Meerwein-Verley- Ponndorf

To meet the needs of the advanced students, preparations have now been included to illustrate, for example, reduction by lithium aluminium hydride and by the Meerwein-Ponndorf-Verley method, oxidation by selenium dioxide and by periodate, the Michael, Hoesch, Leuckart and Doebner-Miller Reactions, the Knorr pyrrole and the Hantzsch collidine syntheses, various Free Radical reactions, the Pinacol-Pinacolone, Beckmann and Arbusov Rearrangements, and the Bart and the Meyer Reactions, together with many others. 

The Meerwein-Ponndorf-Verley procedure has largely been replaced by reduction procedures that use lithium aluminum hydride, sodium borohydride or derivatives thereof. The Meerwein-Ponndorf-Verley reduction however has the advantage to be a mild and selective method, that does not affect carbon-carbon double or triple bonds present in the substrate molecule. 

The lithium aluminum hydride-aluminum chloride reduction of ketones is closely related mechanistically to the Meerwein-Ponndorf-Verley reduction in that the initially formed alkoxide complex is allowed to equilibrate between isomers in the... 

Sandmeyer reaction, 943 saponification. 809-810 SN1 reaction, 373-375 Sn2 reaction, 363-364 Stork enamine reaction, 897-898 transamination, 1167 Williamson ether synthesis, 655 Wittig reaction, 720-721 Wolff-Kishner reaction, 715-716 Meerwein-Ponndorf-Verley reaction, 746... 

Die stabilen Alkohole konnen hier ebenfalls durch Meerwein-Ponndorf-Verley-Reduktion hergestellt werden7. 

Die gebildeten Dichloraluminium-alkanolate sind ahnlich wie bei der Meerwein-Ponndorf-Verley-Reduktion ebenfalls zum Hydrid-Transfer geeignet3 ... 

Very recently the Meerwein-Ponndorf-Verley-Oppenauer (MPVO) reaction has been exploited for the racemization of alcohols using inexpensive aluminum-based catalysts. Combination of these complexes with a lipase (CALB) results in an efficient DKR of sec-alcohols at ambient temperature. To increase the reactivity of the aluminum complexes, a bidentate ligand, such as binol, is required. Also, specific acyl donors need to be used for each substrate [31] (Eigure 4.9). 

Smis assisted version of this reduction has been reported. The Meerwein-Ponndorf-Verley reaction usually ... 

The Oppenauer Oxidation. When a ketone in the presence of base is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation. This is the reverse of the Meerwein-Ponndorf-Verley reaction (16-23), and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum r r/-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the... 

Secondary alcohols may be oxidised to the corresponding ketones with aluminium /erl.-butoxide (or tsopropoxide) in the presence of a large excess of acetone. This reaction is known as the Oppenauer oxidation and is the reverse of the Meerwein - Ponndorf - Verley reduction (previous Section) it may be expressed ... 

Catalyzed hydrogen transfer from a hydrogen donor other than H2 is attractive industrially because of safety, engineering and economic concerns (1). This reaction has been extensively studied in the homogeneous phase (2) and under Meerwein-Ponndorf-Verley conditions (3). 

The Michael addition/Meerwein-Ponndorf-Verley (MPV) reduction sequence developed by Node and coworkers is another easily implementable strategy for the... 

Zr compounds are also useful as Lewis acids for oxidation and reduction reactions. Cp2ZrH2 or Cp2Zr(0 Pr)2 catalyze the Meerwein-Ponndorf-Verley-type reduction and Oppenauer-type oxidation simultaneously in the presence of an allylic alcohol and benzaldehyde (Scheme 40).170 Zr(C)1 Bu)4 in the presence of excess l-(4-dimethylaminophenyl) ethanol is also an effective catalyst for the Meerwein-Ponndorf-Verley-type reduction.1 1 Similarly, Zr(0R)4 catalyze Oppenauer-type oxidation from benzylic alcohols to aldehydes or ketones in the presence of hydroperoxide.172,173... 

The Meerwein-Ponndorf-Verley (MPV) reduction is generally mediated by aluminum triiso-propoxide, Al(01Pr)3. In MPV reduction, reversible hydride transfer occurs via a six-membered transition state (Scheme 67). By removing acetone from the reaction system, the reversible reaction proceeds smoothly. The advantages of the reduction are the mildness of the reaction conditions, chemoselectivity, safety, operational simplicity, and its applicability to large-scale synthesis. It is reported that the addition of trifluoroacetic acid, significantly accelerates the reduction (Scheme 68) 304,305 in which case a catalytic amount of Al(0 Pr)3 is enough to complete the reaction. 

We recently reported a modified Meerwein-Ponndorf-Verley reduction in which low-boiling alcohols such as EtOH and w-PrOH, but preferably i-PrOH, were used at temperatures near 225 °C in the absence of aluminum alkoxides [42]. The carbonyl moiety of an olefinic aldehyde such as cinnamaldehyde was reduced selectively to the alcohol without the carbon-carbon double bond being affected (Scheme 2.7). Since base was not present, aldol and Claisen-Schmidt condensations were avoided. 

Transfer Hydrogenation Including the Meerwein-Ponndorf-Verley Reduction... 

More recently, Lnm alkoxides were shown to have much higher catalytic activity in this reaction, which allowed their use in only catalytic amounts [6, 7]. Later, however, much higher reactivities for Alln-catalyzed Meerwein-Ponndorf-Verley and Oppenauer (MPVO) reactions have also been achieved with dinuc-lear Alnl complexes [8,9] and with Alln alkoxides generated in situ [10]. Several reviews on the MPVO reactions have been published [11-14],... 

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