Rapid Construction of Tricyclic Furanobenzodihydropyrans by Asymmetric Tandem Reaction

Abstract

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).

Accessing unnatural α-amino acids with tetrasubstituted stereogenic centersviacatalytic enantioselective reactions of ketimine-type α-iminoesters/α-iminoamides

“…In 2023, Zhang, Duan, Wang, and co-workers also used acyclic ketimine-type α-iminoesters 47a in enantioselective direct Mannich-type reactions with 1-(2-hydroxyaryl)-1,3-diketones in the presence of quinine-derived bifunctional squaramide 23c (Scheme 22). 40 This chemistry provided tricyclic furanobenzodihydropyrans 59 , which are valuable skeletons for constructing various natural products and functional materials, via direct-Mannich, cycloketalization, and transesterification chemistry in a one-pot manner.…”

Strategies and Methods for the Catalytic Asymmetric Synthesis of Benzofuran/Benzopyran Fused Acetals: A Review

“…[46] Very recently, our group developed an organocatalyzed Mannich/cycloketalization/transesterification tandem reaction of 1-(2-hydroxyaryl)-1,3-diketones 55 and β,γ-alkynyl α-imino esters 56 for the synthesis of highly functionalized furanobenzodihydropyrans 57 (Scheme 27). [47] To speculate the possible stereoselective control of this tandem reaction, a reasonable activated mode was proposed. As shown in Scheme 27, the N-Boc group will make the α-imino ester easily activated by organocatalyst Cat.6 via hydrogen-bonding interactions, allowing it to readily undergo asymmetric Mannich reaction with activated 1,3-diketone.…”

“…Very recently, our group developed an organocatalyzed Mannich/cycloketalization/transesterification tandem reaction of 1‐(2‐hydroxyaryl)‐1,3‐diketones 55 and β,γ‐alkynyl α‐imino esters 56 for the synthesis of highly functionalized furanobenzodihydropyrans 57 (Scheme 27). [47] …”