Question

Discuss various methods of reduction of esters?giving the product formed?

Answer 1

Answer:

1) Esters are normally reduced by reaction with lithium aluminum hydride to alcohols. For example

$$\begin{array}{c} \mathrm{CH_3-C-O-CH_2-CH_2-CH_3} \\ \text{propyl ethanoate} \end{array} \quad \begin{array}{c} 1. \mathrm{LiAlH_4} \\ \text{ether} \\ 2. \mathrm{H_3O^+} \end{array} \quad \begin{array}{c} \mathrm{CH_3-CH_2-OH} \\ \text{ethanol} \end{array} \quad + \begin{array}{c} \mathrm{CH_3-CH_2-CH_2-OH} \\ \text{propanol} \end{array}$$

2) Also was founded abstract where a novel one-pot procedure for a directly reductive conversion of esters to the corresponding ethers by $\mathrm{Et_3SiH}$ in the presence of a catalytic amount of $\mathrm{InBr_3}$ is described. This simple catalytic system appeared to be remarkably tolerant to several functional groups.

$$\begin{array}{c} 5 \mathrm{mol}\cdot\% \mathrm{InBr_3} \\ 4 \mathrm{eq.}\ \mathrm{Et_3SiH} \\ \mathrm{CHCl_3,\ 60^\circ C,\ 1-6\ h} \end{array} \quad \begin{array}{c} \mathrm{R^+O^-R^-} \\ \mathrm{R: alkyl, benzyl} \\ \mathrm{R': alkyl, benzyl} \end{array}$$

3) Esters can be reduced to aldehydes with diisobutylaluminum hydride (DIBAL), a bulky source of hydride ion

Example 1: Reduction of esters to aldehydes

Low temperature is important to prevent further reduction

4) In the Fukuyama reduction, a carboxylic acid is first converted to a thioester through addition of a thiol (with a mechanism similar to esterification). The thioester is then reduced to an aldehyde by a silyl hydride with a palladium catalyst.

$$\begin{array}{c} \mathrm{O} \\ | \\ \mathrm{R^+OH} \end{array} \quad \begin{array}{c} \mathrm{HS-R} \\ | \\ \mathrm{R^+S^+R^-} \end{array} \quad \begin{array}{c} \mathrm{O} \\ | \\ \mathrm{R^-S^+R^-} \end{array} \quad \begin{array}{c} \mathrm{SiHEt_3} \\ | \\ \mathrm{Pd/C} \\ \end{array} \quad \begin{array}{c} \mathrm{O} \\ | \\ \mathrm{R^-O^-} \end{array}$$

5) In the Weinreb reaction, an acyl chloride is first converted to the Weinreb amide, then treated with an organometallic reagent to form a ketone, or lithium aluminum hydride to form an aldehyde

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