Selective Diethylzinc Reduction of Imines in the Presence of Ketones Catalyzed by Ni(acac)₂

Abstract

A selective reduction method of an electronically deficient imine in the presence of ketone was developed by employing Et(2)Zn and 5 mol % of Ni(acac)(2). The method was applied in the reduction of S(S)-tert-butanesulfinyl ketimines 1 to afford amines 2 in 23-92% yields and 73:27 to 98:2 diastereoselectivities. A plausible mechanism was proposed on the basis of an NMR study.

A Versatile Ru Catalyst for the Asymmetric Transfer Hydrogenation of Both Aromatic and Aliphatic Sulfinylimines

“…The diastereoselective reduction of N-(tert-butylsulfinyl)ketimines has been achieved by using several boranes, [30b,c, 32] sodium or lithium borohydrides, [30b,c,h, 32, 33] aluminum hydrides, [30c, 32, 33] and diethylzinc in the presence of NiA C H T U N G T R E N N U N G (acac) 2 (acac = acetyl-A C H T U N G T R E N N U N G acetonate). [34] However, the hydrogen-transfer protocol had never been applied to the stereoselective reduction of this kind of imine until we reported the first ATH of N-(tert-butylsulfinyl)ketimines in isopropyl alcohol catalyzed by a ruthenium complex bearing (1S,2R)-1-amino-2-indanol as a chiral ligand. [35] Very high enantiomeric excesses were obtained with a variety of aromatic sulfinylimines.…”

Synthesis of Highly Enantiomerically Enriched Amines by Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)Imines

“…The asymmetric reduction of this type of imine has been performed using boranes, 6a,6b,7 sodium or lithium borohydrides, 6,7,8 aluminium hydrides, 6b,7,8 and diethylzinc in the presence of Ni(acac) 2 . 9 The present procedure utilizes a methodology based on asymmetric transfer hydrogenation, which is a very convenient reduction protocol because it avoids the handling of molecular hydrogen or metallic hydrides, among other reasons. Thus, highly enantiomerically enriched -branched primary amines are obtained in excellent yields by the diastereoselective reduction of a variety of sulfinylimines followed by desulfinylation of the nitrogen atom.…”

Microwave‐Enhanced Asymmetric Transfer Hydrogenation of N‐(tert‐Butylsulfinyl)imines

“…General Procedure for the Synthesis of Imines 1 and ent ‐1: N ‐( tert ‐Butylsulfinyl)ketimines were prepared by condensation of the corresponding ketones with ( R )‐2‐methylpropane‐2‐sulfinamide (for 1 ) or ( S )‐2‐methylpropane‐2‐sulfinamide (for ent ‐ 1 ) following our reported procedure 10b. Imines 1a ,13 1b ,13 1c ,14 1d ,15 1e ,8d 1f ,13 1g (R 1 = 4‐BocNHC 6 H 4 ),8b 1h ,8b 1i ,16 1j ,15 1k ,17 1l ,18 1m ,19 1n ,8d 1o ,8b 1p ,8d 1q ,8d ent ‐ 1a 15 and ent ‐ 1r 8b were identified by comparison of their physical and spectroscopic data with those reported in the literature.…”