Palladium-Catalyzed Asymmetric Formal [3+2] Cycloaddition of Vinyl Cyclopropanes and β,γ-Unsaturated α-Keto Esters: An Effective Route to Highly Functionalized Cyclopentanes

COAP-Pd Catalyzed Asymmetric Formal [3+2] Cycloaddition for Optically Active Multistereogenic Spiro Cyclopentane-Indandiones Bearing Cyclic N-Sulfonyl Ketimine Skeletons

We reported a chiral oxamide-phosphine ligand (COAP-Ph)-Pd-catalyzed asymmetric [3+2] cycloaddition reaction between vinyl cyclopropane compounds derived from 1,3-indanedione and 2-vinylcyclopropane-1,1-dicarboxylates with cyclic sulfonyl 1-azadienes. The corresponding reactions provided a series of enantiomerically active spiro cyclopentane-indandione and cyclopentane structures bearing three consecutive stereogenic centers in good yields with good diastereo- and enantioselectivity. The COAP-Pd complex serves not only to promote generation of chiral π-allyl-palladium intermediates and induce the asymmetry of the reaction, but also depress the background reaction.

Palladium-catalysed enantio- and regioselective (3 + 2) cycloaddition reactions of sulfamidate imine-derived 1-azadienes towards spirocyclic cyclopentanes

An enantio- and diastereoselective Pd-catalysed (3 + 2) cycloaddition of bis(trifluoroethyl) 2-vinyl-cyclopropane-1,1-dicarboxylate (VCP) with cyclic sulfamidate imine-derived 1-azadienes (SDAs) has been developed. These reactions provide highly functionalized spiroheterocycles having three contiguous stereocentres, including a tetrasubstituted carbon bearing an oxygen functionality. The two geminal trifluoroethyl ester moieties can be manipulated in a facially selective manner to afford more diversely decorated spirocycles with four contiguous stereocentres. In addition, diastereoselective reduction of the imine moiety can also afford a fourth stereocentre and exposes the important 1,2-amino alcohol functionality.

An endo-Directing-Group Strategy Unlocks Enantioselective (3+1+2) Carbonylative Cycloadditions of Aminocyclopropanes

An endo-directing group strategy enables enantioselective (3+1+2) cycloadditions that are triggered by carbonylative C-C bond activation of cyclopropanes. These processes are rare examples of cycloadditions where C-C bond oxidative addition is enantiodetermining, and the first where this is achieved within the context of a multicomponent (higher order) reaction design.

Enantioselective [3 + 2] Cycloaddition of Vinylcyclopropanes with Alkenyl N-Heteroarenes Enabled by Palladium Catalysis

The first catalytic enantioselective [3 + 2] cycloaddition reaction between vinylcyclopropanes and alkenyl N-heteroarenes in the presence of LiBr and a Pd(0)/SEGPHOS complex was developed. LiBr plays a key role in improving the reactivity of alkenyl N-heteroarenes as a mild Lewis acid.

Catalytic Asymmetric Synthesis of Chiral Thiohydantoins via Domino Cyclization Reaction of β,γ-Unsaturated α-Ketoester and N,N'-Dialkylthiourea

The first catalytic asymmetric route to synthesize chiral thiohydantoins containing a quaternary stereogenic center has been established utilizing a chiral phosphoric acid-catalyzed domino cyclization reaction of N,N'-dialkyl thioureas with β,γ-unsaturated...

Asymmetric Synthesis of 2,2-Difluorotetrahydrofurans through Palladium-Catalyzed Formal [3+2] Cycloaddition

The asymmetric synthesis of 2,2-difluorinated tetrahydrofurans was accomplished via enantioselective formal [3+2] cycloaddition catalyzed by palladium. The asymmetric reaction between gem-difluoroalkenes and racemic vinyl epoxides or vinylethylene carbonates resulted in the formation of enantioenriched 2,2-difluorotetrahydrofurans with an enantioselectivity up to 98 %. Notably, the reaction used the readily available (R)-BINAP as the ligand at a low loading and yielded a wide variety of difluorinated products in moderate to high yields. Both chiral diastereomers could be obtained in a single sequence.

Visible-Light-Induced Dearomatization of Indoles/Pyrroles with Vinylcyclopropanes: Expedient Synthesis of Structurally Diverse Polycyclic Indolines/Pyrrolines

Visible-light-induced cycloaddition reactions initiated via energy-transfer processes have recently evolved as powerful methods for the construction of strained cyclic molecules that are not easily accessed using known ground-state synthetic methods. Particularly, the reactions initiated by the excitation of aromatic rings provide an alternative solution to the direct transformations of aromatic feedstocks under the scheme of dearomatization. Vinylcyclopropanes (VCPs) are well-known reagents in radical clock experiments, working as a probe to detect transient radical intermediates. However, the synthetic applications in this regard still remain limited due to uncontrollable selectivities. Herein, we report visible-light-induced dearomatization of indole- or pyrrole-tethered VCPs, in which several competitive reaction pathways, including [5 + 2], [2 + 2], interrupted [5 + 2], and [5 + 4] cycloadditions, can be well regulated by engineering substrate structures and tuning reaction conditions. The reaction mechanism has been explored by combined experimental and computational investigations. These reactions provide a convenient method to synthesize structurally diverse polycyclic molecules with high efficiency and good selectivity.

Palladium-Catalyzed Cascade to Benzoxepins by Using Vinyl-Substituted Donor-Acceptor Cyclopropanes

A palladium-catalyzed intermolecular cascade (4+3) cyclocondensation of salicylaldehydes and vinylcyclopropanes is reported. A key feature of the reaction is the use of a phosphonate group as an acceptor moiety on the cyclopropane, exploiting its propensity to undergo olefination with aldehydes. Subsequent O-allylation enabled the formation of a range of substituted benzoxepinsWith a novel chiral ligand, the products were obtained in generally good yield and with reasonable enantioselectivity.

Enantioselective formal [3+2]-cycloadditions to access spirooxindoles bearing four contiguous stereocenters through synergistic catalysis

An enantioselective ring-opening formal [3+2]-cycloaddition of spirovinylcyclopropyl oxindoles with enals via synergistic catalysis of palladium(0) and a chiral organocatalyst has been developed, affording spirooxindoles bearing four contiguous stereocenters in good yields with excellent enantioselectivities. The generality and utility of the protocol were also demonstrated through scale-up experiments and synthetic transformation of the resulting cycloadduct.

Vinylcyclopropanes as All-Carbon 1,5-Dipoles: A Reactivity Switch for Palladium-Catalyzed (5 + 4) Cycloadditions

Azonanes were prepared by a palladium-catalyzed (5 + 4) cycloaddition between activated vinylcyclopropanes and 1-azadienes. During this process, the vinylcyclopropane partner displayed an unusual reactivity and behaved as an all-carbon 1,5-dipole. A N,N-bidentate ligand was required to inhibit the formation of thermodynamic (3 + 2) cycloadducts.

Construction of Chiral Isotetronic Acid-Fused Thiochromane via Doubly Annulative Strategy

A sulfa-Michael/aldol/lactonization cascade reaction has been established to construct isotetronic acid-fused thiochromanes in a highly stereoselective fashion (≥11:1 dr, 35-98% ee). The tricyclic products were obtained in 35-99% isolated yields in the presence of a bifunctional squaramide. Three reactive sites of β,γ-unsaturated α-ketoester, including the less-explored ester carbonyl group, were sequentially utilized to construct two fused heterocycles in a one-pot operation.

Development of Dipolarophiles for Catalytic Asymmetric Cycloadditions through Pd-π-Allyl Zwitterions

The development of new and efficient methodology for the construction of optically active molecules is of great interest in both synthetic organic and medicinal chemistry fields. To this end, the personal account summarizes our studies on the development of electron-deficient alkenes, allenes, and alkynes containing single activator as new dipolarophiles for Pd-catalyzed asymmetric cycloaddition reactions. These new dipolarophiles can participate in Pd-catalyzed asymmetric [3+2] and [4+2] cycloadditions through Pd-π-allyl 1,3- and 1,4-zwitterions in-situ generated by the reaction of Pd(0) catalyst with vinyl aziridines, vinyl epoxides, vinyl cyclopropanes, 4-vinyl-1,3-dioxan-2-ones, and vinyl benzoxazinanones. These [3+2] and [4+2] cycloadditions provide efficient approaches to a wide range of enantiomerically enriched five- and six-membered ring compounds containing contiguous chiral centers with high to excellent chemo-, diastereo-, and enantioselectivities. The utilities of these protocols are demonstrated by transformation of the cycloadducts into other useful chiral building blocks. DFT calculations reveal the dissimilar reactivity of different electron deficient alkenes and rationalize the mechanism and stereo-control of the reaction. A Pd-catalyzed inverse [3+2] cycloaddition is disclosed.

Regio- and enantioselective ring-opening reaction of vinylcyclopropanes with indoles under cooperative catalysis

The title reaction has been established under the cooperative bimetallic catalysis of iridium and copper catalysts, which afforded indole C3-allylation products with branched selectivity in moderate yields and good enantioselectivities.

Visible-light-induced, catalyst and additive-free cycloaddition of vinylcyclopropanes: access to sulfur-containing seven-membered heterocycles

The first visible-light-induced, catalyst and additive-free protocol for [5 + 2] cycloadditions of vinylcyclopropanes (VCPs) has been achieved.

Construction of cyclopenta[b]pyran-2-ones via chemoselective (3 + 2) cycloaddition between 2-pyrones and vinyl cyclopropanes

A chemoselective (3 + 2) cycloaddition of 2-pyrones and vinyl cyclopropanes for efficient and diastereoselective synthesis of cyclopenta[b]pyran-2-ones.

Palladium-catalysed ring-opening [3 + 2]-annulation of spirovinylcyclopropyl oxindole to diastereoselectively access spirooxindoles

A novel palladium-catalysed ring-opening [3 + 2]-annulation of spirovinylcyclopropyl oxindole with α,β-unsaturated nitroalkenes is reported. A series of spirooxindole derivatives were synthesized in high yields and good to excellent diastereoselectivities. This developed protocol offers a new and efficient pathway for the assembly of spirooxindoles.

Palladium-catalyzed asymmetric formal [3+2] cycloaddition of α-N-heterocyclic acrylates with vinyl epoxides for construction of isonucleoside analogs

A highly efficient Pd-catalyzed asymmetric formal [3+2] cycloaddition of α-N-heterocyclic acrylates with vinyl epoxides has been developed for the first time.

Palladium-catalyzed diastereo- and enantioselective formal [3 + 2] cycloaddition of vinyl cyclopropanes with cyclic 1-azadienes

We have developed highly efficient and stereoselective Pd-catalyzed formal [3 + 2] cycloadditions of vinyl cyclopropanes with cyclic 1-azadienes.

Synthetic applications of vinyl cyclopropane opening

Vinyl cyclopropanes are amongst the most useful building blocks in organic synthesis. Their easy opening and capacity to generate dipoles have been exploited for the synthesis of cyclopentanes with good yields and sometimes excellent stereoselectivities. In this review we give an overview of their applications, focusing on the present century.

Pd-catalyzed [3 + 2] cycloaddition of vinylcyclopropanes with 1-azadienes: synthesis of 4-cyclopentylbenzo[e][1,2,3]oxathiazine 2,2-dioxides

The palladium-catalyzed [3 + 2] cycloaddition of vinylcyclopropanes and 1-azadienes has been developed under mild reaction conditions, giving the multisubstituted cyclopentane derivatives in good to excellent yields with moderate to good diastereoselectivities. The relative configuration of both diastereomers of the products have been determined through X-ray crystallographic diffraction.

Pd-catalyzed [3 + 2] cycloaddition of vinylcyclopropanes with 1-azadienes gave highly functionalized cyclopentane derivatives in high yields.

Asymmetric ring-opening of cyclopropyl ketones with β-naphthols catalyzed by a chiral N,N′-dioxide–scandium(iii) complex

An efficient asymmetric ring-opening reaction of cyclopropyl ketones with 2-naphthols has been realized using a chiral N,N′-dioxide–Sc^III complex catalyst. A variety of chiral β-naphthol derivatives were obtained in excellent outcomes (up to 99% yield, 97% ee).

Pd-Catalyzed diastereoselective [3 + 2] cycloaddition of vinylcyclopropanes with sulfamate-derived cyclic imines

The palladium-catalyzed diastereoselective [3 + 2] cycloaddition reaction of vinylcyclopropanes with sulfamate-derived cyclic imines worked efficiently under mild conditions, providing sulfamate-fused pyrrolidines in good to excellent yields.

Lewis acid-catalyzed enantiospecific [3 + 2] annulations of γ-butyrolactone fused cyclopropanes with aromatic aldehydes: synthesis of chiral furanolignans

An enantiospecific [3 + 2] annulation of γ-butyrolactone fused cyclopropanes with aromatic aldehydes was realized to construct chiral furanolignans.

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

Stereoconvergent catalysis is an important subset of asymmetric synthesis that encompasses stereoablative transformations, dynamic kinetic resolutions, and dynamic kinetic asymmetric transformations. Initially, only enzymes were known to catalyze dynamic kinetic processes, but recently various synthetic catalysts have been developed. This Review summarizes major advances in nonenzymatic, transition-metal-promoted dynamic asymmetric transformations reported between 2005 and 2015.

"Cut and Sew" Transformations via Transition-Metal-Catalyzed Carbon-Carbon Bond Activation

The transition metal-catalyzed "cut and sew" transformation has recently emerged as a useful strategy for preparing complex molecular structures. After oxidative addition of a transition metal into a carbon-carbon bond, the resulting two carbon termini can be both functionalized in one step via the following migratory insertion and reductive elimination with unsaturated units, such as alkenes, alkynes, allenes, CO and polar multiple bonds. Three- or four-membered rings are often employed as reaction partners due to their high ring strains. The participation of non-strained structures generally relies on cleavage of a polar carbon-CN bond or assistance of a directing group.