Lewis Base Catalyzed Mannich-Type Reactions between Trimethylsilyl Enol Ethers and Aldimines

Iridium-Catalyzed Amidation of In Situ Prepared Silyl Ketene Acetals to Access α-Amino Esters

Disclosed herein is a convenient Ir-catalyzed amidation of esters to access α-amido esters. Initially prepared silyl ketene acetals are directly employed, without separate purification, for subsequent amidation with an oxycarbonylnitrenoid precursor using the Cp*(LX)Ir(III) catalyst. The α-amidation was facile for both α-aryl and α-alkyl esters. Density functional theory studies revealed that the generation of a putative Ir-nitrenoid is facilitated by the chelation of the countercation additive during the N-O bond cleavage of the nitrene precursor.

Nucleophilic Activation of Hydrosilanes via a Strain-Imposing Strategy Leading to Functional Sila-aromatics

Carefully designed cyclic hydrosilanes enable trans-selective hydrosilylation of unactivated alkynes without transition metal catalysts via silicate formation. Employment of sterically demanding bidentate ligands of silicon increases steric congestion upon silicate formation, and this strain-imposing strategy facilitates hydride transfer. This hydrosilylation provides efficient access to diverse benzosiloles, silaphenalenes, and related silacycles.

Straightforward Access to Anthrone Functionalized Benzylic Amines via Organocatalytic 1,2-Addition of Anthrones to Imines at Ambient Temperature

Activation of anthrone via benzylic deprotonation in the presence of triethylamine paves the way for the 1,2-addition reaction with imines to provide the desired functionalized anthrones in good to excellent yields under mild and operationally simple reaction conditions with a broad range of substrate scopes without using any external additives or toxic stoichiometric reagents.

Main Group Metal-Mediated Transformations of Imines

Main-group-metal-mediated transformations of imines have earned a valued place in the synthetic chemist's toolbox. Their versatility allows the simple preparation of various nitrogen containing compounds. This review will outline the early discoveries including metallation, addition/cyclisation and metathesis pathways, followed by the modern-day use of imines in synthetic methodology. Recent advances in imine C-F activation protocols are discussed, alongside revisiting "classic" imine reactivity from a sustainable perspective. Developments in catalytic methods for hydroelementation of imines have been reviewed, highlighting the importance of s-block metals in the catalytic arena. Whilst stoichiometric transformations in alternative reaction media such as deep eutectic solvents or water have been summarised. The incorporation of imines into flow chemistry has received recent attention and is summarised within.

Design of bifunctional chiral phenanthroline ligand with Lewis basic site for palladium-catalyzed asymmetric allylic substitution

Conceptually new bifunctional chiral ligands with Lewis basic site were developed for Pd-catalyzed asymmetric allylic substitution.

Direct synthesis of N-sulfinyl- and N-sulfonylimines via copper/l-proline-catalyzed aerobic oxidative cascade reaction of alcohols with sulfinamides or sulfonamides

An efficient one-pot synthesis of N-sulfinyl- and N-sulfonylimines directly from alcohols with sulfinamides or sulfonamides.

Stereoselective ZrCl4-Catalyzed Mannich-type Reaction of β-Keto Esters with Chiral Trifluoromethyl Aldimines

A method for the synthesis of fluorinated β'-amino β-dicarbonyl compounds using a Zr-catalyzed Mannich-type reaction has been developed, starting from N-protected trifluoromethyl aldimines and cyclic or acyclic β-keto esters bearing different ester residues. The in situ generated metallic complex reacted with optically pure trifluoromethyl aldimine derived from (R)-α-methylbenzylamine, giving a highly diastereoselective asymmetric Mannich-type addition with formation of a chiral quaternary center. The absolute configuration at the new chiral centers was assigned through two-dimensional nuclear Overhauser effect spectroscopic analysis coupled with computational studies.

B(C6F5)3-Catalyzed Group Transfer Polymerization of n-Butyl Acrylate with Hydrosilane through In Situ Formation of Initiator by 1,4-Hydrosilylation of n-Butyl Acrylate

The group transfer polymerization (GTP) of n-butyl acrylate (nBA) using hydrosilane (R₃SiH) and tris(pentafluorophenyl)borane (B(C₆F₅)₃) has been studied, which did not need to use the initiator of a silyl ketene acetal (SKA) as the starting polymerization component. B(C₆F₅)₃ catalyzed the in situ 1,4-hydrosilylation of nBA by R₃SiH to generate the corresponding SKA prior to the polymerization of nBA, which was confirmed by the ¹H NMR measurement of the model reaction. The formed SKA performed as the initiator for the B(C₆F₅)₃-catalyzed GTP of nBA leading to well-defined polymers with targeted molar masses and low dispersities.

Polymer-supported PPh3 as a reusable organocatalyst for the Mukaiyama aldol and Mannich reaction

Polystyrene-supported PPh₃ (PS-PPh₃) catalyzes the aldol reaction of aldehydes and imines to give the corresponding products in good to high yields.

Lewis base catalysis of the Mukaiyama directed aldol reaction: 40 years of inspiration and advances

Since the landmark publications of the first directed aldol addition reaction in 1973, the site, diastereo-, and enantioselective aldol reaction has been elevated to the rarefied status of being both a named and a strategy-level reaction (the Mukaiyama directed aldol reaction). The importance of this reaction in the stereoselective synthesis of untold numbers of organic compounds, both natural and unnatural, cannot be overstated. However, its impact on the field extends beyond the impressive applications in synthesis. The directed aldol reaction has served as a fertile proving ground for new concepts and new methods for stereocontrol and catalysis. This Minireview provides a case history of how the challenges of merging site selectivity, diastereoselectivity, enantioselectivity, and catalysis into a unified reaction manifold stimulated the development of Lewis base catalyzed aldol addition reactions. The evolution of this process is chronicled from the authors' laboratories as well as in those of Professor Teruaki Mukaiyama.

Highly diastereoselective Mannich-type reaction of titanium enolate derived from 2′-hydroxypropiophenone

Mannich-type addition of the titanium enolate derived from 2′-hydroxypropiophenone to N-tosylimines provided the corresponding β-aminoketones in good to excellent yields (60%–90%) and with >99 : <1 anti diastereoselectivity. A model for synthesis of anti β-aminoketone as a predominant isomer based on the titanium enolate has been developed. High anti selectivity is not independent of the electron-donating and electron-withdrawing groups on the phenyl ring of the N-tosylimines. Noteworthy is the observation that the influence of a second Lewis acid on the Mannich-type reaction based on the titanium enolate is opposite to that obtained from other titanium enolates reported. A reasonable mechanism has been proposed to explain the high anti diastereoselectivity and the effect of a second Lewis acid on yield.

Organocatalyzed enantioselective protonation of silyl enol ethers: scope, limitations, and application to the preparation of enantioenriched homoisoflavones

In the present work, enantioselective protonation of silyl enol ethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchona alkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved under mild and eco-friendly conditions. The synthetic utility of this organocatalytic protonation was demonstrated during the preparation of two homoisoflavones 4a and 4b, isolated from Chlorophytum Inornatum and Scilla Nervosa, which were obtained with 81% and 78% ee, respectively.

LiOAc-catalyzed chemoselective deprotection of aryl silyl ethers under mild conditions

An efficient and chemoselective deprotection protocol for aryl silyl ethers using LiOAc as a bifunctional Lewis acid-Lewis base catalyst was described. Acetates, epoxides, and aliphatic silyl ethers were preserved, whereas aryl TBS and TBDPS ethers can be differentiated.

An Easy Stereoselective Access to β,γ-Aziridino α-Amino Ester Derivatives via Mannich Reaction of Benzophenone Imines of Glycine Esters with N-Sulfonyl α-Chloroaldimines

Mannich-type addition of benzophenone imine glycinates across newly synthesized N-(p-toluenesulfonyl) alpha-chloroaldimines afforded gamma-chloro-alpha,beta-diamino ester derivatives with moderate diastereoselectivity as separable mixtures of anti and syn diastereomers. The gamma-chloro-alpha,beta-diamino esters were efficiently cyclized under basic conditions to the corresponding beta,gamma-aziridino alpha-amino ester derivatives, representing a new class of conformationally constrained heterocyclic alpha,beta-diamino acid derivatives. The relative configuration of the aziridines was determined via X-ray diffraction analysis. Mechanisms and intermediate transition states to explain the stereochemical outcome of the Mannich reaction with different substrates or under different conditions are proposed. The synthetic importance of the beta,gamma-aziridino alpha-amino ester derivatives is demonstrated by their conversion into the corresponding Boc-protected derivatives and ring opening reactions to alpha,beta-diamino esters and a gamma-amino alpha,beta-unsaturated amino ester.

Highly Diastereoselective Synthesis of β-Carboxy-γ-lactams and Their Ethyl Esters via Sc(OTf)3-Catalyzed Imino Mukaiyama-Aldol Type Reaction of 2,5-Bis(trimethylsilyloxy)furan with Imines

Functionalized gamma-lactams are found to be crucial intermediates in the synthesis of biologically important natural products. We herein described a highly diastereoselective synthesis of beta-carboxy-gamma-lactams and their ethyl ester derivatives, in high yields with high diastereomeric ratio, via the Mukaiyama-aldol type reaction of 2,5-bis(trimethysilyloxy)furan with imines, employing Sc(OTf)(3) as a catalyst.