preparation of various Boc-a-amino aldehydes including Na-Boc-7V J-nitroargininal and A7a-Boc-W"-Z-argininal (Scheme 5). 

The Homer-Emmons addition of dialkyl carboalkoxymethylenephosphonates to aldehydes [22] has been widely used to generate a,p-unsaturated esters which, in turn, can be reduced to allylic alcohols. Under the original conditions of the Homer-Emmons reaction, the stereochemistry of the oc,(3-unsaturated ester is predominantly trans and therefore the trans allylic alcohol is obtained upon reduction. Still and Gennari have introduced an important modification of the Homer-Emmons reaction, which shifts the stereochemistry of the a,[i-unsaturated ester to predominantly cis [23], Diisobutylaluminum hydride (DIBAL) has frequently been used for reduction of the alkoxycarbonyl to the primary alcohol functionality. The aldehyde needed for reaction with the Homer-Emmons reagent may be derived via Swern oxidation [24] of a primary alcohol. The net result is that one frequently sees the reaction sequence shown in Eq. 6A. 1 used for the net preparation of 3E and 3Z allylic alcohols. 

Step 2a Utilization of 1 eq of diisobutylaluminum hydride (DIBAL-H) ensures reduction of the ester group stops to the corresponding aldehyde. 

Diisobutylaluminum hydride (DIBAL-H) reduces esters directly to aldehydes at dry ice temperature, about -78 °C. Unlike LiAlH4 (which reduces esters to primary alcohols), cold DIBAL-H usually does not reduce the aldehyde further. The initial reaction forms an aluminum complex that is stable toward further reduction, but hydrolyzes to the aldehyde in the aqueous workup. 

Acid chlorides are more reactive than other acid derivatives, and they are reduced to aldehydes by mild reducing agents such as lithium tri-ferf-butoxyaluminum hydride. Diisobutylaluminum hydride (DIBAL-H) reduces esters to aldehydes at low temperatures, and it also reduces nitriles to aldehydes. These reductions were covered in Sections 18-9,18-10, and 20-13. 

Asymmetric reduction of (5s)-sulfmimine 110 with diisobutylaluminum hydride (DIBAL) afforded a diastereomeric mixture of sulfinamides 111 in 92% yield and in a ratio of 96 4.34 Use of sodium boron hydride, lithium aluminum hydride, or lithium alkoxyaluminum hydride resulted in lower optical yields.33,34,75 The sul-finyl group can be removed by treating 111 with trifluoroacetic acid (TFA) and methanol to give a-phenylethyl amine (112). 

Hydride reductions of (7) can be controlled to give either the (R) or (5) secondary hydroxy compound with good selectivity by choice of the reducing agent. Lithium Tri-s-butylborohydride (L-Selectride ) provided the (5)-alcohol (according to Cram s chelate rule) and Diisobutylaluminum Hydride (DIBAL) gave the (R)-carbinol in excess (eq 7). The DIBAL results were rationalized in terms of the open-chain Comforth dipole model. ... 

Diisobutylaluminum hydride (DIBAL-H) hydrogenolyzes simple ortho esters to acetals at room temperature and reduces acetals and ketals to ethers at 70-80 °C (equation 6) benzyl ethers are cleaved at still higher temperatures. This reagent shows good selectivity and considerable versatility. It has been used to reduce acetals of formaldehyde (equation 7), ° which few other reagents can accomplish. With catechol ketals a single reductive cleavage occurs at room temperature (equation 8). ... 

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