Enantioselective Friedel–Crafts Reaction of 2-Alkynyphenols with Aromatic Ethers by Chiral Brønsted Acid Catalysis

Abstract

Herein, we report chiral strong Brønsted acid-catalyzed enantioselective Friedel−Crafts reaction of 2-alkynyphenols with aromatic ethers. The reaction affords the corresponding axially chiral styrenes in up to 91% yield and 97% ee.

Divergent Coupling of ortho-Alkynylnaphthols and Benzofurans: [4 + 2] Cycloaddition and Friedel–Crafts Reaction

“…1- (3,. 3f Prepared according to the reaction procedure I above, and the pure product 1d was isolated by flash chromatography column with V PE /V EA ( 50:1) as the eluent; 1 H NMR (500 MHz, CDCl 3 ) δ 8.13 (d, J = 8.7 Hz, 1H), 7.96 (s, 1H), 7.80 (d, J = 8.7 Hz, 1H), 7.77 (d, J = 8.9 Hz, 1H 6-(Benzo [d][1,3] 10 Prepared according to the reaction procedure I above, and the pure product 1e was isolated by flash chromatography column with V PE /V EA (40:1) as the eluent; 1 H NMR (500 MHz, CDCl 3 ) δ 8.08 (d,J = 8.7 Hz,1H),7.86 (s,1H),2H),3H),6.92 (d,J = 7.9 Hz, 1H), 6.08 (s, 1H), 6.02 (s, 2H), 1.47 (s, 9H).…”

“…. 10 Prepared according to the reaction procedure I above, and the pure product 1h was isolated by flash chromatography column with V PE /V EA (80:1) as the eluent; 1 H NMR ( 500 1-(Cyclopropylethynyl)naphthalen-2-ol (1i). 14 Prepared according to the reaction procedure I above, and the pure product 1i was isolated by flash chromatography column with V PE /V EA (80:1) as the eluent; 1 H NMR (500 MHz, CDCl 3 ) δ 8.08 (d,J = 8.4 Hz,1H),7.76 (d,J = 8.2 Hz,1H),7.71 (d,J = 8.8 Hz, 1H), 7.52 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 7.5 Hz, 1H), 7.19 (d, J = 9.0 Hz, 1H), 6.18 (s, 1H), 1.73−1.63 (m, 1H), 1.04−0.93 (m, 4H).…”

“…Recently, we developed a Friedel–Crafts reaction of ortho-alkynylnaphthols with arenes catalyzed by binary acid with Sc­(OTf) 3 and TfOH through the high-energy vinyl carbocations with activated and weakly coordinating trifluoromethanesulfonate anions by Lewis acid Sc­(III) . Very recently, we also reported chiral Brønsted acid-catalyzed Friedel–Crafts reaction of ortho-alkynylnaphthols with indoles and aromatic ethers via the VQM intermediates, respectively. In seeking other heteroaromatic nucleophiles for the reactions with ortho-alkynylnaphthols, we explored benzofurans as potential targets.…”