Abstract
Multicomponent reactions are excellent methods that meet the requirements of green chemistry, by reducing the number of steps, and consequently reducing purification requirements. Accordingly, in this work, 11 novel hybrid-boron-containing molecules, namely eight 1,4-dihydropyridines and three 3,4-dihydropyrimidinones, derived from formylphenylboronic acids (ortho, meta and para), were obtained using a green approach, involving H-4CR and B-3CR practices, in the presence of ethanol, which is a green solvent, and using three comparatively different modes of activation (mantle heating, yield 3%–7% in 24 h, Infrared Radiation (IR) irradiation, yield 12%–17% in 12 h, and microwave irradiation, yield 18%–80%, requiring very low reaction times of 0.25–0.33 h). In addition, as a green-approach is offered, a convenient analysis, of the 12 green chemistry principles for the overall procedure was performed. Finally, since all the products are new, characterizations were carried out using common analytic procedures (1H, 11B, and 13C NMR, FAB+MS, HRMS, and IR). The accurate mass data of unexpected ions related to interactions between thioglycerol and the expected products, in the FAB+-mode, enabled unequivocal characterization of the target molecules.
Highlights
The design and implementation of new sustainable synthetic processes is one of the major challenges in modern organic synthesis
Multicomponent reactions (MCR) are an important subclass of tandem reactions. These reactions are suitable for green organic syntheses because they involve processes in which three or more components react directly to form a unique product, giving good atom economy [1,2,3,4]
As part of our ongoing research program on the production of biologically active heterocyclic molecules using suitable green approaches, using mainly novel modes to activate reactions [15,16,17,18,19], we report, in this article, the development of 11 new boron-containing heterocyclic molecules
Summary
The design and implementation of new sustainable synthetic processes is one of the major challenges in modern organic synthesis. The MCRs, known as “one-pot” processes, are valuable in green organic synthesis because they have many important attributes: A small number of steps, and a simple purification procedure, which enhances the synthetic efficiency, and savings in time, solvents, and other resources These features are in agreement with following Principles of Green Chemistry [5]: prevention (principle 1), the formation of by-products is minimum; atom economy (principle 2), the target methodology is designed to maximize the incorporation of the atoms in the starting materials, into the final product; safer solvents and auxiliaries (principle 5), it is unnecessary to use solvents for intermediate purification, avoiding the generation of waste; design for energy efficiency (principle 6), the use of alternative modes of activation of a particular reaction e.g., microwave or infrared irradiation, instead of typical thermal procedures (mantle heating), significantly reduces the corresponding reaction times, decreasing energy consumption; reduce derivatization (principle 8), unnecessary derivatization is avoided (the use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes); catalytic processes (principle 9), in many cases eco-friendly catalysts are used; and some others, depending on the specific case
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