DIBAL reducing agent

Solladie later proposed the now favoured explanation of intramolecular hydride transfer from the DIBAL reducing agent in the absence of a chelating metal... 

Dibal IS an informal name given to the organometallic compound [(CH3)2CHCH2l2AlH used as a reducing agent m certain reactions Can you figure out the systematic name from which dibal IS denved" ... 

The other way of reducing nitriles to aldehydes involves using a metal hydride reducing agent to add 1 mol of hydrogen and hydrolysis, in situ, of the resulting imine (which is undoubtedly coordinated to the metal). This has been carried out with LiAlH4, LiAlH(OEt)3, LiAlH(NR2)3, and DIBAL-H. The metal hydride method is useful for aliphatic and aromatic nitriles. 

When the reducing agent is DIBAL-H, the product is a secondary amine, arising from a rearrangement ... 

The catalytic cycle with Ni catalysts is generally similar. The essential difference is the deactivation process, which in this case occurs not via the formation of a precipitate of Ni°, but rather due to interception of the highly reactive Ni° species by any fortuitous oxidant, such as oxygen. As Ni11 is not so easily reduced to Ni° as Pdn is to Pd°, Ni-catalyzed systems often require the addition of a stoichiometric reducing agent (Zn, DIBAL-H, other hydride transfer agents, BuLi, etc.). 

Lautens and Rovis showed that the rate of addition of the reducing agent DIBAL had a significant effect on the reactions. Fast addition of the DIBAL (addition time to 7 min this raised the ee to 82% (entry 2, Table 11). The optimal addition time was found to be 1 h which gave the cyclohexenol 121 with 97% ee (entry 3, Table 11). It was possible to reduce the amount of catalyst to l-2mol%. 

The reduction of acetylenic tellurides to the vinylic ones is achieved by treatment with NaBH4 in EtOH. The formal unusual reduction of the carbon triple bond by NaBH4 can be rationalized involving the attack of a hydride ion to the tellurium atom producing a tellurol and an acetylenic anion followed by the addition of the tellurolate anion to the acetylene, DIBAL-H has later been employed as a reducing agent. ... 

Reduction of hydroxy lactams (154) with a complex of DIBAL and butyl-lithium gave an inseparable mixture of perhydropyrido[2,l-b][l,3]oxazines (155) (92TL507). When Red-Al was used as a reducing agent, side products... 

Hyperforin is not reduced by sodium borohydride. Reduction with hydride-transfer reagents such as lithium aluminium hydride (LAH), RED-AL, and DIBAL-H, gave varied products in good yields. Its two dicarbonyl systems are amenable to reduction or deoxygenation upon treatment with alane reducing agents and pave the way to new and interesting modifications of the natural product.301... 

Reduction by mild reducing agents converts acyl chlorides, esters, and nitrites into aldehydes. The reducing agents of choice are usually lithium tri-tert-butoxy aluminum hydride (LATB—H) and diisobuty-laluminum hydride (DIBAL—H). Following are the structures for these compounds ... 

Earlier, CI2Pd(PPh3)2 was reduced with two molar equivalent of DIBAL-H in hexane. It has since been shown that the use of a reducing agent is unnecessary. 

A similar mechanism is operative in the reduction of carboxylic esters with DIBAL (Figure 17.61). The tetrahedral intermediate A is formed by addition of an A1—H bond of the reducing agent to the ester C=0 bond. This tetrahedral intermediate A does not necessarily decompose immediately to an aldehyde and ROAl(iBu)2. In nonpolar media, A definitely decomposes quite slowly. In fact, at very low temperatures A remains unchanged until it is protonated to a hemiacetal during aqueous workup. The latter eliminates water to give the aldehyde. 

The two reducing agents considered so far in this section—LiAlH4 and DIBAL—also are the reagents of choice for the reduction of nitriles (Figure 17.64). The mechanistic details of these reactions can be gathered from the figure, and the result can be summarized as follows. 

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. 

Two isobutyl groups are present in the reducing agent diisobutyl aluminium hydride (DIBAL). 

DIBAL is in some ways like borane—it exists as a bridged dimer, and it becomes a reducing agent only after it has formed a Lewis acid-base complex, so it too reduces electron-rich carbonyl groups most rapidly. DIBAL will reduce esters even at -70 °C, and at this temperature the tetrahedral intermediate may be stable. Only in the aqueous work-up does it collapse to the aldehyde when excess DIBAL has been destroyed so that no further reduction is possible. 

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. ... 

UAIH4 is a strong reducing agent. DIBAL-H and LiAIH[OC(CH3)3]3 are milder, more selective reducing agents. 

A milder reducing agent (DIBAL-H or LiAIH[OC(CH3)3j3) converts RCOCI or RCOOR to RCHO at low temperatures. 

With milder reducing agents such as DIBAL-H and LiAlH[OC(CH3)3]3, the process stops after reaction with one equivalent of Hr and the aldehyde is formed as product. With a stronger reducing agent like LiAlH4, two equivalents of H are added and a 1° alcohol is formed. 

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