Yirong Zhou

Synthesis of C1-symmetric chiral secondary diamines and their applications in the asymmetric copper(II)-catalyzed Henry (nitroaldol) reactions.

A small library of C(1)-symmetric chiral diamines (L1-L9) was constructed via condensing exo-(-)-bornylamine or (+)-(1S,2S,5R)-menthylamine with various Cbz-protected amino acids. Among them, ligand L1/CuCl(2)·2H(2)O complex (2.5 mol %) shows outstanding catalytic efficiency for Henry reaction between a variety of aldehydes and nitroalkanes to afford the expected products in high yields (up to 98%) with excellent enantioselectivities (up to 99%) and moderate to good diastereoselectivities (up to 90:10). This process is air- and moisture tolerant and has been applied to the synthesis of (S)-2-amino-1-(3,4-dimethoxyphenyl)ethanol (9), a key intermediate for (S)-epinephrine and (S)-norepinephrine. On the basis of HRMS and X-ray diffraction analysis of the L1/CuCl(2) complex, a transition-state model was proposed to explain the origin of asymmetric induction. The low catalyst loading, excellent yields and enantioselectivities, inexpensive copper salt, and mild reaction conditions make our catalytic system to be practically useful.

Copper(II)-Catalyzed Asymmetric Henry Reaction of o-Alkynylbenzaldehydes Followed by Gold(I)-Mediated Cycloisomerization: An Enantioselective Route to Chiral 1H-Isochromenes and 1,3-Dihydroisobenzofurans

By combining the copper(II)-catalyzed asymmetric Henry reaction of o-alkynylbenzaldehydes with subsequent gold(I)-catalyzed cycloisomerization, optically active 1H-isochromenes and 1,3-dihydroisobenzofurans were successfully synthesized in good overall yields with good to excellent enantioselectivities (up to 98%). Various substrates were investigated, and a correlation between the regioselectivity and electronic nature of the substrates was studied. The substrates with electro-donating groups at the alkynyl moiety preferred a 6-endo-dig manner to generated 1H-isochromenes 3 as main products (up to >30:1) while the ones with electron-withdrawing groups were inclined to undergo 5-exo-dig cyclization to form 1,3-dihydroisobenzofurans 4 (up to 1:5).

Directing‐Group‐Assisted Transition‐Metal‐Catalyzed Direct Intermolecular C−H Amidation and Amination of Arenes

This review focuses on the most recent advances in the field of transition‐metal‐catalyzed direct intermolecular C−H amidation and amination of arenes. The manuscript is divided into two parts according to whether or not external oxidants are required. The first part includes the cases of simple neutral amines, amides, or sulfonamides in combination with external oxidants. The second section contains the examples of preactivated amino sources in the absence of any external oxidants. In each part, the content is classified in line with the different types of transition‐metal catalysts used, including Rh, Ru, Ir, Pd, Cu, Ni, Co, and Fe. In addition, the substrate scope and limitations as well as catalytic mechanism are discussed.

Camphor-derived C1-symmetric chiral diamine organocatalysts for asymmetric Michael addition of nitroalkanes to enones.

A series of stable C(1)-symmetric chiral diamines (2a–2l) were conveniently synthesized by condensing exo-(-)-bornylamine or (+)-(1S,2S,5R)-menthylamine with various commercially available Cbz-protected amino acids. Among them, 2a can efficiently promote the Michael addition of nitroalkanes to a broad scope of enones with high yields (up to 96%) and excellent enantioselectivities (up to 98%) under mild conditions.

Merging Asymmetric Henry Reaction with Organocatalytic Cascade Reaction for the Construction of a Chiral Indolizidine Alkaloid Skeleton

A sequential reaction combining the copper-catalyzed asymmetric Henry reaction with the organocatalytic Michael addition-hemiacetalization cascade reaction was developed. The C1-symmetric chiral diamine L1-copper complex was responsible for the first highly enantioselective Henry reaction, while diphenylprolinol silyl ether A acted as effective organocatalyst for the second cascade reaction between chiral β-nitro alcohol and α,β-unsaturated aldehydes. Via rational design and combination of the two independent catalytic systems, good yields and excellent enantioselectivities and diastereoselectivities were achieved for a broad substrate scope under mild reaction conditions. The synthetic utility of this sequential catalytic asymmetric cascade reaction was demonstrated as an alternative and straightforward stereoselective synthesis strategy for chiral indolizidine alkaloid and its analogues.

Organocatalytic Asymmetric Reduction of Fluorinated Alkynyl Ketimines

Highly chemoselective catalytic transfer hydrogenation of fluorinated alkynyl ketimines has been achieved by employing chiral phosphoric acid as a catalyst with benzothiazoline as a hydride source, providing the corresponding chiral fluorinated propargylamines in good yields and excellent enantioselectivities. In addition, iodocyclization of fluorinated propargylamine affords chiral 3-iodo-2-(trifluoromethyl)-1,2-dihydroquinoline, which can be easily converted to 2-(trifluoromethyl)- 1,2-dihydroquinoline derivatives with the selective COX-2 inhibitory activity.