Original articlePEG–SO3H as an efficient and reusable catalyst for chemoselective synthesis of 1,1-diacetates
Graphical abstract
The synthesis of 1,1-diacetates from aromatic aldehydes and acetic anhydride in the present of PEG–SO3H as efficient catalyst is described. The catalyst can be recovered and reused eight times.
Introduction
The synthesis of 1,1-diacetates is one of the most versatile acylal-formation reactions in modern organic synthesis. Since 1,1-diacetates are stable toward a wide range of nucleophiles under neutral and basic conditions, acetylation is commonly utilized as a protecting method for carbonyl groups [1]. Moreover, they also serve as valuable precursors for the asymmetric allylic alkylation reactions [2] in natural product synthesis [3], and for the synthesis of 1-acetoxydienes and 2,2-dichlorovinylacetates for Diels–Alder reactions [4], [5]. Acylals have also been used as cross-linking agents for cellulose in cotton [6]. Therefore, the methods for their synthesis have received considerable attention. Generally, 1,1-diacetates are synthesized from aldehydes and acetic anhydride using a variety of protic acids such as methanesulfonic [7], sulfuric [5], or perchloric acid [8]. However, in many cases, the yields are poor.
Recent years have witnessed the intensive investigation of this reaction using various Lewis acids such as Fe(NO3)3·9H2O [9], cupric sulfate [10], In(OTf)3 [11], P2O5/Al2O3 [12], LiOTf [13], Bi(NO3)3 [14], Al(HSO4)3 [15]. Several reusable heterogeneous catalysts for the reaction have also been reported such as titanium modified MCM-41 [16], Keggin heteropolyacid [17], sulfuric acid [3-(3-silicapropyl)sulfanyl]propyl ester [18], silica-bonded N-propylsulfamic acid [19], polymer-supported gadolinium triflate [20], silica-bonded S-sulfonic acid [21], ZSM-5-SO3H [22], different solid acids [23], solid silica sulfuric acid [24], and Brønsted acidic ionic liquids under ultrasonic irradiation [25].
Although some of these methods afford good to high yields of the corresponding diacetates, the majority suffers from one or more of the following limitations: prolonged reaction time or low yields, high temperature, use of harmful organic solvents, or use of moisture-sensitive and costly catalysts. Previously, our group has reported the Biginelli-type reaction using PEG–SO3H as a catalyst and solvent under microwave irradiation [26]. The PEG–SO3H catalyst is water-stable, non-corrosive, environmentally benign and recyclable [27], [28].
In order to continue our work, based on our previous research [26], [29], [30], herein, we wish to describe PEG–SO3H as a catalyst for the synthesis of aromatic 1,1-diacetates.
Section snippets
Experimental
All reagents were obtained from commercial vendors and used without further purification. Melting points were determined on an XT-4 electrothermal micromelting point apparatus and the thermometer was uncorrected. PEG–SO3H was prepared according to the previously reported procedure [26]. IR spectra were recorded using KBr pellets on Nicolet AVATAR 36 FT-IR spectrophotometer. NMR spectra were recorded at 400 (1H) and 100 (13C) MHz, respectively, on a Varian Mercury plus-400 instrument using CDCl3
Results and discussion
The PEG-bound sulfonic acid catalyst was prepared by reacting PEG-6000 with excess chlorosulfonic acid according to the literature procedures [27]. The conversion of the terminal hydroxyl groups on the PEG was determined to be quantitative by 1H NMR analysis (Fig. S1, see supporting information), and the singlets at δ 12.85 and 4.23 were assigned to the proton of SO3H and the α-methylene protons at the polymer attached site, respectively. The IR spectra of PEG–SO3H and PEG6000 are illustrated
Conclusion
The reactions to synthesize 1,1-diacetates from aldehydes and acetic anhydride were efficiently catalyzed by PEG–SO3H under solvent-free conditions. The catalyst can be recovered and reused at least eight times without apparent loss of activity. It should be noted that PEG–SO3H has high catalytic activity, and that only 5 mol% of PEG–SO3H is sufficient to catalyze the reaction in most cases. These results not only provide a new aspect of catalytic organic reactions, but also extend the utility
Acknowledgments
This work was financially supported by Key Laboratory of Hexi Corridor Resources Utilization of Gansu Universities (No. XZ1011), the President's Funds of Hexi University (No. XZ-2009-9) and the National Natural Science Foundation of China (No. 21262010).
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Sulfonated poly(4-vinylpyridine) heteropolyacid salts: A reusable green solid catalyst for Mannich reaction
2014, Chinese Chemical LettersCitation Excerpt :Most recently, we have reported the preparation of sulfonated poly(4-vinylpyridine) heteropolyacid salts (Scheme 1) and used it as a catalyst for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones under ultrasonic irradiation (Scheme 2) [46]. In continuation of our work to develop new catalysts for organic transformations [46–48], here we report the synthesis of β-amino carbonyl compounds in the presence of sulfonated poly(4-vinylpyridine) heteropolyacid salts (Scheme 3). Melting points were determined on a Perkin-Elmer differential scanning calorimeter, and the temperature was uncorrected.