DIBAH hydride

A third method of aldehyde synthesis is one that we ll mention here just briefly and then return to in Section 21.6. Certain carboxylic acid derivatives can be partially reduced to yield aldehydes. The partial reduction of an ester by dhsobutylaluminum hydride (DIBAH), for instance, is an important laboratory-scale method of aldehyde synthesis, and mechanistically related processes also occur in biological pathways. The reaction is normally carried out at —78 °C (dry-ice temperature) in toluene solution. 

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

Hayashi, M., Yoshiga, T., Nakatani, K. et al. (1994) Reduction of or-trialkylsiloxy nitriles with diisobutylalu-minium hydride (DIBAH) a facile preparation of (t-lrialkylsiloxy aldehydes and their derivatives. Tetrahedron, 50, 2821-2830. 

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). 

Scheme 2.46 Synthesis of natural products by reduction of propargylic electrophiles with aluminum hydrides. DIBAH = diisobutylaluminum hydride ...

Scheme 18.13 Synthesis of the grasshopper ketone (34) according to Eugster and co-workers [46d] (DIBAH = diisobutylaluminum hydride).

Recently, diisobutylaluminium hydride (DIBAH) was found to be a selective reducing agent in the reduction of steroidal 5,7 and 22,24(28) dienes (equation 32)100. 

TIBA = tris-iso-butylaluminium DIBAH = di-iso-butylaluminium hydride BEM = n-butylethylmagnesium. xs = excess (3mmol L" ). 

Aldehydes are prepared by the hydroboration-oxidation of alkynes (see Section 5.3.1) or selective oxidation of primary alcohols (see Section 5.7.9), and partial reduction of acid chlorides (see Section 5.7.21) and esters (see Section 5.7.22) or nitriles (see Section 5.7.23) with lithium tri-terr-butox-yaluminium hydride [LiAlH(0- Bu)3] and diisobutylaluminium hydride (DIBAH), respectively. 

Primary and tertiary alcohols are obtained conveniently from esters by the reduction of LiAlH4 and two molar equivalents of organometallic reagents (R MgX or R Li), respectively (see Sections 5.7.22 and 5.5.5). A less powerful reducing agent, diisobutylaluminium hydride (DIBAH), reduce an ester to an aldehyde (see Section 5.7.22). 

Sterically bulky reducing agents, e.g. diisohutylaluminium hydride (DIBAH), can selectively reduce esters to aldehydes. The reaction is carried out at low temperatures (—78 °C) in toluene. Diisohutylaluminium hydride has two bulky isobutyl groups, which make this reagent less reactive than LiAlH4. 

Reduction of attenes.1 DIBAH preferentially reduces the more substituted double bond of an allene. Actually the hydride may attack the less substituted double bond and an allylic rearrangement during hydrolysis may be involved. The reduction of 1,1-diphenylallene2 follows a different course, but may represent a special case. 

Titanium(III) chloride-Diisobutylaluminum hydride. A black, solid lower-valent titanium reagent (1) is obtained on reduction of TiCl3 3THF with DIBAH in toluene.1... 

Recently, Schwartz and Shoer have described the use of (C5H5)2ZrCl2 as a catalyst in the reduction of CO by diisobutylaluminum hydride (DIBAH) (81). The products of this reaction, after aqueous acid workup, were methanol, ethanol, 1-propanol, and 1-butanol in decreasing amounts. A labeling... 

Dissociation of DIBAH from (16) then creates a vacant site for CO coordination. Hydride migration from Zr or external attack by hydride from DIBAH leads to the formation of a formyl that is then reduced by the aluminum hydride species (81). The steps for chain propagation and termination are outlined below. Since the exact nature of the Zr and A1 species is unknown in these steps, they are represented by (Zr) and (Al), respectively. 

Numerous reducing agents were tried at this point unsuccessfully. For example, lithium aluminum hydride destroyed the substrate, whereas DIBAH or lithium borohydnde in THF and sodium borohydride in ethanol led to reduction of the quinoline system. On the other hand, both potassium borohydride (either with or without 18-crown-6) and zinc borohydride (with or without ethanol) produced no reaction at all. Lithium triethylborohydride resulted in de-methoxylation, and sodium borohydride in refluxing THF gave a 45% yield of diol 16 together with overreduced product. 

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