Methylene‐Bridged Bis(imidazoline)‐Derived 2‐Oxopyrimidinium Salts as Catalysts for Asymmetric Michael Reactions

Abstract

In nothing flat: The title salts, having planar nitrogen centers, were utilized successfully as phase‐transfer catalysts for asymmetric Michael reactions of tert‐butyl glycinate benzophenone Schiff base with vinyl ketone and chalcone derivatives, thus providing excellent levels of diastereo‐ and enantiocontrol (see scheme).

Application of aziridinium ring opening for preparation of optically active diamine and triamine analogues: highly efficient synthesis and evaluation of DTPA-based MRI contrast enhancement agents

“…Vicinal diamines 7 19 and 10 21 were readily obtained from removal of N -benzyl groups in compounds 5 and 6 by hydrogenolysis, respectively. To further confirm regiochemistry and stereochemistry in the ring opening products 5 , the known N -methyl vicinal amine 9 20 was prepared from 5 (Scheme 2). Reaction of 5 with dimethyl sulfate provided compound 8 , and N -benzyl groups in 8 were selectively removed by reaction of ammonium formate in the presence of Pd/C to produce 9 .…”

Recent advances of organocatalytic enantioselective Michael-addition to chalcone

“…Hii et al [19] in 2013 independently reported an efficient asymmetric Michael addition of glycine imine ester 51 to chalcones 52 by utilizing 2-oxopyrimidinium salt 12 as catalyst. The reaction proceeded in high yields with high enantioselectivity (Scheme 13).…”

A Polystyrene‐Supported Phase‐Transfer Catalyst for Asymmetric Michael Addition of Glycine‐Derived Imines to α,β‐Unsaturated Ketones

“…In 2005, Ishikawa et al. performed an asymmetric conjugate addition using polymer‐supported chiral guanidines . Hii et al.…”

“…Hii et al. reported asymmetric Michael reactions using 2‐oxopyrimidinium salt 1 as a homogeneous catalyst with a novel structure (Figure ), achieving high yields and high enantioselectivities under mild conditions …”