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Chiral picolylamines for Michael and aldol reactions: probing substrate boundaries†
Thomas C. Nugent,Ahtaram Bibi,Abdul Sadiq,Mohammad Shoaib,M. Naveed Umar,Foad N. Tehrani
Organic & Biomolecular Chemistry Pub Date : 10/09/2012 00:00:00 , DOI:10.1039/C2OB26382C
Abstract

Here we report on inroads concerning increased substrate breadth via the picolylamine organocatalyst template, a vicinal chiral diamine based on a pyridine-primary amine motif. The addition of cyclohexanone to β-nitrostyrene has many catalyst solutions, but cyclopentanone and isobutyraldehyde additions continue to be challenging. PicAm-3 (10 mol%) readily allows the Michael addition of cyclopentanone or isobutyraldehyde (5.0 equiv.) to β-nitrostyrene derivatives. By contrast, PicAm-1 (7.0 mol%) is optimal for catalyzing the aldol reaction of cyclohexanone or cycloheptanone (3.3 equiv.) with aromatic aldehydes. Eighteen products are reported and for each reaction type new products are reported (4b–d, 9c). Very good yields and stereoselectivities are generally noted. The reactions, which require an acid additive, proceed via a transient chiral enamine and a mechanistic case is put forth for a bifunctional catalysis model.

Graphical abstract: Chiral picolylamines for Michael and aldol reactions: probing substrate boundaries
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