B2O3/Al2O3 as a new, highly efficient and reusable heterogeneous catalyst for the selective synthesis of β-enamino ketones and esters under solvent-free conditions

Abstract

Óxido de boro adsorvido sobre alumina (B 2 O 3 /Al 2 O 3 ) foi usado como um novo e eficiente catalisador na síntese de β-aminocetonas e ésteres pela enaminação de diferentes aminas primárias e secundárias com compostos carbonílicos sob condições livre de solvente. A importância dessa metodologia congrega grande variedade de substratos, alta eficiência, ausência de catalisador metálico, alta régio-e quimioseletividade em condições amigáveis ao ambiente. Ainda, o catalisador pode ser recuperado facilmente depois das reações e reusado sem perda de atividade.Boron oxide adsorbed on alumina (B 2 O 3 /Al 2 O 3 ) has been found to be a new and highly efficient heterogeneous catalyst for the synthesis of β-enamino ketones and esters by the enamination of various primary and secondary amines with β-dicarbonyl compounds under solvent-free conditions. The important features of this methodology are broad substrate scope, high yield, no requirement of metal catalysts, high regio-and chemoselectivity and environmental friendliness. In addition, the catalyst could be recovered easily after the reactions and reused without evident loss of reactivity.Keywords: β-enamino ketones, β-enamino esters, β-dicarbonyl compounds, amines, B 2 O 3 /Al 2 O 3 , solvent-free Introduction β-Enamino carbonylic compounds represent an important class of functionalized building blocks, which become increasingly important in medicinal chemistry and organic synthesis.1 Consequently, various approaches toward the construction of β-enamino carbonylic compounds have been explored during the past years. The direct enamination of 1,3-dicarbonyl compounds with amines is one of the most straightforward methods for the synthesis of β-enamino ketones and esters in the presence of various promoting agents.2-19 Recent reports have described the preparation of β-enamino ketones and esters catalyzed by metal triflate. 20 Although the reported methodologies are suitable for certain synthetic conditions, some of these procedures suffered from disadvantages, such as long reaction time, low yield, use of volatile organic solvents, requirement of excess of reagents or costly catalysts, special apparatus and harsh reaction conditions. Therefore, the development of convenient, environmental friendliness, high yield and clean approaches is highly desirable.Recently, heterogeneous organic reactions 21 have been recently performed with immobilized reagents on solid supports. These procedures offer several intrinsic advantages such as clean reactions, the easy separation of products, the recover and reuse of catalyst conveniently, the minimization of waste production, and eco-friendliness etc.As a part of our great interest in developing novel synthetic routes for the formations of carbon-carbon and carbon-heteroatom bonds, 22 we herein reported B 2 O 3 /Al 2 O 3 as a new, efficient and reusable heterogeneous catalyst for the enamination of β-dicarbonyl compounds with amines. Results and DiscussionThe model reaction of ethyl acetoacetate (1a) with aniline (2a) was conducte...

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

“…The acceptor amide as acceptor clearly leads to the weaker hydrogen bond. [15,26]. For the corresponding N-methyl derivatives, the chemical shifts are 10.90 ppm and 8.55 ppm.…”

“…A classic comparison is that of hydrogen bonding involvin seen in Figure 5A,B [15,26]. For the corresponding N-methyl derivatives, the ch ppm and 8.55 ppm.…”

A Mild and Efficient Method for Synthesis of b-Enaminones using Melamine-Formaldehyde Resin Supported H+ Under Solvent Free Conditions

“…The conventional route for the synthesis of enaminones is condensation between 1,3dicarbonyls and amines. Various catalysts have been used to affect the synthesis of β-enaminones: these include the use of β-cyclodextrin 7 , ytterbium triflate 8 , HClO 4 •SiO 2 9 , silica chloride 10 , B 2 O 3 /Al 2 O 3 11 , NaHSO 4 /SiO 2 12 , dilute HCl 13 , [(PPh 3 )AuCl]/AgOTf 14 , bismuth(III) trifluoroacetate 15 , molecular iodine 16 , Amberlyst-15 ®17 , zeolite (ZSM-5) 18 , CoCl 2 •6H 2 O 19 , silica sulphuric acid 20 and ferric(III) ammonium nitrate 21 . Some of these synthetic approaches suffer from harsh reaction conditions, long reaction time, use of costly catalysts and volatile organic solvents and low to moderate yields.…”

Boron Trioxide–Alumina as a Heterogeneous Catalyst in a Facile Solvent Free One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-Ones

“…23 These procedures offer several intrinsic advantages such as clean reactions, easy separation of the products, the recovery and reuse of catalyst, and the minimisation of waste production. To the best of our knowledge, only two examples have been described in which B 2 O 3 /Al 2 O 3 as a heterogeneous catalyst has been used for the synthesis of β-amino alcohols 24 and β-enamino ketones/esters 25 in the field of organic synthesis.…”