Organocatalytic synthesis of axially chiral tetrasubstituted allenes

Abstract

Asymmetric organocatalysis is a growing method for the synthesis of axially chiral tetrasubstituted allenes, the most challenging one among allene syntheses. In this method, chiral organocatalysts such as phase-transfer...

Nickel-Catalyzed Enantioconvergent and Diastereoselective Allenylation of Alkyl Electrophiles: Simultaneous Control of Central and Axial Chirality

“…Chiral allenes are of substantial interest, as they are found in natural products and have utility in wide-ranging fields such as asymmetric catalysis, medicinal chemistry, , and materials science; consequently, considerable attention has been focused on the development of methods for their synthesis. − We envisioned a new approach to the synthesis of enantioenriched allenes, through a metal-catalyzed coupling of an alkyl halide with a 1,3-enyne in the presence of a hydride reagent (Figure C) …”

Challenging Task of Ni-Catalyzed Highly Regio-/Enantioselective Semihydrogenation of Racemic Tetrasubstituted Allenes via a Kinetic Resolution Process

“…On the other hand, considering the intriguing peculiarities of these two cumulated CC bonds and the special axial chirality, the optically active allenes are not only abundant in plenty of natural products, biologically active compounds, and functional materials but also proven as versatile synthetic precursors for the preparation of other important molecules. − In addition, tetrasubstituted axially chiral allenes worked as privileged chiral ligands and organocatalysts in asymmetric catalytic synthesis. , As a consequence, great efforts have been made toward the development of asymmetric catalytic tactics involving a single or two electron transfer process − to access these valuable axially enantioenriched allenes. At present, some catalytic enantioselective synthesis processes have been developed, such as asymmetric 1, n -addition to conjugated enynes and derivatives, − asymmetric cascade reactions, − asymmetric alleno-Mannich-type reaction, enantioselective radical reactions with alkynes, , asymmetric multicomponent reaction, organocatalytic asymmetric C­(sp 2 )–H allylic alkylation of racemic trisubstituted allenoates, Pd-catalyzed decarboxylative γ-arylation of acyclic β,γ-alkynoic acids, and asymmetric transformations with propargylic alcohols. − Despite these noticeable recent advances, the direct asymmetric transformations of racemic tetrasubstituted allenes to construct axially chiral tetrasubstituted allenes are still not well-established and are of great interest.…”

Palladium-Catalyzed Allylic Alkylation Reactions of Nucleophilic Allenones: Asymmetric Allylic Alkylation, Z/E Divergent Allylic Alkylation, and [5 + 2] Annulation

“…This research topic has been greatly expanded during the past two decades, and diverse elegant strategies have been established for the efficient synthesis of allenes. Among them, strategies via catalytic functionalization of achiral or racemic substrates for direct construction of functionalized allenes in both enantio- and nonenantioselective patterns have drawn particular interest. − In this context, the research group of Ma is listed as one of the main contributors. Various enantioselective catalytic protocols such as β-elimination, allenylic and propargylic substitution, Heck reaction, Suzuki coupling, alkynyl ketimine addition, and allenylation of alkynes with aldehydes have been developed by the group, allowing convenient synthesis of structurally diverse functionalized allenes .…”