Enantioselective Synthesis of Chromanones through Organocatalytic Tandem Reactions

Rapid Construction of Tricyclic Furanobenzodihydropyrans by Asymmetric Tandem Reaction

A process based on the organocatalyzed Mannich/cycloketalization/transesterification tandem reaction of 1-(2-hydroxyaryl)-1,3-diketones and β,γ-alkynyl α-imino esters has been developed, delivering a variety of tricyclic furanobenzodihydropyrans with excellent results (up to 99% yield, 99% ee, and >19:1 dr).

Asymmetric Hydrogenation by Relay Catalysis with FLPs and CPAs: Stereodivergent Synthesis of 3-Substituted Flavanones

To access flavanones bearing two contiguous stereogenic centers, a metal-free asymmetric hydrogenation of racemic 3-alkylidene flavanones has been developed by relay catalysis with achiral FLPs and chiral phosphoric acids, which represents a successful detour for the challenging hydrogenation of 3-substituted flavones. A wide range of trans- and cis-flavanones were obtained in high yields and ≤97% ee.

Access to Chiral Chromenones through Organocatalyzed Mannich/Annulation Sequence

Herein we report an efficient and practical method to access chiral chromenones bearing one α-amino stereogenic center in the β position of the carbonyl group. The quinine-derived squaramide could efficiently promote Mannich/cycloketalization/dehydration tandem reactions between 1-(2-hydroxyaryl)-1,3-diketones and functionalized imines generated in situ, providing a wide range of chiral chromenones with propargylamine or α-amino ester moieties with good results (54 examples, up to 98% ee).

Assembly of fluorinated chromanones via enantioselective tandem reaction

The enantioselective synthesis of fluorinated tricyclic chromanones with multiple vicinal stereogenic centers has been realized for the first time, through the tandem reaction between 2-fluorinated 1-(2-hydroxyaryl)-1,3-diketones and α,β-unsaturated aldehydes. In the presence of chiral amine, the organo-tandem reaction including catalytic Michael addition/cycloketalization/hemiacetalization and acylation sequence provided a wide range of fluorinated tricyclic chromanones with excellent outcomes (>30 examples, up to >99% ee and >19 : 1 d.r.). A plausible catalytic cycle and transition state are also provided for this tandem reaction to rationalize the observed sense of asymmetric induction.