Recent advances in the metal-catalyzed asymmetric synthesis of chiral allenes

Abstract

Chiral allenes, which are widely existed in natural products, bioactive pharmaceuticals and advanced functional materials, , have received considerable attention in chemistry. They are also identified as versatile building blocks...

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

“…The chemistry of allenes with the intriguing structural architecture of the orthogonal cumulative π-system has been an area of considerable interest over the past few decades. − Allenes work as important building blocks with versatile reactivity and have always been regarded as the hybrids of alkenes and alkynes, which have been engaged in various chemical reactions to access complicated skeletons. A number of efficient transformations of mono- and disubstituted allenes are well developed in modern organic synthesis; however, tri- and tetrasubstituted allenes working as substrates have not always been an easy endeavor and are less developed (Scheme a). , Among them, the carbometalation of allenes with organometallic M–Nu intermediates always resulted in the chemo- and regioselective generation of two disparate carbometalated intermediates M-alkenyl INT (sp 2 -M bond formation) or M-π-allyl INT (sp 3 -M bond formation; Scheme b). − These highly reactive intermediates went through a variety of synthetic transformations and always required rare and expensive noble-metal catalysts, including protonation, annulation, β-hydride elimination, and reductive elimination, providing structurally important organic molecules.…”

Organocatalytic regio- and enantioselective C1-arylation of β,γ-alkynyl-α-imino esters with pyrrolo[2,1-a]isoquinolines

“…2 Accordingly, great advances have been achieved in transition-metal-catalyzed asymmetric synthesis of axially chiral allenes. 3 The past decade has also witnessed a dramatic surge of interest in organocatalytic direct asymmetric synthesis of tetrasubstituted chiral allenes with achiral or racemic precursors, 4 such as allylic alcohol, 5 allenes, 6 enynes 7 or propargylic alcohols (Scheme 1a). 8 Notably, alkynyl ketimines were recognized as useful and versatile building blocks for the preparation of α,α-disubstituted α-amino acids via electrophilic α-addition.…”