Manganese(III) acetate

Introduction

Metal-mediated oxidative radical cyclisations have become a very important method in synthetic chemistry over the last 40 years. [1] Of particular importance is the use of Mn(OAc)₃ which acts as a one-electron oxidant. In 1968, it was shown to oxidise acetic acid leading to γ-lactones in the presence of alkenes. [2] [3] The mechanism of these reactions is not fully understood but is thought to proceed as shown in Scheme 1. Since then, a variety of alternative substrates to acetic acid, especially enolisable 1,3-dicarbonyls, have been successfully employed in related reactions, particularly cyclisations, to form 5- and 6-membered rings. [4] The solvent of choice is acetic acid; other solvents (EtOH, CH₃CN, DMSO) tend to give lower yields. [4]

As Mn(OAc)₃ is troublesome to prepare and highly deliquescent, the dihydrate form of the complex [Mn(OAc)₃·2H₂O] is generally used and this is commercially available. [5] [6]

Scheme 1

References

• 1 Iqbal J. Bhatia B. Nayyar NK. Chem. Rev.  1994,  94:  519 
• 2 Heiba EI. Dessau RM. Koehl WJ. J. Am. Chem. Soc.  1968,  90:  5905 
• 3 Bush JB. Finkbeiner HJ. J. Am. Chem. Soc.  1968,  90:  5903 
• 4a Snider BB. Chem. Rev.  1996,  96:  339 
• 4b Melikyan GG. Aldrichimica Acta  1998,  31:  50 
• 5 Midgley G. Thomas CB. J. Chem. Soc., Perkin Trans. 2  1984,  1537 
• 7 Bar G. Parsons AF. Thomas CB. Tetrahedron  2001,  57:  4719 
• 8 Garzino F. Méou A. Brun P. Tetrahedron Lett.  2000,  41:  9803 
• 9 Atteni B. Cerreti A. D’Annibale A. Resta S. Trogolo C. Tetrahedron  1998,  54:  12029 
• 10 Zoretic PA. Weng X. Caspar ML. Davis DG. Tetrahedron Lett.  1991,  32:  4819 
• 11 Linker U. Kersten B. Linker T. Tetrahedron  1995,  51:  9917 
• 12 Coleman JP. Hallcher RC. Mackins DE. Rogers TE. Wagenknecht JM. Tetrahedron  1991,  47:  809 
• 13 Iwasawa N. Funahashi M. Hayakawa S. Narasaka K. Chem. Lett.  1993,  545 
• 14 Nishino H. Bull. Chem. Soc. Jpn.  1985,  58:  1922 

6

Mn(OAc)₂·4H₂O and Mn(OAc)₃·2H₂O are commercially available.