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Preparation of Di(2-hydroxybenzylamines) by Reduction of Disalicylimines

IP.com Disclosure Number: IPCOM000029302D
Publication Date: 2004-Jun-22
Document File: 2 page(s) / 39K

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WO 03/002255 A1: PATAPP

Abstract

Di(2-hydroxybenzylamines), II, can be prepared from the corresponding disalicylimines, I, by either borohydride reduction or hydrogenation with heterogeneous transition metal catalysts. In either case, the disalicylimines can be prepared in situ from the amine and substituted salicyladehyde and then reduced. The addition of acids, such as acetic acid, or bases, such as cesium carbonate, can improve the performance of the heterogeneous metal catalyst system.

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Preparation of Di(2-hydroxybenzylamines) by Reduction of Disalicylimines

Abstract: Di(2-hydroxybenzylamines), II, can be prepared from the corresponding  disalicylimines, I, by either borohydride reduction or hydrogenation with heterogeneous transition metal catalysts.  In either case, the disalicylimines can be prepared in situ from the amine and substituted salicyladehyde and then reduced.  The addition of acids, such as acetic acid, or bases, such as cesium carbonate, can improve the performance of the heterogeneous metal catalyst system.

            Di(2-hydroxybenzylamines) of the general structure II are useful chelating ligands for a variety of metals and also provide useful asymmetric catalysts when the diamine linkage N-J-N is chiral.  The N-J-N diamine linkage can be derived from any primary diamine (i.e. NH2-J-NH2)  including ethylenediamine, 1,2-diaminocyclohexane, and 1,2-diphenylethylenediamine.  When the primary diamine contains chiral centers it may be chiral or meso.  The aryl substituents, R, include most typical substituents.  Sterically demanding aryl substituents such as adamantyl, 2-propyl, t-butyl, and trimethylsilyl are of particular interest.

The preparation of compounds of structure II can be achieved by reduction of disalicylimines of general structure I with borohydride reagents (eq 1). Effective borohydride reagents include sodium cyanoborohydride, sodium triacetoxyborohydride and sodium borohydride.  A minimum of two B-H molar equivalents is required to achieve complete conversion of I, but excess borohydride is usually needed, therefore between two to twelve B-H equivalents is typically used. Alcohol, ether, and aromatic solvents, such as methanol, ethanol, tetrahydrofuran, toluene, and xylene, or mixtures of these solvents, are suitable for the reduction.  Convenient reaction temperatures can range from 0 to 100 ºC, but are preferably between 35 to 80 ºC.  Reaction times can vary from about 3 to 24 hours.  Isolation of the product benzylamines of structure II depends on the nature of the R and J groups, but crystallization from alcohol or water/alcohol mixtures is often effective. 

           

            The borohydride reductions described above can be effective when applied to either preformed I or to reaction mixtures in which I has been formed in situ.  For example, disalicylimines of structure I can be readily prepared by condensation of aldehydes of structure III with diamines of structure IV (eq 2).  Therefore, the addition of borohydride reagents to reaction mixtures containing III and IV can be an effective route to II. Competitive reduction of the aldehyde III can be minimized by first removing water from the reaction system a...