Catalytic Enantioselective Synthesis of Tetrahydrofurans: A Dynamic Kinetic Asymmetric [3 + 2] Cycloaddition of Racemic Cyclopropanes and Aldehydes

Dearomatization of electron poor six-membered N-heterocycles through [3 + 2] annulation with aminocyclopropanes

Dearomative [3 + 2] annulation of N-heterocycles with donor–acceptor aminocyclopropanes: fast access to indolizidine building blocks.

Many abundant and highly bioactive natural alkaloids contain an indolizidine skeleton. A simple, high yielding method to synthesize this scaffold from N-heterocycles was developed. A wide range of pyridines, quinolines and isoquinolines reacted with donor–acceptor (DA)-aminocyclopropanes via an ytterbium(iii) catalyzed [3 + 2] annulation reaction to give tetrahydroindolizine derivatives. The products were obtained with high diastereoselectivities (dr > 20 : 1) as anti-isomers. Additionally, the formed aminals could be easily converted into secondary and tertiary amines through iminium formation followed by reduction or nucleophile addition. This transformation constitutes the first example of dearomatization of electron-poor six-membered heterocycles via [3 + 2] annulation with DA cyclopropanes.

Catalytic Annulation of Diethyl Methylenecyclopropane-1,1-dicarboxylate with 1,1-Dicyanoalkenes

The catalytic annulation of methylenecyclopropane 1 with 1,1-dicyanoalkenes 2 using a Mg-Sn catalytic system was developed. Selective formation of cyclopentylidenemalonates 3 and spiro[2,3]hexane-1,1-dicarboxylates 4 was accomplished via the choice of a proper solvent and an effective catalytic system.

An enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones and 2-phthalimidoacrylates

A highly enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones to 2-phthalimidoacrylates has been developed using a bifunctional tertiary-amine thiourea catalyst.

Lewis acid catalyzed diastereoselective [3+4]-annulation of donor–acceptor cyclopropanes with anthranils: synthesis of tetrahydro-1-benzazepine derivatives

The [3+4]-annulation between donor–acceptor cyclopropanes and anthranils has been developed for the diastereoselective synthesis of tetrahydro-1-benzazepine derivatives.

Enantioselective magnesium-catalyzed transformations

This review updates the major progress in the field of enantioselective transformations promoted by chiral magnesium catalysts, covering the literature since 2007, illustrating the power of these green catalysts to promote many types of reactions.

Photochemical Stereocontrol Using Tandem Photoredox-Chiral Lewis Acid Catalysis

The physical, biological, and materials properties of organic compounds are determined by their three-dimensional molecular shape. The development of methods to dictate the stereochemistry of organic reactions has consequently emerged as one of the central themes of contemporary synthetic chemistry. Over the past several decades, chiral catalysts have been developed to control the enantioselectivity of almost every class of synthetically useful transformation. Photochemical reactions, however, are a conspicuous exception. Relatively few examples of highly enantioselective catalytic photoreactions have been reported to date, despite almost a century of research in this field. The development of robust strategies for photochemical enantiocontrol has thus proven to be a long-standing and surprisingly difficult challenge. For the past decade, our laboratory has been studying the application of transition metal photocatalysts to a variety of problems in synthetic organic chemistry. These efforts have recently culminated in the discovery of an effective system in which the activity of a visible light absorbing transition metal photoredox catalyst is combined with a second stereocontrolling chiral Lewis acid catalyst. This dual catalyst strategy has been applied to a diverse range of photochemical reactions; these have included highly enantioselective photocatalytic [2 + 2] cycloadditions, [3 + 2] cycloadditions, and radical conjugate addition reactions. This Account describes the development of the tandem Lewis acid photoredox catalysis strategy utilized in our laboratory. It provides an analysis of the factors that we believe to be particularly important to the success of this seemingly robust approach to photocatalytic stereocontrol. (1) The photocatalysts utilized in our systems are activated by wavelengths of visible light where the organic substrates are transparent, which minimizes the possibility of competitive racemic background photoreactions. (2) The high degree of tolerance that Ru(bpy)₃²⁺ and similar octahedral metal polypyridine complexes exhibit toward Lewis acids affords great flexibility in tuning the structure of the stereocontrolling chiral catalyst without perturbing the photoredox properties of the photocatalyst. (3) Synthetic chemists have amassed a substantial understanding of the features that are common in highly successful chiral Lewis acid catalyzed reactions, and these deep, well-validated insights are readily applied to the reactions of a variety of photogenerated intermediates. We hope that the recent success of this and similar dual catalytic systems will provide a useful foundation for the further development of powerful, stereocontrolled photochemical reactions.

Lewis Acid and (Hypo)iodite Relay Catalysis Allows a Strategy for the Synthesis of Polysubstituted Azetidines and Tetrahydroquinolines

A catalytic [3 + 1]-annulation reaction between cyclopropane 1,1-diester and aromatic amine is developed based on the relay catalysis strategy. Lewis acid-catalyzed nucleophilic ring opening of cyclopropane 1,1-diester with aromatic amine and (hypo)iodite-catalyzed C-N bond formation are combined successfully in one reaction. Using this reaction, biologically important azetidines and tetrahydroquinolines can be prepared directly.

Synergistic chiral iminium and palladium catalysis: Highly regio- and enantioselective [3 + 2] annulation reaction of 2-vinylcyclopropanes with enals

A cooperative catalytic strategy of chiral iminium catalysis by regioselective activation of the C=C bond in enals and a transition metal promoting to open the 2-vinylcyclopropanes for highly regio- and enantioselective [3 + 2] cycloaddition reaction of 2-vinylcyclopropanes with α,β-unsaturated aldehydes has been developed.

Asymmetric [3 + 2] cycloaddition of donor-acceptor aziridines with aldehydes via carbon-carbon bond cleavage

An enantioselective [3 + 2] annulation of donor-acceptor aziridines with aldehydes has been realized using a Nd(OTf)3/N,N'-dioxide/LiNTf2 catalyst system, providing various chiral cis-1,3-oxazolidines in moderate to good yields with high levels of stereocontrol. A relay catalytic process is proposed where LiNTf2 promotes the formation of azomethine ylide intermediates, and a chiral Nd(iii)-N,N'-dioxide complex accelerates the asymmetric cycloaddition.

Ag-catalyzed C-H/C-C bond functionalization

Silver, known and utilized since ancient times, is a coinage metal, which has been widely used for various organic transformations in the past few decades. Currently, the silver-catalyzed reaction is one of the frontier areas in organic chemistry, and the progress of research in this field is very rapid. Compared with other transition metals, silver has long been believed to have low catalytic efficiency, and most commonly, it is used as either a cocatalyst or a Lewis acid. Interestingly, the discovery of Ag-catalysis has been significantly improved in recent years. Especially, Ag(i) has been demonstrated as an important and versatile catalyst for a variety of organic transformations. However, so far, there has been no systematic review on Ag-catalyzed C-H/C-C bond functionalization. In this review, we will focus on the development of Ag-catalyzed C-H/C-C bond functionalization and the corresponding mechanism.

Enantioselective Photocatalytic [3 + 2] Cycloadditions of Aryl Cyclopropyl Ketones

Control of stereochemistry in photocycloaddition reactions remains a substantial challenge; almost all successful catalytic examples to date have involved [2 + 2] photocycloadditions of enones. We report a method for the asymmetric [3 + 2] photocycloaddition of aryl cyclopropyl ketones that enables the enantiocontrolled construction of densely substituted cyclopentane structures not synthetically accessible using other catalytic methods. These results show that the dual-catalyst strategy developed in our laboratory broadens synthetic chemists' access to classes of photochemical cycloadditions that have not previously been feasible in enantioselective form.

Synthesis of Chiral Tetrahydrofurans via Catalytic Asymmetric [3 + 2] Cycloaddition of Heterosubstituted Alkenes with Oxiranes

An efficient diastereo- and enantioselective [3 + 2] cycloaddition of heterosubstituted alkenes with oxiranes via selective C-C bond cleavage of epoxides has been developed. The reaction was catalyzed by a chiral N,N'-dioxide/Ni(II) catalyst, and a variety of chiral highly substituted tetrahydrofurans were obtained in up to 99% yield, 92/8 dr, and 99% ee.

Lewis acid catalyzed [3 + 2] annulation of ketenimines with donor–acceptor cyclopropanes: an approach to 2-alkylidenepyrrolidine derivatives

C,C,N-Trisubstituted ketenimines undergo [3 + 2] annulation reactions via its CN bond with donor–acceptor cyclopropanes triggered by Sc(OTf)₃ to yield a diversity of 2-alkylidene pyrrolidines.

Catalytic asymmetric [3 + 3] annulation of cyclopropanes with mercaptoacetaldehyde

A highly diastereo- and enantioselective [3 + 3] annulation of donor–acceptor cyclopropanes with mercaptoacetaldehyde has been developed.

One-Pot Catalytic Asymmetric Synthesis of Tetrahydrocarbazoles

A one-pot asymmetric synthesis of 1,2,3,4-tetrahydrocarbazoles has been developed via an enantioselective [3 + 3] annulation of 2-alkynylindoles and donor-acceptor cyclopropanes. In the presence of chiral Lewis acids as catalysts, a series of optically active tetrahydrocarbazoles were furnished in high yields (63-87%) with good to excellent levels of enantioselectivity (up to 94% ee).