Aluminum t-Butoxide1


[556-91-2]  · C9H27AlO3  · Aluminum t-Butoxide  · (MW 246.32)

(metal alkoxide used in Meerwein-Ponndorf-Verley reduction of ketones2 and Oppenauer oxidation of alcohols3)

Physical Data: white powder; mp >300 °C (sealed tube); dimeric structure in benzene; can be recryst from benzene; sublimes at 180 °C.

Solubility: v sol organic solvents, especially alcohols, benzene, toluene, and xylene.

Preparative Method: prepared by reacting Aluminum shavings with dry t-butyl alcohol using a catalytic amount of Mercury(II) Chloride.1c,1e

Handling, Storage, and Precautions: use in fume hood. Air and moisture sensitive; extremely destructive to tissue of the mucous membranes and upper respiratory tract, eyes, and skin and should be handled with appropriate caution. Contact via inhalation route is particularly hazardous.

Meerwein-Ponndorf-Verley Reduction.

The reagent has been used for the reduction of 3-keto steroids, affording predominantly the axial alcohol. Thus reduction of the monoethylene ketal of 3,20-pregnanedione with the reagent in s-butyl alcohol, followed by transketalization, gave 3b-hydroxy-5b-pregnan-20-one in modest excess over the 3a-epimer.2 Separation and oxidation of the undesired epimer followed by reduction as above gave, after several cycles, high conversion of the dione to the desired 3b-alcohol (eq 1)

Oppenauer Oxidation.

Aluminum t-butoxide is frequently the reagent of choice for this mild oxidation of secondary alcohols to ketones. Since most other oxidizable groups remain unaffected, the method has found wide use in the steroid field, as illustrated by the oxidation of cholesterol to cholest-4-en-3-one (eq 2).3 The accompanying double bond migration commonly occurs during reactions of steroids of this type.

Aldol Condensation.

The reagent has also found limited use as a base for the aldol condensation of methyl ketones, as illustrated by the preparation of dypnone from acetophenone (eq 3).4

Amine Alkylation.

In the presence of catalytic amounts of Raney Nickel W-2 and aluminum t-butoxide, primary and secondary amines are alkylated by alcohols (eqs 4 and 5).5

1. (a) Wilds, A. L. OR 1944, 2, 221. (b) Djerassi, C. OR 1951, 6, 207. (c) Furniss, B. S.; Hanniford, A. J.; Smith, P. W. G.; Tatchell, A. R. Vogel's Handbook of Practical Organic Chemistry, 5th ed.; Longman: Harlow, 1989; pp. 608-611. (d) Coffey, S.; Boyd, V. JCS 1954, 2468. (e) Wayne, W.; Adkins, H. OSC 1955, 3, 48.
2. (a) Bach, G.; Capitaine, J.; Engel, C. R. CJC 1968, 46, 733. (b) Bouchard, R.; Engel, C. R. CJC 1968, 46, 2201.
3. Oppenauer, R. V. OSC 1955, 3, 207.
4. Wayne, W.; Adkins, H. OSC 1955, 3, 367.
5. Botta, M.; De Angelis, F.; Nicoletti, R. S 1977, 722.

Gary W. Morrow

The University of Dayton, OH, USA

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