Mechanism of the Meerwein-Ponndorf-Verley Reduction¹

Abstract

yielded 1.40 g. (95%) of solid anít-7-norbornenol (IX), m.p. after vapor phase chromatographic purification, 117-118"; reported*• m.p. is 117-118". This material was hydrogenated to 7-norbomeol, identical with the 7-norbomeol obtained from VII and VIII above.Pyrolysis of the acetate (VII). Pyrolysis of the acetate (VII) was effected by injecting a sample into the sample inlet of a Beckman GC-2 heated at 225" with a column temperature of 130". No benzene could be detected among the many volatile products. The chief product, as shown by vapor phase chromatography, infrared and ultraviolet comparison with an authentic sample, was benzyl acetate.The acetate (VII) could also be pyrolyzed at 375°in a 9 in. column packed with glass helices to give good yields of benzyl acetate. With this apparatus the acetate (VII)was not pyrolyzed at 275®. Pyrolysis at a lower temperature in the gas chromatograph was probably promoted by carbonized materials known to be present in the inlet tube. Hydrolysis of 7-norbomadienyl acetate (VII). Hydrolysis of the acetate (VII) was attempted under the following conditions with uniformly negative results. In every instance the acetate was hydrolyzed but did not give the alcohol (VIII) . In most cases infrared analysis indicated ring opening.(1) IN hydrochloric acid/50% aqueous methanol at room temperature for 3 hr.(2) 2N hydrochloric acid/HiO at room temperature overnight.(3) IN potassium hydroxide/75% aqueous methanol overnight at room temperature under nitrogen.(4) IN sodium methoxide/methanol at room temperature for 2 hr. under nitrogen.Acid hydrolysis of the ether (VI) A solution of 0.5 g. (0.003 mole) of ether (VI) in 1 ml. of 50% sulfuric acid (0.018 mole) was allowed to stand at room temperature for 1 hr. Ice and water were added and the product was extracted with dichloromethane. None of the alcohol (VIII) could be detected in the product which appeared to consist chiefly of a saturated diol.

Transfer Hydrogenation Including the Meerwein‐Ponndorf‐Verley Reduction

“…The mechanism of the MPVO reactions has been investigated and questioned on several occasions, and a variety of direct hydrogen-transfer pathways have been suggested (see Scheme 20.4) [31][32][33][34][35]. Recently, racemization of D-labeled 1-phenylethanol with deuterated samarium(III) isopropoxide (17) proved that the MPVO reaction occurs via a direct hydrogen transfer from the a-position of the isopropoxide to the carbonyl carbon of the substrate (Scheme 20.7) [31].…”

Bimetallic isopropoxides M[Al(OC3Hi7)4]3 (M = Pr, Nd)—catalyzed reduction of 2-octanone and benzophenone

“…Hence a simple kinetic equation, k obs = d[1]/dt, was assumed for calculation of reaction rates. Similarly these rates were also calculated [25] by plotting oscillator strengths (P ) with time and are given correspondingly in parentheses in (3)) involves the reduction of the keto (>C=O) group to the corresponding secondary alcoholic (>CH-OH) group using aluminum isopropoxide as the catalyst [32,33]. After completion of the reaction, the reaction mixture is acidified with sulfuric acid and then the product is distilled off: The reaction proceeds through coordination of ketone and alcohol by forming a 6-membered cyclic transition state complex as shown in reaction (4) Hence the increase in the intensity of the bands with time is assigned to the formation of the intermediate complex 1, as given in reaction (4), which results in the formation of the final reduced product alcohol and oxidized product acetone.…”

Magnesium Meerwein−Ponndorf−Verley−Oppenauer Reaction. The Origin of an Impurity in PDA-641 Batches

“…The initial step involves complexation of the carbonyl group with the metal atom . The activated aldehyde then accepts the hydride from the magnesium alcoholate (Scheme ) 3 …”

“…Cf. refs , b. In fact, a slow, dropwise addition of MeMgCl into 4 in THF produced extensive frothing, and 4 was recovered upon quenching.…”