The
highly regio-, diastereo-, and enantioselective dearomatization
reaction of 1-substituted 2-naphthols and β,γ-alkynyl-α-imino
esters with complete atom economy is disclosed via chiral phosphoric
acid catalysis. This protocol provides facile and efficient access
to asymmetric construction of a broad range of axially chiral allene-derived
naphthalenones bearing quaternary stereocenters in good yields with
high diastereoselectivities and enantioselectivities.
The discovery of enantioselective desymmetrization reactions to provide practical synthesis of enantio-enriched atropisomeric biaryls is a challenging topic in the field of asymmetric catalysis. Herein, we report a highly enantioselective desymmetrization reaction for the synthesis of axially chiral biaryl N-oxides by atroposelective CÀ H iodination by using Pd(II) coordinated by N-benzoyl-l-phenylalanine as a chiral catalyst at room temperature. A broad range of products were obtained in high yields (up to 99 %) with excellent enantioselectivities (up to 98 % ee). The products could be synthesized in gram scale, one of which was proved to be a powerful organocatalyst in asymmetric allylation reaction. Mechanistic evidence as well as DFT calculations point towards the factors that lead to high reactivity and excellent enantiocontrol in this reaction.
In recent years, the synthesis of axially chiral compounds has received considerable attention due to their extensive application as biologically active compounds in medicinal chemistry and as chiral ligands in asymmetric catalysis. Chiral phosphoric acids are recognized as efficient organocatalysts for a variety of enantioselective transformations. In this review, we summarize the recent development of chiral phosphoric acid-catalyzed synthesis of a wide range of axially chiral biaryls, heterobiaryls, vinylarenes, N-arylamines, spiranes, and allenes with high efficiency and excellent stereoselectivity.
An enantioselective synthesis of unnatural pyrazole-based α-chiral amino acid derivatives from the asymmetric reaction of N-aryl-5-aminopyrazoles with β,γ-alkynyl-α-imino esters using a chiral spirocyclic phosphoric acid catalyst was developed. Using the established methodology, various pyrazole-based α-amino acid derivatives with tetrasubstituted carbon stereocenters were obtained in 67-98% yields and with 73-99% enantioselectivities. The NH 2 functionality in the corresponding products enables further transformations to a chiral thiourea and a lactam.
We developed a novel asymmetric Friedel–Crafts
alkylation/transamidation
tandem reaction for the enantio- and diastereoselective synthesis
of pyrazolo[3,4-b]pyridin-6-ones bearing a −CF3 unit via synergistic chiral phosphoric acid and MgSO4 catalysis. This [3 + 3] annulation protocol allows the formation
of trifluoromethylated pyrazolo[3,4-b]pyridin-6-ones
with two adjacent tertiary stereocenters in moderate to high yields
(up to 90%), enantioselectivities (up to 97% ee), and diastereoselectivities
(up to >20:1 dr).
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