Copper(II) Acetylacetonate: An Inexpensive Multifunctional Catalyst

Biographical Sketches

Antonio Carlos B. Burtoloso was born in Petrópolis (RJ), Brazil in 1976. He completed his B.Sc. in 2001 and his M.Sc. in 2002 at the Federal University of Rio de Janeiro. In 2002, he moved to Campinas (SP)-Brazil, where he is currently working for his Ph.D. under the supervision of Prof. Carlos Roque D. Correia at the State University of Campinas. His Ph.D. work is based on the investigation of new methodologies for the stereoselective synthesis of azetidines and azetidine alkaloids.

Introduction

Copper(II) acetylacetonate [Cu(acac)₂] (Figure 1) is a ­soluble copper catalyst that has been widely employed in many types of reactions. It can be readily and easily prepared [1] from the reaction of acetylacetone with ­copper(II) sulfate in aqueous basic solution, and is ­isolated as a blue solid.

Figure 1 Copper(II) acetylacetonate

Although Cu(acac)₂ has been mostly used as catalyst in different reactions involving diazocompounds, [2] it is also described as a catalyst for other types of reactions such as benzylation of alcohols, [3] reduction of aromatic nitro ­compounds, [4] aziridination, [5] [6] and epoxidation. [6] The easy access and low cost of copper(II) acetylacetonate, to­gether with its varied applications as catalyst, make Cu(acac)₂ a powerful reagent in organic synthesis.

Abstract

(A) Benzylation of Alcohols: Sirkecioglu and co-workers [3] have found that selective O-benzylation of primary hydroxy compounds can be performed in the presence of catalytic amounts of Cu(acac)2 and benzyl chloride in good to high yields.
(B) X-H Insertion Reactions: Cu(acac)2 can catalyze many X-H (X = N, O, S, P, Se) insertion reactions. This scheme illustrates a recent example of an intra­molecular N-H insertion reaction from diazoketones for the construction of fully substituted azetidines by Correia and Burtoloso. [7]
(C) Reduction of Aromatic Nitro Compounds: Hanaya and co-workers [4] reported a protocol for the reduction of aromatic nitro compounds to amines in high yields and in short ­reaction times in the presence of NaBH4 and Cu(acac)2 as catalyst.
(D) Cyclopropanation: Cu(acac)2 catalyzes both intermolecular [8] and intramolecular [9] ­cyclopropanation of double bonds with diazo compounds.
(E) Aziridination of Olefins: Kantam and co-workers [5] have reported a novel recyclable catalytic system for aziridination of olefins using PhI=NTs in the presence of Cu(acac)2 immobilized in ionic liquids. This methodology ­furnishes aziridines in good yields and with fast reaction rates.
(F) Reduction of α-Diazo Carbonyl Compounds: Diazo carbonyl compounds are reduced in the presence of Cu(acac)2 and Bu3SnH. [10]
(G) Synthesis of Conjugated Enynes from Alkenyldialkylboranes: The cross-coupling reaction of (E)- and (Z)-1-alkenyldialkyl­boranes with (trimethylsilyl)ethynyl bromide in the presence of Cu(acac)2 furnishes conjugated enynes under very mild conditions. [11]

References

• Preparation of Cu(acac)₂: Copper(II) acetylacetonate was prepared by reaction of CuSO₄ with equimolar quantities of acetylacetone and NaOH in aqueous solution. After the subsequent addition of acetylacetone (1 equiv) and CuSO₄·H₂O (0.5 equiv) in basic solution with stirring, a blue precipitate was obtained. The precipitate was filtered, dried in vacuum and recrystallized from glacial AcOH to give blue needles:
• 1a Graddon DP. J. Inorg. Nucl. Chem.  1960,  14:  161 
• 1b For another experimental procedure, see: Peacock RD. J. Chem. Educ.   1971.  48:  p.133 
• 2For many applications of Cu(acac)₂ in reactions with diazo compounds, see:
• 2 Doyle MP. McKervey MA. Ye T. Modern Catalytic Methods for Organic Synthesis with Diazo Compounds From Cyclopropanes to Ylides   Wiley; New York: 1998. 
• 3 Sirkecioglu O. Karliga B. Talinli N. Tetrahedron Lett.  2003,  44:  8483 
• 4 Hanaya K. Muramatsu T. Kudo H. J. Chem. Soc., Perkin Trans. 1  1979,  2409 
• 5 Kantam ML. Kavita VNB. Haritha Y. Synlett  2004,  525 
• 6 Aggarwal VK. Synlett  1998,  329 
• 7 Burtoloso ACB. Correia CRD. Tetrahedron Lett.  2004,  45:  3355 
• 8 Solomon RG. Kochi JK. J. Am. Chem. Soc.  1973,  95:  3300 
• 9 Hudlicky T. Kutchan TM. Wilson SR. Mao DT. J. Am. Chem. Soc.  1980,  102:  6353 
• 10 Tan Z. Qu Z. Chen B. Wang J. Tetrahedron  2000,  56:  7457 
• 11 Hoshi M. Shirakawa K. Synlett  2002,  1101