Meerwein–Ponndorf–Verley reduction

Of the Meerwein - Ponndorf - Verley reduction refers to the reduction of aldehydes and ketones to alcohols with aluminum isopropoxide in isopropanol as a solvent. The reaction is an equilibrium reaction, the reverse reaction is known as the Oppenauer oxidation. The reaction takes place at the carbonyl groups under very mild conditions and selective. Enolizable aldehydes and ketones, β -keto esters and β -diketones can not be reduced to the Meerwein - Ponndorf - Verley reduction. The reaction is named after their discoverers, Hans Meerwein, Wolfgang Ponndorf and Albert Verley.

Mechanism

2 reacts with the carbonyl compound of aluminum isopropoxide 1 via a cyclic six-membered transition state 3, the aluminum acts as a Lewis acid, whereby the complexation is carried out of the carbonyl oxygen, which facilitates reduction in the time required for the hydride. Elimination of acetone 4, the aluminum alkoxide formed as an intermediate is formed 5 This reacts with the solvent ( isopropanol) 6 with re-formation of the Aluminiumisopropanolats 1, which thus acts as a catalyst to the corresponding alcohol 7

The equilibrium of this reaction is shifted by distilling the resulting acetone 4 to the right side. The reversal of the Meerwein - Ponndorf - Verley reduction, the Oppenauer oxidation, but which has little preparative importance.

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