Manganese(III) Acetate1

Mn(OAc)3
(Mn(OAc)3)

[993-02-2]  · C6H9MnO6  · Manganese(III) Acetate  · (MW 232.09) (Mn(OAc)3.2H2O)

[19513-05-4]  · C6H13MnO8  · Manganese(III) Acetate  · (MW 268.13)

(one-electron oxidant used to oxidize acetic acid and b-dicarbonyl compounds to the corresponding radical and for a-acetoxylation of enones)

Physical Data: the commercially available dihydrate is cinnamon brown. The anhydrous form is dark brown. The crystal structure of the anhydrous form indicates an oxo-centered trimer with bridging acetates.2

Solubility: sol acetic acid, ethanol, and a variety of other organic solvents; disproportionates in water.

Preparative Methods: commercially available dihydrate is easily prepared by the reaction of manganese(II) acetate with potassium permanganate in acetic acid at reflux.1 The anhydrous form is prepared in acetic acid and acetic anhydride.1

Mn(OAc)3 has been extensively used for the oxidative addition of acetic acid to alkenes to give g-butyrolactones.3,4 The addition of acetic acid to alkenes in acetic acid at reflux is quite general.1 Acetic Anhydride and sodium acetate are often used as additives that modify the rate of reaction and ratio of products. With simple carboxylic acids, this reaction is limited to acetic acid and other acids which can be used as solvent. Mechanistic studies5a have shown that the rate determining step is formation of a MnIII enolate which rapidly transfers an electron to give the carboxymethyl radical and MnII. This radical adds to the alkene to give a g-carboxyalkyl radical that is oxidized by a second equivalent of Mn(OAc)3 to give mixtures of lactone, alkene, and g-acetoxycarboxylic acid (eq 1), depending on the exact reaction conditions and structure of the alkene.6

The lactonization reaction is much more facile with cyanoacetic acid and malonic acid, which undergo the rate-determining enolization more rapidly in acetic acid at rt (eq 2).1,5,7 Malonic acid gives only bis-lactone 2:1 adducts resulting from the addition to two molecules of alkene (eq 3).8

Mn(OAc)3 oxidizes ketones and aldehydes to a-carbonyl radicals which add to alkenes to give g-oxo radicals. If these radicals are secondary, they are not oxidized unless Copper(II) Acetate is used as a co-oxidant (eqs 4 and 5).9,10 Instead they undergo chain-transfer reactions to give saturated carbonyl compounds. Tertiary radicals give mixtures of saturated and unsaturated carbonyl compounds.

These reactions proceed in good yield based on oxidant consumed but must be carried out with a large excess of ketone or aldehyde, which is sometimes used as the solvent, since the products are oxidized further to give radicals at about the same rate as the starting carbonyl compound is oxidized.

A wide variety of b-dicarbonyl compounds can be oxidized by Mn(OAc)3 to radicals in the presence of alkenes.11 Addition of the radical to styrene and other electron-rich alkenes affords dihydrofurans. Addition to enol ethers occurs readily to give 1-alkoxy-1,2-dihydrofurans, which can be hydrolyzed to yield 1,4-diketones or dehydrated to form furans.12

Intramolecular versions of these reactions provide an efficient route to cyclic ring systems. Oxidation of unsaturated b-keto acids affords cyclopentanones fused to g-lactones (eq 6).13

Oxidation of unsaturated b-keto esters affords a-keto radicals which add to alkenes to give alkyl radicals which are oxidized to alkenes in the presence of Cu(OAc)2 (see Manganese(III) Acetate-Copper(II) Acetate). If the alkyl radical is a 4-phenylbutyl radical, cyclization onto the aromatic ring results in the formation of a tetralin. This reaction occurs stereospecifically, as shown in the synthesis of O-methylpodocarpic acid (eq 7).14

Haloalkenes are compatible with radical generation by oxidation of b-dicarbonyl compounds with Mn(OAc)3 and can be used to control the regiochemistry of the cyclization (eq 8).15 Loss of HCl from the intermediate affords the naphthol in 79% yield in one pot. This reaction is compatible with allylic oxygen functionality and has been used for the synthesis of okicenone (eq 9).16

Oxidation of allylic b-keto amides with Mn(OAc)3 in EtOH affords g-lactams. The primary radical formed in the cyclization abstracts a hydrogen from the solvent (eq 10).17 Similarly, saturated g-lactones can be prepared by oxidation of allylic malonates and acetoacetates.18

The radicals formed by oxidation of 1,3-dicarbonyl compounds will add to electron-rich naphthalenes (eq 11).19 Tetralins and dihydronaphthalenes can be formed by oxidation of diethyl a-benzylmalonate in the presence of an alkene or alkyne (eq 12).20-22

a-Acetoxylation of conjugated enones with Mn(OAc)3 in acetic acid proceeds in modest yield.23 The reaction proceeds in much better yield with well-dried oxidant in refluxing benzene (eq 13).24 A wide variety of a-esters can be introduced by exchange of carboxylic acids with Mn(OAc)3 in benzene at reflux prior to the addition of the enone.25 This procedure is applicable to a- and b-alkoxy enones26 and is suitable for a-acetoxylation of aryl alkyl ketones.27


1. (a) de Klein, W. J. In Organic Syntheses by Oxidation with Metal Compounds; Mijs, W. J.; de Jonge, C. R. H. I., Eds.; Plenum: New York, 1986; Chapter 4. (b) Badanyan, Sh. O.; Melikyan, G. G.; Mkrtchyan, D. A. RCR 1989, 58, 286. (c) Snider, B. B. Chemtracts-Org. Chem. 1991, 4, 403. (d) Demir, A. S.; Jeganathan, A. S 1992, 235. (e) Melikyan, G. G. S 1993, 833.
2. Hessel, L. W.; Romers, C. RTC 1969, 88, 545.
3. Bush, J. B., Jr.; Finkbeiner, H. JACS 1968, 90, 5903.
4. Heiba, E. I.; Dessau, R. M.; Koehl, W. J., Jr. JACS 1968, 90, 5905.
5. (a) Fristad, W. E.; Peterson, J. R.; Ernst, A. B. T 1986, 42, 3429. (b) Snider, B. B.; Patricia, J. J.; Kates, S. A. JOC 1988, 53, 2137.
6. Okano, M. BCJ 1976, 49, 1041.
7. Corey, E. J.; Gross, A. W. TL 1985, 26, 4291.
8. (a) Fristad, W. E.; Hershberger, S. S. JOC 1985, 50, 3143. (b) Ito, N.; Nishino, H. Kurosawa, K. BCJ 1983, 56, 3527.
9. Nikishin, G. I.; Vinogradov, M. G.; Verenchikov, S. P.; Kosyukov, I. N.; Kereselidze, R. V. ZOR 1972, 8, 539.
10. Vinogradov, M. G.; Verenchikov, S. P.; Nikishin, G. I. ZOR 1972, 8, 2467.
11. Heiba, E. I.; Dessau, R. M. JOC 1974, 39, 3456.
12. (a) Corey, E. J.; Ghosh, A. K. CL 1987, 223. (b) Corey, E. J.; Ghosh, A. K. TL 1987, 28, 175.
13. Corey, E. J.; Kang, M. JACS 1984, 106, 5384.
14. Snider, B. B.; Mohan, R.; Kates, S. A. JOC 1985, 50, 3659.
15. Snider, B. B.; Zhang, Q.; Dombroski, M. A. JOC 1992, 57, 4195.
16. Snider, B. B.; Zhang, Q. JOC 1993, 58, 3185.
17. (a) Cossy, J.; Leblanc, C. TL 1989, 30, 4531. (b) Cossy, J.; Bouzide, A.; Leblanc, C. SL 1993, 202.
18. Bertrand, M. P.; Surzur, J. M.; Oumar-Mahamat, H.; Moustrou, C. JOC 1991, 56, 3089.
19. (a) Citterio A.; Santi, R.; Fiorani, T.; Strologo, S. JOC 1989, 54, 2703. (b) Citterio, A.; Fancelli, D.; Finzi, C.; Pesce, L.; Santi, R. JOC 1989, 54, 2713.
20. Snider, B. B.; Buckman, B. O. T 1989, 45, 6969.
21. Citterio, A.; Sebastiano, R.; Marion, A.; Santi, R. JOC 1991, 56, 5328.
22. Santi, R.; Bergamini, F.; Citterio, A.; Sebastiano, R.; Nicolini, M. JOC 1992, 57, 4250.
23. Williams, G. J.; Hunter, N. R. CJC 1976, 54, 3830.
24. (a) Dunlop, N. K.; Sabol, M. R.; Watt, D. S. TL 1984, 25, 5839. (b) Jeganathan, A.; Richardson, S. K.; Watt, D. S. SC 1989, 19, 1091. (c) Gross, R. S.; Kawada, K.; Kim, M.; Watt, D. S. SC 1990, 19, 1127.
25. (a) Demir, A. S.; Jeganathan, A.; Watt, D. S. JOC 1989, 54, 4020. (b) Demir, A. S.; Akgün, H.; Tanyeli, C.; Sayrac, T.; Watt, D. S. S 1991, 719.
26. (a) Demir, A. S.; Sayrac, T.; Watt, D. S. S 1990, 1119. (b) Demir, A. S.; Saatcioglu, A. SC 1993, 23, 571.
27. Demir, A. S.; Camkerten, N.; Akgun, H.; Tanyeli, C.; Mahasneh, A. S.; Watt, D. S. SC 1990, 20, 2279.

Barry B. Snider

Brandeis University, Waltham, MA, USA



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