Synthesis of 1,2 diamines under environmentally benign conditions: application for the preparation of imidazolidiniums Stéphane P. Roche a,b,  , Marie-Laure Teyssot b , Arnaud Gautier b,c, * a Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA b Clermont Université, Université Blaise Pascal, Laboratoire SEESIB, BP 10448, F-63000 Clermont-Ferrand, France c CNRS, UMR 6504, SEESIB, 24 Avenue des Landais, F-63177 Aubière CEDEX, France article info Article history: Received 23 November 2009 Revised 9 December 2009 Accepted 11 December 2009 Available online 21 December 2009 Keywords: 1,2-Diamines Imidazolidinium abstract An environmentally friendly and economically attractive access to unsymmetrical and symmetrical 1,2- diamines has been developed. Chemoselective N-monoalkylation in water and alcoholic solvents was demonstrated. This method represents a simple and scalable preparation (2–3 steps) of symmetrical and unsymmetrical imidazolidinium salts, precursors of N-Heterocyclic Carbenes. Ó 2009 Elsevier Ltd. All rights reserved. The replacement of classical organic solvents by environmen- tally friendly reaction media is of contemporary attention. Water and alcohols are ideally suited for industrial purpose due to their nontoxic character. Indeed, water has special characteristics which are not encountered with other solvents such as high thermal capacity, hydrophobic association, high polarity, and hydrogen- bonding ability. 1 Due to these properties, reactions in and ‘on’ water often show higher reaction rates, better selectivity and yields than those performed in classical organic solvents. 2 Within the course of a research program in the field of metal-N- Heterocyclic Carbenes (NHCs) devoted to biological applications and click reaction catalysis, 3 a fast synthesis of various imidazolid- inium cations was needed. NHCs, that constitute an important class of ligand for multiple catalyzed chemical transformations, 4 are generally obtained from their imidazolidinium precursors 1a– b. The symmetrical imidazolidiniums 1a are classically obtained in three steps: azadiene 3 formation from glyoxal 5 condensation with a primary amine 6 followed by reduction yielding 1,2-dia- mine 2a and cyclization (Scheme 1). 5 The unsymmetrical imidazo- lidinium 1b results from a sequential addition of two different amines (6 and 13) to methyl oxalyl chloride 6 10 or chloroacetyl chloride 7 14 followed by reduction to access to the unsymmetrical 1,2-diamine 2b (Scheme 1). 8 In all cases, an oxidation level adjust- ment along the synthesis is needed. Unfortunately this step proved to be often problematic. We postulated that both symmetrical and unsymmetrical 1,2 secondary diamines 2a–b could be accessed di- rectly, avoiding any reduction step, from substitution on 1,2-diha- logenoethane 7 or halogenoethylammonium 15 by substitution reactions in one or two steps, respectively. We were then facing the challenging preparation of symmetrical and unsymmetrical 1,2-diamines 2a–b in one or two steps, respectively. 0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2009.12.072 * Corresponding author. Tel.: +33 473 407 646; fax: +33 473 407 717. E-mail address: Arnaud.Gautier@univ-bpclermont.fr (A. Gautier).   Present address: Department of Chemistry, Boston University, 590 Common- wealth Avenue, Boston, Massachusetts 02215, USA. NR ArN NAr ArN X NR ArN NAr ArN X NHAr ArHN NHR ArHN NHR ArHN O O X Ar Ar N N NH 2 ArHN 2 HX ArNH 2 OMe ArHN O O NH 2 Ar X X ArNH 2 NH 3 X X O O ArNH 2 O O Cl OMe + 15 6 16 + + 2b + 2b Previous literature report 2a 2a 1b X 1a NHR ArHN O Cl ArHN O ArNH 2 O Cl Cl + or This work Previous literature report 1a This work 1b 3 5 6 6 7 8 9 10 6 11 12 14 6 + RNH 2 13 NHAr ArHN NHR ArHN Scheme 1. Symmetrical and unsymmetrical imidazolidiniums retrosynthesis. Tetrahedron Letters 51 (2010) 1265–1268 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet