Enantioselective Synthesis of Pyrrolizin-1-ones via Lewis Base Catalyzed N-Allylation of N-Silyl Pyrrole Latent Nucleophiles

Enantioselective Lewis base catalysed allylation of picoline- and quinaldine-based latent pronucleophiles

Picolines and quinaldines are valuable building blocks and intermediates in the synthesis of natural products and pharmaceuticals. Functionalization of the methyl group in picolines and quinaldines under mild conditions is challenging. We report that the concept of latent pronucleophiles enables Lewis base catalysed allylation of picolines and quinaldines with allylic fluorides starting from silylated picolines and quinaldines. Reactions afford enantioenriched allylation products when chiral Lewis base catalysts are used. The allylation products can be rapidly transformed to quinolizine-4-ones.

Regioconvergent Nucleophilic Substitutions with Morita-Baylis-Hillman Fluorides

Lithium iodide enables regioconvergent C-F bond functionalization of isomeric Morita-Baylis-Hillman fluorides with carbon, sulfur, and nitrogen nucleophiles. The defluorinative carbon-carbon and carbon-heteroatom bond formations give multifunctional compounds in excellent yields and with good to high diastereoselectivities at room temperature. The possibility of catalytic enantioselective allylation is also discussed.

Regioselectivity Switch of α-Amino Acid-Derived Esters and MBH Carbonates for the Synthesis of Allyl-Substituted Azlactones

Allylic azlactones are greatly significant in terms of potential bioactivities and synthetic applications. Owing to the burgeoning interest of the pharmaceutical industry in α-amino acid derivatives, discovering strategies for the synthesis of allylic azlactones is important. Herein, we establish a transition-metal-free regioselectivity switch of α-amino acid-derived esters and MBH carbonates, which exhibits broad reaction scope and good reaction yields. Control reactions indicate that both base and solvent are important for regioselectivity.

Synthesis of β-Amino Acid Derivatives via Enantioselective Lewis Base Catalyzed N-Allylation of Halogenated Amides with Morita-Baylis-Hillman Carbonates

Trifluoro- and trichloroacetamides serving as pronucleophiles undergo enantioselective Lewis base catalyzed N-allylation with Morita-Baylis-Hillman carbonates to produce enantioenriched β-amino acid derivatives. The reactions proceed as a kinetic resolution to give the allylation products and the remaining carbonates in good yields and high enantioselectivity. The obtained products are amenable to diastereoselective derivatization to produce a library of spiro-isoxazoline lactams.

Lewis-Base-Catalyzed N-Allylation of Silyl Carbamate Latent Pronucleophiles with Allylic Fluorides

Silyl carbamates, latent pronucleophile surrogates of carbamates, undergo allylation using allylic fluorides in the presence of common Lewis base catalysts. The reactions are rendered enantioselective in the presence of chiral Lewis base catalysts and produce suitably protected derivatives of enantioenriched chiral β-amino acids. The design of the latent pronucleophile featuring both a silyl group and an electron-deficient carbamate is instrumental in lowering the nucleophilicity of nitrogen and enabling enantioselective allylation in the presence of chiral cinchona alkaloid-based catalysts.

3-Nitroindoles Serving as N-Centered Nucleophiles for Aza-1,6-Michael Addition to para-Quinone Methides

An unprecedented N-alkylation of 3-nitroindoles with para-quinone methides was developed for the first time. Using potassium carbonate as the base, a wide range of structurally diverse N-diarylmethylindole derivatives were obtained with moderated to good yields via the protection group migration/aza-1,6-Michael addition sequences. The reaction process was also demonstrated by control experiments. Different from the previous advances where 3-nitrodoles served as electrophiles trapping by various nucleophiles, the reaction herein is featured that 3-nitrodoles is defined with latent N-centered nucleophiles to react with ortho-hydrophenyl p-QMs for construction of various N-diarylmethylindoles.

Catalytic asymmetric defluorinative allylation of silyl enol ethers

The stereocontrolled installation of alkyl fragments at the alpha position of ketones is a fundamental yet unresolved transformation in organic chemistry. Herein we report a new catalytic methodology able to construct α-allyl ketones via defluorinative allylation of silyl enol ethers in a regio-, diastereo- and enantioselective manner. The protocol leverages the unique features of the fluorine atom to simultaneously act as a leaving group and to activate the fluorophilic nucleophile via a Si-F interaction. A series of spectroscopic, electroanalytic and kinetic experiments demonstrate the crucial interplay of the Si-F interaction for successful reactivity and selectivity. The generality of the transformation is demonstrated by synthesising a wide set of structurally diverse α-allylated ketones bearing two contiguous stereocenters. Remarkably, the catalytic protocol is amenable for the allylation of biologically significant natural products.

Recent Advances in Lewis Base-Catalysed Chemo-, Diastereo- and Enantiodivergent Reactions of Electron-deficient Olefins and Alkynes

Lewis base catalysis provides powerful synthetic strategies for the selective construction of carbon-carbon and carbon-heteroatom bonds. Thus continuous efforts have been deployed to develop effective methodologies involving Lewis base catalysis. The nucleophilicity and steric hindrance of Lewis base catalyst often plays a major role in catalytic reactivity and selectivity in the reaction. In the past decades, tremendous progress has been made in the divergent construction of valuable motifs under Lewis base catalysis. In this review, we provide a comprehensive and updated summary of Lewis base-catalysed chemo-, diastereo- and enantiodivergent reaction, as well as the related mechanism will be highlighted in detail.

Enantioselective synthesis of polycyclic pyrrole derivatives by iridium-catalyzed asymmetric allylic dearomatization and ring-expansive migration reactions

Herein, we report an N-alkylation of pyrroles triggered by an unprecedented selective ring-expansive migration of the spiro-2H-pyrrole intermediates obtained via Ir-catalyzed asymmetric allylic dearomatization. The reaction affords a series of tetrahydropyrrolo[1,2-c]pyrimidine derivatives in good yields (up to 88%) with excellent enantioselectivity (up to >99% ee). The proposed reaction mechanism is supported by DFT calculations and the characterization of the key intermediate.

Synthesis of Chiral gem-Difluoromethylene Compounds by Enantioselective Ethoxycarbonyldifluoromethylation of MBH Fluorides via Silicon-Assisted C-F Bond Activation

The enantioselective ethoxycarbonyldifluoromethylation of Morita-Baylis-Hillman (MBH) fluorides with Me₃SiCF₂CO₂Et under organocatalysis is described. Moderately functionalized chiral gem-difluoromethylene compounds with a stereogenic "C-CF₂-C*" unit were synthesized in high yields with high enantioselectivities. The initial C-F bond activation is assisted by the silicon atom via a dual S_N2'-S_N2' stepwise pathway. Dynamic kinetic resolution of the MBH-fluorides explained the high yields and high ee's of the products. The method was extended to the enantioselective introduction of "Het-CF₂" units.

Enantioselective Lewis base catalyzed phosphonyldifluoromethylation of allylic fluorides using a C-silyl latent pronucleophile

The first enantioselective phosphonyldifluoromethylation is enabled by the use of a latent silylated C-centered pronucleophile in the Lewis base catalyzed substitution of allylic fluorides.