Ponndorf

Benzhydrol (Diphenylcarbinol), (C HJ,CH OH, from Bettzo-phenone. The Meerwem-Ponndorf-Verley Reductions. 

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. 

Secondary alcohols may be oxidised to the corresponding ketones with aluminium ferf.-butoxlde (or tsopropoxlde) In the presence of a large excess of acetone. This reaction Is known as the Oppenauer oxidation and Is the reverse of the Meerweln - Ponndorf - Verley reduction (previous Section) it may bo expressed ... 

Meerwein-Ponndorf-Veriey Reduction opposite of Oppenauer oxidation Synthesis 1994, 1007 Organic Reactions 1944, 2, 178... 

Reduction of iminium salts with diborane and by the Meerwein-Ponndorf method have been reported (89). 

In boiling ethanol, under nitrogen and in the presence of palladized charcoal, 2-acetyl-l,4-dihydro-3-methylquinoxaline (30) undergoes dismutation to give a mixture of 2-acetyl-3-methylquinoxaline, 2-acetyl-l,2,3,4-tetrahydro-3-methylquinoxaline (33), and 2-l -hydroxy-ethyl-3-methylquinoxaline (34), The latter compound is the product of sodium borohydride or Meerwein-Ponndorf reduction of 2-acetyl-3-methylquinoxaline. 

The reduction of ketones to secondary alcohols and of aldehydes to primary alcohols using aluminum alkoxides is called the Meerw>ein-Ponndorf-Verley reduction. The reverse reaction also is of synthetic value, and is called the Oppenauer oxidation. ... 

The Meerwein-Ponndorf-Verley procedure has largely been replaced by reduction procedures that use lithium aluminum hydride, sodium borohydride or derivatives thereof.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... 

The reduction product arising either from the decomposition1 of r-BuMgBr into isobutene and HMgX or through a six-membered Meerwein Ponndorf-Vcrlcy-like mechanism is also obtained (about 20% yield). 

Bei Ausbildungeines neuen Chiralitatszentrums werden epimere Hydroxy-carbon-saureester gebildet, deren Verhaltnis von der Art des Losungsmittels abhangt13. Auch nach Meerwein-Ponndorf nicht-reduzierbare Oxo-carbonsaure-ester konnen mit Natriumboranat in Reaktion gebracht werden14. 

Stabile aquatoriale Alkohole aus behinderten Cycloalkanonen miissen also durch Meerwein-Ponndorf-Ver-ley-Reduktion Oder durch Epimerisierung des instabilen axialen Alkohols in einem Schritt mit Lithium-alanat/4 Aluminiumchlorid (S. 335 f.) hergestellt werden3. 

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... 

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