Tris(pentafluorophenyl)borane catalyzed acylation of alcohols, phenols, amines, and thiophenols under solvent-free condition Santosh Kumar Prajapti, Atulya Nagarsenkar, Bathini Nagendra Babu ⇑ Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, Balanagar, Hyderabad 500037, India article info Article history: Received 23 December 2013 Revised 23 January 2014 Accepted 25 January 2014 Available online 1 February 2014 Keywords: Acylation Lewis acid Tris(pentafluorophenyl)borane Nontoxic abstract The acylation of alcohols, phenols, amines, and thiophenols was accomplished with 0.5 mol % of tris (pentafluorophenyl)borane [B(C 6 F 5 ) 3 ] at ambient temperature under solvent-free condition. Major advantages of this method include high yield, short reaction time, simple procedure, compatibility with sensitive protecting groups as well as other functional groups, absence of racemization of optical active compounds, and epimerization of sugars. Ó 2014 Elsevier Ltd. All rights reserved. Acylation of alcohols, phenols, and amines are one of the most important manipulation in synthetic chemistry, which serve as imperative synthetic intermediate especially in the synthesis of polyfunctional molecules such as nucleoside, natural products, and carbohydrates. Acylation is a very frequently employed organic transformation in multistep organic synthesis because of the afflu- ence of accession as well as mild condition for de-protection. Usu- ally, anhydrides and acid chlorides are the most commonly used acyl source to achieve acylated product either in the presence of acid or base. The deprived nucleophilic properties of hydroxylic com- pounds, particularly phenols, need activation of anhydrides. A wide range of activators engaged for this purpose include various re- agents such as DMAP, 1 Et 3 N, 2 pyridine, 2 4-pyrrolidinopyridine (PPY), 3 and Bu 3 P. 4 A variety of other catalysts such as TaCl 5 , 5a ErCl 3 , 5- b CoCl 2 , 6 ZnCl 2 , 7a ZnO, 7b,c HBF 4 -SiO 2 , 8a ZrCl 4 , 8b,c LiClO 4 , 8d,e Ru-cata- lysts, 8f Mg(ClO 4 ), 8g SmI 2 , 9a Sm(O-Tf) 3 , 9b CeCl 3 , 9c ZrOCl 2 Á8H 2 O, 9d montmorillonite, 9e TMS-Cl, 9f PTSA, 10a distannoxane, 10b ionic liq- uids, 10c , I 2 , 10d,e La(O i Pr) 3 , 11a La(NO 3 ) 3 Á8H 2 O, 11b vanadyl(V)ace- tate, 11c solid supported reagents, 11d lipase enzymes, 11d and various triflates 12a–f have been used for the acylation of alcohols. Acylations with acids, 13a,b acyl imidazoles, 13c and acyl urea 13d are also known. Recently, a variety of new acylation catalysts appeared, for example pentafluorophenylammonium triflate, 14a silica magnesium oxide, 14b polyvinylpolypyrrolidone-bound boron tri- fluoride, 14c N-acyl 1,5-diazabicyclo [4.3.0] non-5-ene tetraphenyl- borate salts, 14d and iron(III)tosylate, 14e and TfOH. 14f Despite the great importance of the above procedure in organic syntheses, it has major drawbacks such as stoichiometric or super stoichiometric amounts of a Lewis acid or Bronsted acid, stringent conditions, long reaction time, formation of side products, cumber- some methodology, incompatibility with other functional groups, use of halogenated solvent, and excess of acylating agents, use of hazardous materials (e.g. DMAP is highly toxic, 14g Bu 3 P is highly flammable and air sensitive 14h ), special effort to prepare the cata- lysts (e.g. Sc(NTf 2 ) 3 , Nafion-H, yttria zirconia,) and in most of the cases being applicable to alcohols only. Hence, the development of a more general, efficient, and environmentally benign catalytic methodology is still of practical importance. The ongrowing acquaintance on assorted issues accompanying environment abuse ascendancy has led to the search for more affa- ble forms of catalysts that display less or no-toxicity to human health and environment. 15 Tris(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ] has received considerable attention as non-conventional, nontoxic, air-stable, water-tolerant, and thermal abiding Lewis acid. 16a Recently, various research groups were engaged in explor- ing the impending efficacy of B(C 6 F 5 ) 3 for various organic transfor- mations, such as ring-opening of epoxides, aza-Ferrier http://dx.doi.org/10.1016/j.tetlet.2014.01.124 0040-4039/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +91 40 23073740; fax: +91 40 23073751. E-mail address: bathini@niperhyd.ac.in (B.N. Babu). R XH B(C 6 F 5 ) 3 (0.5 mol%) (R'CO) 2 O, rt R X R' = -CH 3 , -C 2 H 5 , -Ph R = alkyl or aryl X = O, NH, S R' O Scheme 1. General scheme for acylation of alcohols, phenols, amines, and thiophenols. Tetrahedron Letters 55 (2014) 1784–1787 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet