Meerwein- Pondorf-Verley reduction

The reaction which is carried out in presence of isopropyl alcohol is also called Meerwein-Pondorf-Verley reduction. An example is the reduction of crotonaldehyde to crotyl alcohol. 

Aluminium Alkoxides and Ketones Meerwein-Pondorf-Verley Reduction... 

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. 

Aluminum methoxide Al(OMe)3 is a solid which sublimes at 240 °C in vacuum. Aluminum isopropoxide melts in the range 120-140 °C to a viscous liquid which readily supercools. When first prepared, spectroscopic and X-ray evidence indicates a trimeric structure which slowly transforms to a tetramer in which the central Al is octahedrally coordinated and the three peripheral units are tetrahedral.162,153 Intramolecular exchange of terminal and bridging groups, which is rapid in the trimeric form, becomes very slow in the tetramer. There is MS and other evidence that the tetramer maintains its identity in the vapour phase.164 Al[OCH(CF3)2]3 is more volatile than Al[OCH(Me)2]3 and the vapour consists of monomers.165 Aluminum alkoxides, particularly Al(OPr )3, have useful catalytic applications in the synthetic chemistry of aldehydes, ketones and acetals, e.g. in the Tishchenko reaction of aldehydes, in Meerwein-Pondorf-Verley reduction and in Oppenauer oxidation. The mechanism is believed to involve hydride transfer between RjHCO ligands and coordinated R2C=0— A1 groups on the same Al atom.1... 

Figure 46. Catalyst preparation for an asymmetric Meerwein-Pondorf-Verley reduction.

Equation 15.3.1 Meerwein-Pondorf-Verley reduction of 4-tert-butylcyclohexanone 27... 

Fig. 15.6 Meerwein-Pondorf-Verley reduction of 4-tert-bytylcyclohexanone 27 catalyzed by alkali-metal exchanged BEA effect of cation on cw-4-tert-bytylcyclohexanol selectivity...

The Oppenauer oxidation can also afford a convenient alternative to more traditionally used oxidants. Oxidation of quinine (13) using benzophenone and KO/Bu gave the ketone in excellent yield (Figure 3.14) other oxidants were less effective [27]. This reaction can be viewed as an Oppenauer oxidation or a Meerwein-Pondorf-Verley reduction, depending on whether one considers the oxidation or the reduction to be the primary reaction. A magnesium-catalyzed Meerwein-Pondorf-Verley reduction was determined to form significant amounts of impurities in a Grignard reaction [28]. 

A pivalamide of an indole, introduced with PvCl (NaH, DMF, 0°C, 1 h, 96% yield) is efficiently cleaved with MeSNa (MeOH, 20°C, 2h, 96% yield).The use EDA (THE, 45°C, 79-93% yield) cleaves the pivalamide by a Meerwein-Pondorf-Verley reduction. 

Campbell, E. J. Zhou, H. and Nguyen, S. B. T., Catalytic Meerwein-Pondorf-Verley reduction by simple aluminum complexes. Org. Lett., 3 15,2391-2393,2001. 

Cyclopentanol. Cyclopentyl alcohol hydroxy cyclopentane. C5HioO mol wt 86.13. C 69.72%, H 11.70%, O 1158%. Prepd by modified Meerwein-Pondorf-Verley reduction of cyclopentanone in the presence of aluminum hoprnpoxide and sodium hydroxide Truett, Moulton, J... 

Meerwein-Pondorf-Verley reduction is the hydrogenation in which alcohols are used as a source of hydrogen, and one of the hydrogen transfer reactions. M-P-V reduction of aldehydes, ketones and esters are efficiently catalyzed by hydrous Zr02 catalyst[18]. In these reactions, 2-propanol is the best for hydrogen source. 

The intermediate formed in the aluminum isopropoxide (AI[OCH(CH3)2]s) (Meerwein-Pondorf-Verley) reduction of aldehydes and ketones. Hydrolysis produces the corresponding alcohol. See this Chapter (Reduction). 

As is apparent (Table 26.33), the reduction of methylcyclohexanones (entries 1, 2, 4, 6, and 7) requires longer reaction times to achieve satisfactory conversions. This results in the equilibration of epimeric alcohols, leading to higher formation of more stable alcohols (entries 6 and 7). The isomerization is because of the intermolecular hydride transfer, which is similar to Meerwein-Pondorf-Verley reduction of ketones with aluminum alkoxides (Scheme 26.8). 

Transfer hydrogenation of ketones has its origin in Meerwein—Pondorf-Verley reduction which appeared in the mid-1920s, where the use of stoichometiic aluminium isopropoxide allowed for hydrogen transfer from propan-2-ol to a ketone [17-19], and was later introduced in its asymmetric version by Doering and Young... 

M = main group metal, e.g. Al Fig. 1 Meerwein—Pondorf—Verley reduction of ketones... 

The use of alumina-supported materials has been reviewed (Posner, 1978). Alumina has been used to support various noble metals and the products used to hydrogenate alkenes (Sermon et al., 1974 Schwartz and Bathija, 1976). Cannizzaro and Meerwein-Pondorf-Verley reductions have been reported using either alumina or alumina impregnated with 2-propanol (Lamb et al., 1974 Posner, 1978 cf., Posner e/ al., 1977). 

A streamlined route from 87 to 94 was also developed. Thus, Meerwein-Pondorf-Verley reduction of 87 provided diol 95. Treatment of 95 with bromine in methanol gave )3-bromolactone 97, presumably via intermediate bromonium ion 96. Reaction of 97 with sodium methoxide gave 94. Note that this route takes advantage of the same stereochemical principles followed by the epoxide route to 94. 

Dilger, A.K., Gopalsamuthiram, V., and Burke, S.D. (2007) A two-directional approach to a (-)-dictyostatin C11-C23 segment development of a highly diastereoselective, Idnetically-controlled Meerwein-Pondorf-Verley reduction. J. Am. Chem. Soc., 129, 16273-16277. 

---