Cooperative Cation Binding Catalysis For Direct Generation Of Two Contiguous Tertiary And Quaternary Stereogenic Centers
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Abstract In this study, the concept of cooperative cation binding catalysis was elegantly applied for direct generation of two contiguous tertiary and quaternary stereogenic centers. Using a highly accessible chiral oligoethylene glycol (oligoEG) as a cation-binding catalyst, asymmetric Mannich reaction of α-thiocyanato cyclic ketones as Mannich donors was performed with α-amido sulfones as the bench-stable imine precursors in the presence of potassium fluoride as the base, affording α-thiocyanato-β-amines possessing tetra-substituted C-SCN centers. The salient features of this process include (a) a transition-metal free and operationally simple procedure, (b) direct use of α- amido sulfones as bench-stable precursors of sensitive imines,…show more content… In particular, chiral compounds with β-amino-α-thiocyanate moieties are rarely explored in the medicinal chemistry area because of their synthetic difficulty, although they are versatile precursors for the synthesis of β-aminothiols, β-aminosulphonic acids, and 2-iminothiazolidines, present in some stereoselective catalysts, and many biologically and pharmacologically active compounds.
To the best of our knowledge, only three related publications have been reported to date.[9,10] In 2013 Sala et al.[10a], and Babu and Parquette[10b] independently reported the asymmetric synthesis of β-amino-α-thiocyanate compounds via the desymmetrization of meso-aziridines with TMSNCS using combined Ca(II)/Mg(II) VAPOL phosphate salts and chiral dimeric yttrium-salen complexes as catalysts. Quite recently, Nakamura et al. also reported the same transformation using chiral imidazoline−phosphoric