Enantioselective Decarboxylative Alkylation of β-Keto Acids to ortho-Quinone Methides as Reactive Intermediates: Asymmetric Synthesis of 2,4-Diaryl-1-benzopyrans

Abstract

A novel and efficient asymmetric synthesis of 2,4-diaryl-1-benzopyrans via enantioselective decarboxylative alkylation of β-keto acids to o-QM intermediates, followed by sequential cyclization and dehydration, has been developed. The synthetically useful chiral 2,4-diaryl-1-benzopyran derivatives were obtained in moderate to high yields and high enantioselectivities through a one-pot, two-step sequence. This approach offers a facile way to prepare chiral 2,4-diaryl-1-benzopyran derivatives with a wide range of functional group tolerance.

Cooperative Catalysis for the Highly Diastereo‐ and Enantioselective [4+3]‐Cycloannulation of ortho‐Quinone Methides and Carbonyl Ylides

“…[11] In recent years, we and others have meticulously developed Brønsted acid catalyzed reactions of o-QMs with a wide range of typically 2p-nucleophiles, leading to a broad range of benzannulated oxygen heterocycles with good to excellent stereocontrol. [12,13] We now report the first cooperative, catalytic, enantioselective [4+3]-cycloannulation of o-QMs and carbonyl ylides to afford complex and enantiomerically highly enriched oxabicyclic dibenzooxacines. We envisioned that a chiral phosphoric acid would easily form hydrogen-bonded o-QM A starting from ortho-hydroxy benzylalcohol 1 in one catalytic cycle, while in a second and separate catalytic cycle, carbonyl ylide B would be generated through Rh-catalyzed decomposition of a a-diazoester 2 tethered to an aryl ketone (Scheme 1).…”

Diastereoconvergent Dehydrative Nucleophilic Substitutions of Diastereomeric Diarylmethanols with 1,3‐Dicarbonyls Catalyzed by SnBr4

“…When 24 was treated with BBr 3 at –40 °C for 2 h, cleavage of the chiral auxiliary followed by cyclization afforded the pyran 25 in 72 % yield without erosion of optical purity. The absolute configuration of 25 was determined by comparison with a previously reported optical rotation value . In addition, absolute configurations of other alkylated products 12a – 12l , 22 , 23 and 24 were assigned based on the result.…”

Catalytic Asymmetric Syntheses of 2‐Aryl Chromenes

“…In 2018, Kim and coworkers developed a chiral phosphoric acid catalyzed enantioselective decarboxylative alkylation of β‐keto acids to in situ generated ortho ‐quinone methides as reactive intermediates (Scheme ) . Using chiral phosphoric acid 73 as catalyst, the asymmetric alkylation reacted easily between o ‐hydroxy benzylic alcohols 70 and β‐keto acids 71 , followed by sequential cyclization and dehydratioin, provied the corresponding product 4 H ‐chromemes 72 in high yields and enantioselectivities.…”