Synlett 2003(12): 1805-1808  
DOI: 10.1055/s-2003-41442
LETTER
© Georg Thieme Verlag Stuttgart · New York

Bismuth Oxide Perchlorate as a Highly Efficient Catalyst for Heteroatom Acylation Under Solvent-Free Conditions

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)214692; e-Mail: akchakraborti@niper.ac.in;
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Publikationsverlauf

Received 16 July 2003
Publikationsdatum:
28. August 2003 (online)

Abstract

Bismuth oxide perchlorate efficiently catalyzes the acetylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Sterically hindered and electron deficient phenols are acetylated in excellent yields with stoich­iometric amounts of Ac2O at room temperature. Acylation of acid-sensitive alcohols is carried out efficiently without competitive side reactions. Optically active substrates are acetylated without any detrimental effect on the optical purity.

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Typical procedure for acetylation: 2-Hydroxynaphthalene (360 mg, 2.5 mmol) was treated with Ac2O (0.24 mL, 2.5 mmol) under neat conditions at r.t. for 30 min (monitored by GCMS) under magnetic stirring in the presence of BiOClO4·xH2O (8.11 mg, 0.025 mmol, 1 mol%). The reaction mixture was diluted with Et2O (50 mL) and filtered through a cotton plug to separate the catalyst. The filtrate was washed successively with 2% aq NaOH (15 mL), brine (15 mL), dried (NaSO4) and concentrated to afford the product (442 mg, 95%), which was in full agreement with the spectral data (mp, IR, 1H NMR and EIMS) of an authentic sample of 2-acetoxynaphthalene. In most of the cases the products gave satisfactorily spectral (IR, 1H NMR and MS) data without any further purification. Wherever applicable, purification was done through crystallization (for solid) or passing through a column of silica gel (for liquid) and eluting with 5% Et2O in hexane.