Magnesium Oxide

MgO

[1309-48-4]  · MgO  · Magnesium Oxide  · (MW 40.31)

(dehydrohalogenation;1 reductions;2,6-8 alkene synthesis;3 oxidations;9 epoxide opening;10 acylations12,13)

Physical Data: mp 2852 °C; bp 3600 °C; d 3.58 g cm-3.

Solubility: sol water (0.0086 g/100 mL at 30 °C).

Form Supplied in: white powder.

Preparative Method: dehydration of Mg(OH)2 at 1100 °C for 2 h.

Handling, Storage, and Precautions: tumorigenic (olfactory and respiratory system); avoid breathing dust; incompatible with strong oxidizing agents; air and moisture sensitive. May react violently on mixing with phosphorus pentachloride, chlorine trifluoride, or bromine pentafluoride.

Reactions with Aldehydes and Ketones.

a,b-Unsaturated ketones can be prepared from a-bromo ketones when treated with magnesium oxide in DMF (eq 1).1

In the presence of a hydrosilane, magnesium oxide catalyzes the conversion of carbonyl compounds to silyl alcohols (eq 2).2

Aldehydes are converted to alkenes in a biphasic solid-liquid system with magnesium oxide via Wittig-Knoevenagel or Wittig-Horner reactions (eq 3).3

Allylic silylcyanohydrins can be prepared in excellent yields upon treatment of an a,b-unsaturated ketone with Cyanotrimethylsilane and magnesium oxide. In most cases, less than 1% of the 1,4-adduct was detected (eq 4).4

Reaction with Alkynes.

Both 1 and 2-butyne can be isomerized at low temperature (<100 °C) to yield 1,3-butadiene.5

Reductions, Hydrogenolyses, and Dehydrogenation.

As a reduction catalyst, magnesium oxide aids in the dechlorination of dichloropyrimidines to yield pyrimidines.6 1,3-Butadiene is converted to cis-2-butene under similar conditions.7 In a unique modification of the Meerwein-Pondorf-Verley reduction, a,b-unsaturated ketones are converted to allylic alcohols in moderate yield (eq 5).8

Conversely, magnesium oxide serves as a dehydrogenation catalyst. Primary amines are converted to nitriles in good yield (eq 6).9

Miscellaneous.

Epoxides are opened regioselectively by cyanotrimethylsilane in the presence of magnesium oxide (eq 7).10

This reagent also serves as an efficient acid scavenger during the N-protection of a-amino acids with benzyloxycarbonyl chloride (Benzyl Chloroformate).11 In acylation reactions, magnesium oxide can be used to C-acylate malonates12 and N-acylate anilines.13


1. Kutney, J. P.; Cable, J.; Gladstone, W. A. F.; Hanssen, H. W.; Torupka, E. J.; Warnack, W. D. C. JACS 1968, 90, 5332.
2. Izumi, Y.; Nanami, H.; Higuchi, K.; Onaka, M. TL 1991, 32, 4741.
3. Moison, H.; Texier-Boullet, F.; Foucaud, A. T 1987, 43, 537.
4. Higuchi, K.; Onaka, M.; Izumi, Y. CC 1991, 1035.
5. Sato, K.; Hattori, H. CL 1982, 1881.
6. (a) Wittaker, N. JCS 1951, 1565. (b) Lythgoe, B.; Rayner, L. S. JCS 1951, 2323.
7. Hattori, H.; Tanaka, Y.; Tanabe, K. JACS 1976, 98, 4652.
8. Kaspar, J.; Trovarelli, A.; Lenardo, M.; Graziani, M. TL 1989, 30, 2705.
9. Xu, B.; Yamaguchi, T.; Tanabe, K. CL 1988, 281.
10. Sugita, K.; Ohta, A.; Onak, M.; Izumi, Y. CL 1990, 481.
11. du Vigneaud, V.; Miller, G. L. Biochem. Prep. 1952, 2, 79.
12. Skarzewski, J. TL 1989, 45, 4593.
13. Lazar, J.; Bernath, G. JHC 1990, 27, 1885.

Brian A. Roden

Abbott Laboratories, North Chicago, IL, USA



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