Enantioselective [3 + 2] Formal Cycloaddition of 1-Styrylnaphthols with Quinones Catalyzed by a Chiral Phosphoric Acid

Abstract

The first highly enantioselective [3 + 2] formal cycloaddition of 1-styrylnaphthols (or phenol) with quinones catalyzed by a chiral phosphoric acid has been reported. A class of trans-2,3-diarylbenzofurans were prepared efficiently (up to 99% yield, >20:1 dr, 99% ee). This organocatalytic procedure allows lowering of the catalyst loading to 0.5 mol % without considerable loss in reactivity and enantioselectivity.

Conversion of two stereocenters to one or two chiral axes: atroposelective synthesis of 2,3-diarylbenzoindoles

“…Inspired by the abovementioned elegant studies on central-to-axial chirality conversion and our previous study on the asymmetric [3 + 2] formal cycloaddition reaction,23 we envisioned that an enantioselective [3 + 2] annulation of 1-styrylnaphthols with azonaphthalenes followed by oxidative aromatization would generate benzoindole (C(2) position) naphthyl atropisomers. To achieve this goal, we needed to address the following issues: (1) accomplishment of a highly diastereoselective and enantioselective [3 + 2] annulation; (2) installation of suitable groups around the C–C axis to avoid free rotation; and (3) realization of efficient chirality conversion with enantioselective and diastereoselective control via the development of mild oxidation conditions.…”

Asymmetric Synthesis of Enantioenriched 2‐Aryl‐2,3‐Dihydrobenzofurans by a Lewis Acid Catalyzed Cyclopropanation/Intramolecular Rearrangement Sequence

“…Chiral 2‐aryl‐2,3‐dihydrobenzofuran derivatives form the structural skeletons of numerous naturally occurring biologically active compounds, such as (+)‐lithospermic acid and callislignan A (Figure ). As a consequence of the importance of the structural core, considerable attention has been devoted in the past few decades to the development of catalytic stereoselective methods for the synthesis of highly functionalized 2‐aryl‐2,3‐dihydrobenzofuran derivatives . Representative approaches toward these scaffolds include asymmetric hydrogenation, C−H insertion reactions, oxidative dimerization, [3+2] cycloaddition reactions, and others .…”

“…As a consequence of the importance of the structural core, considerable attention has been devoted in the past few decades to the development of catalytic stereoselective methods for the synthesis of highly functionalized 2‐aryl‐2,3‐dihydrobenzofuran derivatives . Representative approaches toward these scaffolds include asymmetric hydrogenation, C−H insertion reactions, oxidative dimerization, [3+2] cycloaddition reactions, and others . Of these, catalytic enantioselective intramolecular C−H insertion reactions utilizing metal carbenoid intermediates from diazo compounds have been studied extensively –.…”

Asymmetric Synthesis of Triaryl‐Substituted Chromans with Multiple Stereogenic Centers by [4+2] Cycloaddition Reaction

“…Recently, Zhou's group reported a CPA catalyzed [3+2] cycloaddition of 1,4‐quinones with 1‐styrylnaphthols ( O ‐vinylphenols) to obtain benzofuran structures (Scheme ) . Because ortho hydroxy group could attach to chiral catalysts closely by the formation of hydrogen bond, o‐vinylphenols underwent many asymmetric transformations as nucleophile or electrophile reagents and corresponding products were obtained with excellent enantioselectivities .…”