Pergamon Tetrahedron Letters 39 (1998) 3333-3336 TETRAHEDRON LETTERS Diastereoselective Synthesis of 1,2-Diphenyl-l,2-diaminoethanes by Yb(OTf)3 Accelerated Reductive Coupling of Imines Rita Annunziata, Maurizio Benaglia, Mauro Cinquini, Franco Cozzi, and Laura Raimondi Centro CNR and Dipartimento di Chimica Organica e Industriale - Universita' di Milano via Golgi 19 - 20133 Milano, Italy Received 4 February 1998; accepted 27 February 1998 Abstract New reaction protocols have been established to perform the reductive coupling of N-benzyl benzaldimines to 1,2-diphenyl-l,2-diaminoethanes in mild, stereoselective, and catalytic conditions by the use of SmI2 and Yb(OTf)3. © 1998 Elsevier Science Ltd. All rights reserved. Keywords: Diamines; Reduction; Stereoselection; Lanthanides. The importance of the 1,2-diamine functionality in medicinal chemistry [1,2], stereoselective synthesis [3-6], and analytical chemistry [7,8] prompted a great deal of research toward the development of new methods for the synthesis of these compounds [9- 11]. Among these methods, the metal-promoted reductive coupling of aldimines, although generally limited to the preparation of symmetrical products, is receiving increasing attention[12-20]. Recently, SmI2 [21], that has been extensively exploited for the pinacol coupling of carbonyls [22], proved to be a useful promoter of aldimine coupling, provided that either a large excess of reagent [23-25] or high reaction temperatures [23,24] or very activated aldimines [25] were used. 1 We here report that: i) the combined use of SmI2 and Yb(OTf)3 allows the homocoupling of N-benzyl benzaldimines to occur at room temperature and in the presence of only 2.0 mol 1 The system Sm(0)/Cp2TiCI2 has also been used [26] for imine coupling, but it is likely that in this case the reaction is promoted by an in situ generated Ti(lll) species. For a similar example in carbonyl pinacol coupling see ref. [27]. 0040-4039/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PH: S0040-4039(98)00484-5