Copper‐Catalyzed Enantioselective 1,6‐Boration of para‐Quinone Methides and Efficient Transformation of gem‐Diarylmethine Boronates to Triarylmethanes

Abstract

Presented is the first enantioselective copper-catalyzed 1,6-conjugate addition of bis(pinacolato)diboron to para-quinone methides. The reaction proceeds with excellent yields and good to excellent enantioselectivities, and provides an attractive approach to the construction of optically active gem-diarylmehtine boronic esters. Additionally, the subsequent conversion of the derived potassium trifluoroborates into triarylmethanes with highly enantiospecificity was realized.

Recent Advances in the Catalytic Enantioselective Reactions of para‐Quinone Methides

“…In 2015, Liao and co‐workers described the first enantioselective copper‐catalyzed 1,6‐conjugate addition of bis(pinacolato)diboron to p ‐QMs (Scheme ) . Catalyzed by a combination of CuCl and ligand L1 , bis(pinacolato)diboron, [B 2 (pin) 2 ], reacted smoothly with p ‐QMs 75 to afford gem ‐diarylmethine boronates in 71–98 % yield with 66–97 % ee .…”

“…In 2015, Liao and co-workers described the first enantioselective copper-catalyzed 1,6-conjugate addition of bis(pinacolato)diboron to p-QMs( Scheme 24). [29] Catalyzed by ac ombination of CuCl and ligand L1,b is(pinacolato)diboron,[ B 2 (pin) 2 ], reacted smoothly with p-QMs 75 to afford gem-diarylmethine boronates in 71-98% yield with 66-97 % ee. The enantioselectivity originated from the approach of the planar p-QM to the si face of the (SOP)Cu/Bpin speciest oa void steric interactions between the phenylr ing of the p-QM and the tert-butyl sulfinyl group of ligand L1.T he transformation of gem-diarylmethine boronates into enantioenriched triarylmethanes was also documented.…”

Enantioselective Synthesis of Triarylmethanes via Organocatalytic 1,6‐Addition of Arylboronic Acids to para‐Quinone Methides

“…Moreover, thiophenyl-substituted triarylmethanes were reported to be antitubercular agents. [2g] Despite remarkable progress in the synthesis of racemic triarylmethanes, [1,3] the asymmetric versions towards chiral triarylmethanes remain rare [4][5][6][7] prob-ably due to the difficulty in finding a suitable catalytic system to stereoselectively install three similar aryl groups at the same position. [2g] Despite remarkable progress in the synthesis of racemic triarylmethanes, [1,3] the asymmetric versions towards chiral triarylmethanes remain rare [4][5][6][7] prob-ably due to the difficulty in finding a suitable catalytic system to stereoselectively install three similar aryl groups at the same position.…”

“…[2f] A natural product selaginpulvilins A exhibited remarkable inhibitory activity against phosphodiesterase-4 (PDE4), a drug target for the treatment of asthma and chronic obstructive pulmonary disease. [2g] Despite remarkable progress in the synthesis of racemic triarylmethanes, [1,3] the asymmetric versions towards chiral triarylmethanes remain rare [4][5][6][7] prob-ably due to the difficulty in finding a suitable catalytic system to stereoselectively install three similar aryl groups at the same position. Four asymmetric synthetic strategies available are (Scheme 1a): i) stereospecific cross-coupling reactions of enantioenriched starting compounds; ii) asymmetric CÀH functionalization reactions; iii) transition metal-catalyzed asymmetric aryl addition; iv) asymmetric Friedel-Crafts alkylation of electron-rich arenes (indoles and naphthanols).…”

Switchable Synthesis of Z‐Homoallylic Boronates and E‐Allylic Boronates by Enantioselective Copper‐Catalyzed 1,6‐Boration

“…[1][2][3] One important route to these compounds is the catalyticenantioselective boration of electron-deficienta lkenes. [8,9] Aside from promoting 1,6-boration over competing 1,4-boration, the 1,6boration of electron-deficient conjugatedd ienes has the potential to give four products which differ in the positiona nd/ or the E/Z geometry of the remaining alkene (Scheme 1). [8,9] Aside from promoting 1,6-boration over competing 1,4-boration, the 1,6boration of electron-deficient conjugatedd ienes has the potential to give four products which differ in the positiona nd/ or the E/Z geometry of the remaining alkene (Scheme 1).…”