Abstract
‘Desymmetrization’ of trans-1,2-diaminocyclohexane by treatment with α,ω-dihalogenated alkylation reagents leads to mono-NH2 derivatives (‘primary-tertiary diamines’). Upon reaction with formaldehyde, these products formed monomeric formaldimines. Subsequently, reactions of the formaldimines with α-hydroxyiminoketones led to the corresponding 2-unsubstituted imidazole N-oxide derivatives, which were used here as new substrates for the in situ generation of chiral imidazol-2-ylidenes. Upon O-selective benzylation, new chiral imidazolium salts were obtained, which were deprotonated by treatment with triethylamine in the presence of elemental sulfur. Under these conditions, the intermediate imidazol-2-ylidenes were trapped by elemental sulfur, yielding the corresponding chiral non-enolizable imidazole-2-thiones in good yields. Analogous reaction sequences, starting with imidazole N-oxides derived from enantiopure primary amines, amino alcohols, and amino acids, leading to the corresponding 3-alkoxyimidazole-2-thiones were also studied.
Highlights
Since 1991, after the isolation of the first stable 1,3-di(adamantyl)imidazol-2-ylidene [1], there has been a wealth of both structural studies and practical applications of nucleophilic N-heterocyclic carbenes (NHCs) [2,3]
We demonstrated that 2-unsubstituted imidazole N-oxides including some skeleton
In a very recent publication, we reported the synthesis of non-symmetric imidazolium salts prepared in a multistep synthesis starting with adamantyloxyamine [24]
Summary
Since 1991, after the isolation of the first stable 1,3-di(adamantyl)imidazol-2-ylidene [1], there has been a wealth of both structural studies and practical applications of nucleophilic N-heterocyclic carbenes (NHCs) [2,3]. There is continuing demand for catalysts and ligands for asymmetric synthesis [4]. Chiral NHCs are suitable for such applications, and the elaboration of methods for the preparation of their precursors and subsequent applications in asymmetric synthesis are intensively pursued [5,6,7,8]. One efficient method for the preparation of chiral. Molecules 2019, 24, 4398; doi:10.3390/molecules24234398 www.mdpi.com/journal/molecules are limited [6]. Chiral β-amino alcohols and amino esters have scarcely been explored. Derivatives of type 1 with a cyclic amine motif are promising
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
