Synthesis of Fatty Acetoacetates Under Microwave Irradiation Catalysed by Sulfamic Acid in a Solvent‐Free System

Abstract

of polymers, drugs and biologically active compounds [1][2][3]. They have also been studied as biofuel additives [4].Using acetoacetates as the building blocks in multicomponent reactions (MCR) [5] yields several different structures based on the dihydropyridinone (DHPM) or dihydropyridine (DHP) skeleton, which creates an extensive library of compounds with various biological activities [6-10]. MCR have been recognized for their high convergence, atomic economy and operational simplicity and are emphasized as important tools to synthesize high-molecular-complexity compounds in accordance with green chemistry principles [2,11].The transesterification reaction to synthesize acetoacetates is a notably useful tool in organic synthesis, and various methods have been reported to affect the transesterification of methyl or tert-butyl acetoacetates. The uncatalyzed transesterification of acetoacetates requires the use of either an excess of ketoester or a longer reaction time and a high boiling alcohols or solvents limiting their usage [12].According to the literature, the transesterification process to synthesize β-ketoesters under solvent-free conditions without catalysis results in high yields when excess alcohol is used at a high temperature [13]. In addition, the rate of transesterification of acetoacetates is significantly affected by steric factors; thus, tertiary alcohols are less active. Primary, secondary, and tertiary alcohols have been tested in the presence of molecular sieves, which results in good acetoacetate yields [12]. The catalysts in the transesterification reaction vary and include new silica-based hybrid materials, triethylamine, boric acid, and triphenylphosphine [14][15][16][17].However, the development of a new method that enables transesterification in milder conditions should heighten the synthetic potential of the reaction. Considering the importance of acetoacetates, cleaner methodologies have been studied for their synthesis; solvent-free conditions [18] and replacement of catalysts [13] render the protocol to obtain Abstract The 1,3-dicarbonyl compounds are important building blocks to obtain products with various biological activities and technological applications. In this work, we used a simple transesterification method to develop fatty acetoacetates in a solvent-free medium using a green catalyst, sulfamic acid (NH 2 SO 3 H), under microwave irradiation. The experimental results demonstrate good yields in a short reaction time (13 min), which makes this method an efficient approach to synthesize fatty acetoacetates from a wide range of saturated, unsaturated, and polyunsaturated long chain fatty alcohols, and ricinoleic derivatives. Experiments of recycling of the catalyst were performed and no decrease in catalytic activity of sulfamic acid was observed.

Evaluation of the antioxidant activities of fatty polyhydroquinolines synthesized by Hantzsch multicomponent reactions

“…Initially, fatty alcohols and fatty acids were used as precursors to synthesize fatty b-ketoesters (FBKEs) using previously reported methods. 29,30 FBKEs 1a, 1b and 1c were synthesized by the transesterication of methyl acetoacetate from palmitic (C16:0), stearic (C18:0), and oleyl (C18:1) alcohols, respectively. At the same time, the FBKE precursors 2a, 2b and 2c were synthesized via Meldrum's acid acylation with the corresponding fatty acids, followed by a decarboxylation step using methanol (Scheme 1).…”

Recent advances in the transesterification of β-keto esters

“…Weber et al have recently reported the synthesis of long chain acetoacetates via sulfamic acid catalysis under solvent-free conditions ( Table 66 ). 150 Using microwave irradiation, the reaction time was reduced from 6 hours to 13 minutes. The yields obtained via conventional heating or microwave irradiation were comparable.…”