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

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.

Keywords

acylations - bismuth compounds - catalysis - solvent-free reactions - heteroatoms

References

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27

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.