Organocatalytic synthesis of chiral tetrasubstituted allenes from racemic propargylic alcohols

Abstract

Although chiral allene preparation via formal SN2’ nucleophilic substitutions of enantioenriched propargylic derivatives or metal-catalyzed reactions of racemic propargylic derivatives has attracted considerable attention and found applications in many areas of research, direct use of propargylic alcohols instead of propargylic derivatives for catalytic asymmetric allene synthesis is unknown. Here, we show that a highly enantioselective synthesis of tetrasubstituted allenes from racemic propargylic alcohols has been realized by organocatalysis with good efficiency (up to 96% yield and 97% ee). The intermolecular C–C and C–S bond formation was achieved efficiently with simultaneous stereocontrol over the axial chirality. Furthermore, an adjacent quaternary stereocenter could also be constructed. Mechanistically, the reaction may involve efficient stereocontrol on the propargylic cation by its chiral counter anion or 1,8-conjugate addition of para-quinone methides. In sharp contrast to previous central chirality construction, this process employs quinone methides for axial chirality construction.

Competition of Pairing and Nematicity in the Two-Dimensional Electron Gas

“…Anisotropy was also detected in microwave pinning resonance [92] and surface acoustic wave propagation [93,94]. Since experiments typically detect broken rotational symmetry, we still lack information on translational order in these phases [95]. Therefore anisotropic phases at ν = 9/2, 11/2, 13/2, ... are referred to as the QHN, or simply the nematic [96].…”

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

“…As a further expansion of their work, Sun and co‐workers applied the CPA‐catalyzed reactions of p ‐QMs to the enantioselective synthesis of tetrasubstituted allenes (Scheme ) . Two chiral Brønsted acid catalysts, C6 and C7 , not only allowed the in situ generation of the reactive intermediates, thereby simplifying substrate preparation and expanding functional‐group compatibility, but also ensured the activation of both partners and excellent remote stereocontrol.…”

Palladium‐Catalyzed Decarboxylative γ‐Arylation for the Synthesis of Tetrasubstituted Chiral Allenes

“…[5g,h, 10] Some selected examples along these lines are listed herein:I n2 013, Maruoka and coworkers described the asymmetric functionalization of estersubstituted allenes in adeprotonation/alkylation sequence by phase-transfer catalysis (Scheme 1b). [12] Recently,Aggarwal and co-workers presented an enantiodivergent method to access highly substituted allenes,i ncluding tetrasubstituted allenes,b yp oint-to-axial chirality transfer with chiral allyl boronic esters as substrates. [12] Recently,Aggarwal and co-workers presented an enantiodivergent method to access highly substituted allenes,i ncluding tetrasubstituted allenes,b yp oint-to-axial chirality transfer with chiral allyl boronic esters as substrates.…”