[19513-05-4] · C14H21Mn3O15 · Oxo(trimanganese) Heptaacetate · (MW 594.17)
(selective oxidizing agent; mediates addition of carboxylic acids to alkenes; reagent for allylic acetoxylation)
Alternate Name: manganese triacetate.
Solubility: insol most organic solvents; sol hot acetic acid; hydrolyzed by water.
Form Supplied in: brown or gray powder and chunks; widely available.
Purification: not usually necessary.
Handling, Storage, and Precautions: hygroscopic; avoid heat, sparks, and open flames.
In the presence of manganese triacetate, simple alkenes react with carboxylic acids (often solvent Acetic Acid) to give g-lactones (eqs 1 and 2)3,4 in a reaction which is thought to involve radical intermediates. This reaction can be performed on dienes5 and on alkenes which possess other potentially reactive groups such as alkynes6 (eq 3).7 A range of other carboxylic acids has been used in place of acetic acid.8,9
In addition to simple carboxylic acids, a variety of b-keto acids also undergo reaction with alkenes to give lactones (eq 4),9 and the intramolecular version of this reaction can be used effectively to produce polycyclic lactones (eq 5).10 This latter reaction has been adapted to the total synthesis of polycyclic natural products.
The formation of C-C bonds using MnIII salts is not restricted to the reaction of alkenes and carboxylic acids. A range of b-dicarbonyl compounds will also undergo additions to give dihydrofurans (eq 6)11 and other types of products. In particular, the intramolecular cyclization can be used to construct a variety of cyclic systems, using both monocyclizations (eq 7)12 and tandem cyclizations (eq 8).13 A sulfoxide group can take the place of one of the carbonyl groups, and in this case the chirality of the sulfoxide controls the absolute configuration of the product. In effect, the sulfoxide group has been used as a chiral auxiliary in this cyclization (eq 9).14
Enol ethers and enol esters can also serve as the alkene component of this type of reaction, the products being useful as precursors for furans and 1,4-dicarbonyl compounds (eqs 10 and 11).15,16 It is also possible to use simple ketones as the carbonyl component, although the yields are relatively low, and if the ketone is unsymmetrical, mixtures of products are obtained.17
Acetoxylation adjacent to both C=C and C=O double bonds is possible using manganese triacetate.18,19 Although the reaction tends to be substrate dependent and the yields variable (eq 12),19 it has been used to good effect in the synthesis of relatively complex polyfunctional systems that contain groups which might interfere (eqs 13 and 14).20,21
Manganese triacetate is reported to be superior to Ruthenium(VIII) Oxide and Cerium(IV) Ammonium Nitrate for the oxidation of N-protected indolines to indoles (eq 15).22 On treatment with manganese triacetate, aryldialkylamines undergo dealkylation, in which one alkyl group is replaced by an acetyl group,23 and in combination with Diphenyl Disulfide alkenes undergo regioselective addition of PhS and OH.24 Manganese triacetate was found to be the reagent of choice for the final step in a total synthesis of cyanocycline, which required the oxidation of the p-methoxyphenol to the corresponding quinone (eq 16).25
University of Salford, UK