Abstract
<p>An efficient and highly eco-friendly protocol for the preparation of <em>N,N´</em>-dibenzyl or <em>N,N´</em>-(2-hydroxybenzyl)diamines via the reduction of the corresponding di-Schiff bases that produces a good yield using water as a solvent without the need for catalysis or the azeotropic removal of water has been developed. These symmetric diimines have been reduced to their corresponding diamines with sodium borohydride using a catalyst- and solvent-free protocol with excellent yield. Mild conditions, high yields, and a simple work-up procedure are the primary benefits of this protocol.</p>
Highlights
The synthesis of cyclic amines from a carbonyl compound and a diamine is currently the method of choice for the preparation of these compounds
In addition to interest in the stereochemical properties of these compounds and interest in their application in the asymmetric synthesis of ligands in catalysis, N,N-bis(2-hydroxybenzyl) (2) and N,N-dibenzyl (3) derivatives of 1,2, and 1,3-diamines are of biological importance because their derivatives with related structures act as analgesics, antiparasitics, antifungals, and antibacterials (Bisceglia, Díaz, Torres, & Orelli, 2011)
Respective di-Schiff bases 10e-p obtained from this process were further successfully reduced with sodium borohydride under catalyst-free and solvent-free conditions (Wang, Tang, Pan, Yang, & Zhang, 2015), producing the corresponding tetrahydro-di-Schiff bases 11e-p (Scheme 1)
Summary
The synthesis of cyclic amines from a carbonyl compound (aldehyde or ketone) and a diamine (or derivative) is currently the method of choice for the preparation of these compounds. Given our interest in the development of greener synthetic pathways, our synthesis started with the preparation of imines 10e-p using a simple water-mediated procedure that require neither a catalyst nor any additive (Koteswara Rao et al, 2010) and the products were isolated by filtration. Most conventional imine reaction methods described to date involve treatment with reducing agents such as NaBH4 in an organic solvent, such as ethanol or methanol, with the use of catalysts during reflux (Abdel-Magid, 2014). In many cases, solid-state organic reactions occur more efficiently and more selectively than do their counterparts in solution; solvent-free reactions have many advantages: reduced pollution, low cost, and simple processing and handling (Tanaka & Toda, 2000). In this work we report an alternative, simple solvent-free procedure for the synthesis of tetrahydro-di-Schiff bases that uses sodium borohydride as a reducing agent
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