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Synthesis 2004(1): 111-115  
DOI: 10.1055/s-2003-44362
PAPER
© Georg Thieme Verlag Stuttgart · New York

Copper(II) Tetrafluoroborate-Catalyzed Acetylation of Phenols, Thiols, Alcohols­, and Amines

Asit K. Chakraborti*, Rajesh Gulhane, Shivani
National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar, Punjab - 160062, India
Fax: +91(172)2214692; e-Mail: akchakraborti@niper.ac.in;
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Received 27 August 2003
Publikationsdatum:
09. Dezember 2003 (online)

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Abstract

Copper(II) tetrafluoroborate efficiently catalyzes acetyl­ation of structurally diverse phenols, alcohols, thiols, and amines with stoichiometric amounts of Ac2O under solvent-free conditions at room temperature. Acid-sensitive alcohols are smoothly acetylated without competitive side reactions. The reaction is influenced by the steric and electronic factors associated with the substrate as well as the anhydride. Acetylation of a sterically hindered substrate requires excess of anhydride and longer time. Acylation with less electrophilic anhydrides affords poor to moderate yields.

Key words

acetylation - copper(II) tetrafluoroborate - solvent-free

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Aldrich (India) 2003-2004 price (US $): Cu(BF4)2·xH2O (250 g, 107.80), In(OTf)3 (50 g, 417.00), Cu(OTf)2 (50 g, 416.00), Sc(OTf)3 (50 g, 1755.00), Sc(NTf2)3 (50 g, 3000.00), Ce(OTf)3 (? g, 421.50), LiOTf (100 g, 146.20). Estimated price (not being commercially available) (US $): Bi(OTf)3·xH2O (50 g, >315.95).

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Requirement of Ac2O(equiv): Sc(OTf)3 (1.5-as solvent), Sc(NTf2)3 (1.5), clays (2.0), zeolite (2.0), TMSOTf (1.5-as solvent), Cu(OTf)2 (2.0), Bi(OTf)3 (1.5-10), LiClO4 (2-10), Ce(OTf)3 (1.5), and LiOTf (5-8). Cu(BF4)2·xH2O(1).

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Requirement of high temperatures: Ytria-zirconia (80 °C), clays (40-80 °C), zeolite (60 °C), and LiClO4 (r.t.-40 °C). Low temperature required for acid-sensitive substrates: Cu(OTf)2 (-25 to 0 °C), Sc(OTf)3 (-50 to -20 °C), and TMSOTf (-10 °C). Cu(BF4)2·xH2O (r.t.).

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Requirement of longer times: Sc(OTf)3 (0.5-5 h), Sc(NTf2)3 (1 h), clays (2.5 h), zeolite (1.5-12 h), Cu(OTf)2 (1-2 h), Bi(OTf)3 (1-8.5 h), ytria-zirconia (2-15 h), LiClO4 (4-48 h), Ce(OTf)3 (0.2-24 h), and LiOTf (11-30 h). Cu(BF4)2·xH2O (0.25-1 h).

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Requirement of solvents: Sc(OTf)3 (MeCN or Ac2O); Sc(NTf2)3 (MeCN); clays (CH2Cl2 or CHCl3); ytria-zirconia (MeCN); TMSOTf (CH2Cl2, MeCN-EtOAc, Ac2O); Cu(OTf)2 (MeCN), Bi(OTf)3 (MeCN, THF, toluene, CH2Cl2), and Ce(OTf)3 (MeCN). Cu(BF4)2·xH2O (under neat conditions).