Z-Retentive Asymmetric Allylic Substitution Reactions of Aldimine Esters under Ru/Cu Dual Catalysis

Catalyzed Asymmetric Michael Additions of 1-Pyrroline Esters with β-Fluoroalkyl Alkenyl Imides and Azodicarboxylates

The asymmetric Michael addition reactions of 1-pyrroline esters with β-fluoroalkyl alkenyl imides and dialkyl azodicarboxylates catalyzed by the AgOAc/Ph-phosferrox or CuOAc/(R)-BINAP complex have been developed. A series of chiral 1,5,5-trisubstituted pyrroline ester derivatives have been obtained in 53%-90% yields with 80%-99% ee's and all > 20:1 dr. The gram-scale synthesis and synthetic application of the chiral trifluoromethylated 1-pyrroline adducts were exhibited: the pyrrolizidin-3-one analogue was first synthesized with 94% ee and > 20:1 dr through two steps of hydrolysis and reductive cyclization; the pyrrolidine and lactam derivatives were also successfully provided under the reducing conditions of NaBH3CN and Pd/C─H2, respectively.

Iridium-Catalyzed Asymmetric Allylic Alkylation of Boron Enolates to Construct Acyclic All-Carbon Quaternary Stereocenters

Enolates are ubiquitous intermediates in organic synthesis. Among them, boron enolates exhibit distinctive reactivity patterns and selectivities due to the presence of a boron atom, making their synthesis highly attractive. Although methods for accessing ketone- or ester-derived boron enolates are well-developed, much less progress has been made in the development of aldehyde-derived boron enolates due to aldehydes' high tendency toward self-condensation. Therefore, the practical applications of aldehyde-derived boron enolates are significantly hindered. We present herein an efficient method for the preparation of aldehyde-derived boron enolates via the 1,2-hydroboration of ketenes with boranes, avoiding the use of acidic R2BCl/R2BOTf and bases and leading to improved functional group tolerance. Utilizing this convenient protocol, we developed an Ir-catalyzed asymmetric allylic alkylation of boron enolates, yielding a wide array of chiral aldehydes bearing acyclic all-carbon quaternary centers with high chemo-, regio-, and enantioselectivity, which are prevalent in various natural products and bioactive molecules. The synthetic utility and practicality of this method are demonstrated through gram-scale reactions and asymmetric syntheses of the ent-5HT1 A antagonist as well as biological activity studies in inhibiting the growth of plant pathogens.

Enantioselective Three-Component α-Allylic Alkylation of α-Amino Esters by Synergistic Photoinduced Pd/Carbonyl Catalysis

Photoinduced excited-state Pd catalysis has emerged as an intriguing strategy for unlocking new reactivity potential of simple substrates. However, the related transformations are still limited and the enantiocontrol remains challenging. Organocatalysis displays unique capability in substrate activation and stereocontrol. Combination of organocatalysis and photoinduced excited-state Pd catalysis may provide opportunities to develop new enantioselective reactions from simple substrates. By applying cooperative triple catalysis including excited-state Pd catalysis, ground-state Pd catalysis, and carbonyl catalysis, we have successfully realized enantioselective α-allylic alkylation of α-amino esters with simple styrene and alkyl halide starting materials. The reaction allows rapid modular assembly of the three reaction partners into a variety of chiral quaternary α-amino esters in good yields with 90-99 % ee, without protecting group manipulations at the active NH2 group. The cooperation of the chiral pyridoxal catalyst and the chiral phosphine ligand accounts for the excellent chirality induction.

Interrupting Associative π-σ-π Isomerization Enables Z-Retentive Asymmetric Tsuji-Trost Reaction

The asymmetric Tsuji-Trost reaction has been extensively studied due to its importance in establishing stereogenic centers, often adjacent to an E-olefin moiety in organic molecules. The generally preferential formation of chiral E-olefin products is believed to result from the thermodynamically more stable syn-π-allylpalladium intermediate. The rapid associative π-σ-π isomerization makes it challenging to synthesize chiral Z-olefin products via the transient anti-π-allylpalladium intermediate. Herein, we report a strategy for regulating associative π-σ-π isomerization by tuning the steric bulkiness of the ligands, allylic leaving groups, and counteranions. The utilization of a Pd catalyst derived from chiral phosphoramidite ligands interrupts the associative π-σ-π isomerization, enabling a highly efficient Z-retentive asymmetric Tsuji-Trost reaction toward an array of α-amino acid derivatives bearing a Z-olefin motif in high yields (up to 95%) and excellent stereoselectivity (up to 99% ee and >19:1 Z/E) with low catalyst loading (0.1 mol %). The mechanistic insights and the design strategy reported in this work pave the way for rational developments of Z-retentive asymmetric Tsuji-Trost-type reactions.

Rhodium-Catalyzed Synthesis of Trifluoromethyl-Containing Allylic Alcohols Via Z-Alkenyl Transfer with High Stereochemistry Retention

Herein, we report the rhodium-catalyzed Z-alkenyl transfer from tertiary allylic alcohols to aryl trifluoromethyl ketones, which provided an efficient way of preparation of trifluoromethyl-containing Z-allylic alcohols via β-Z-alkenyl elimination. The key Z-alkenyl-rhodium species were generated with a high degree of stereochemical retention. This reaction featured a broad substrate scope and good functional tolerance and would offer a fascinating approach for the synthesis of Z-alkenes.

Enantioselective Formal 1,2-Diamination of Ketenes with Iminosulfinamides: Asymmetric Synthesis of Unnatural α,α-Disubstituted α-Amino Acid Derivatives

A method was developed for the enantioselective formal 1,2-diamination of disubstituted ketenes using iminosulfinamides as nitrogen sources. The protocol involves the addition of lithium iminosulfinamides to ketenes to form N-iminosulfinyl amide metalloenolates. These metalloenolates then undergo a [2,3]-sigmatropic rearrangement to yield unnatural α,α-disubstituted α-amino acid derivatives with high enantiopurity. The chirality present at the sulfur atom in the iminosulfinamides is effectively transferred to α carbon of the resulting products, facilitating the highly enantioselective amination of ketenes.