Stereocontrol in the reduction of 1,2-diimine with an oxazaborolidine catalyst. Highly stereoselective preparation of (R,R)-1,2-diphenylethylenediamine

The Chemistry of Vicinal Diamines

“…The catalytic asymmetric reduction of 1,2-bis(para-methoxyphenylimino)-1,2-diphenylethane (392) was recently reported by Fujisawa et al [169] (Scheme 95). An oxazaborolidine, obtained from l-threonine derivative 393, served as the catalyst in a process that afforded selectively the syn-diamine 394 in excellent yield.…”

Asymmetric Imine Hydroboration Catalyzed by Chiral Diazaphospholenes

“…Reports of asymmetric reductive amine formation with Corey-Bakshi-Shibata catalyst/Itsuno-type reagents fre-quently require stoichiometric quantities of amino alcohol ligand, or very electron-poor imines,f or high conversion or enantioselectivity unless the substrate is an oxime. [10][11][12] In amore recent development, Du and co-workers reported the asymmetric reduction of aryl imines with ammonia borane, employing 10 mol %o fa na dduct between Ellmansc hiral sulfinimide and Piers borane as ac atalyst (Scheme 1). [13] A report by Enders and co-workers describes the use of achiral Brønsted acid for imine reduction employing catecholborane as the terminal reductant (Scheme 1), with aryl a-imino ester substrates giving optimal enantioinduction.…”

Synthesis of Highly Substituted 2-13C-Imidazolium Salts and Metal NHC ­Complexes for the Investigation of Electronic Unsymmetry by NMR

“…The solvent was removed in vacuo and the crude product was purified by flash chromatography (silica gel, CH 2 Cl 2 -MeOH, 20:1 to 5:1) to give 9g as a colorless solid; yield: 23.8 mg (28% over 2 steps); mp 290 °C (dec); R f = 0.13 (CH 2 Cl 2 -MeOH, 10:1). N 1 ,N 2 -Bis(4-ethoxyphenyl)-1,2-diphenylethane-1,2-diimine (10) Prepared according a procedure of Shimizu et al 27 A soln of benzil (7.50 g, 35.7 mmol) and p-phenetidine (4.90 g, 35.7 mmol) in 1,2dichloroethane (70 mL) was stirred at 70 °C for 72 h. The soln was filtered and the solvent was removed in vacuo. The crude product was recrystallized (MeOH, 200 mL) to give 10 as yellow crystals; yield: 10.4 g (66%); mp 149.1-149.3 °C; R f = 0.32 (cyclohexane-EtOAc, 10:1).…”