One-Pot Allylation-Intramolecular Vinylogous Michael Addition-Isomerization Cascade of o-Hydroxycinnamates and Congeners: Synthesis of Substituted Benzofuran Derivatives

A unique intramolecular vinylogous Michael addition leading to the synthesis of heterocycles has been disclosed. Base-promoted one-pot sequential O-allylation of o-hydroxy-cinnamates or -cinnamonitrile or -chalcones with γ-bromocrotonates followed by an intramolecular conjugate addition of vinylogous Michael donors resulted in the formation of highly substituted benzofuran derivatives in good to excellent yields. The intramolecular event followed by two [1,3]-H shifts leading to aromatization appears to be the key to the success of this unprecedented transformation.

Site-Selective and Enantioselective α,β,γ-Functionalization of 5-Alkylidenefuran-2(5 H)-ones: A Route to Polycyclic γ-Lactones

A new strategy for a direct α,β,γ-functionalization of the γ-lactone framework in the corresponding 5-alkylidenefuran-2(5 H)-ones is reported. The developed approach is based on a stereocontrolled cascade reaction with 2-mercaptocarbonyl compounds proceeding in a sequence of thia-Michael/aldol/oxa-Michael reactions. Such a synthetic strategy allows for a construction of a unique polycyclic architecture containing γ-lactone, tetrahydrofuran, and tetrahydrothiophene ring systems. Excellent enantioselectivities and diastereoselectivities have been obtained in the presence of bifunctional catalyst derived from cinchona alkaloids.

Effects of solvents on the DACBO-catalyzed vinylogous Henry reaction of isatin with 3,5-dimethyl-4-nitroisoxazole "on-water" and in solution from QM/MM MC simulations

The mechanism of the DABCO-catalyzed vinylogous Henry reaction of isatin with 3,5-dimethyl-4-nitroisoxazole and solvent effects on it have been investigated using density functional theory (DFT) methods and QM/MM Monte Carlo (MC) simulation under “on-water” conditions as well as in methanol and THF solutions. The DFT calculations concluded that Path A, in which DABCO directly catalyzes the reaction of isatin 1a with 3,5-dimethyl-4-nitroisoxazole 2 in water, is the most favorable and the first step, the proton transfer process, is the rate-determining step for the reaction. For the roles of solvents in the reaction, QM/MM MC simulations using free energy perturbation theory and PDDG/PM3 as the QM method have been utilized to predict the free energy profiles. The results indicated that the QM/MM method reproduced well the large rate increases on-water. Solute–solvent energy pair distribution and radial distribution functions were also analyzed and illustrated that hydrogen bonding plays a significant role in stabilizing the transition structures. This work reveals the feasible reaction mechanisms and provides new insight into solvent effects for the DACBO-catalyzed vinylogous Henry reaction.

QM/MM MC simulations indicate that the special hydrogen bonding effects are the main source of the rate enhancement of the title reaction on water.

A chiral-at-metal asymmetric catalyzed vinylogous Michael addition of ortho-methyl aromatic nitro compounds for isoxazole derivative synthesis

A chiral-at-metal rhodium(iii) complex catalyzed asymmetric vinylogous Michael addition of 5-methyl 4-nitroisoxazoles with α,β-unsaturated 2-acyl imidazoles has been developed, delivering the corresponding adducts with up to 96% yield and 97% ee.

A vinylogous Michael addition-triggered quadruple cascade reaction for the enantioselective generation of multiple quaternary stereocenters

An efficient organocatalytic vinylogous Michael addition-triggered quadruple cascade reaction resulting in fused spiroxindoles bearing multiple quaternary stereocenters is demonstrated from β-trifluoroacetylarylidene indanediones and 3-alkylideneoxindoles.

Highly enantioselective sequential vinylogous aldol reaction/transesterification of methyl-substituted olefinic butyrolactones with isatins for the construction of chiral spirocyclic oxindole-dihydropyranones

A highly stereoselective sequential vinylogous aldol reaction/transesterification of methyl-substituted olefinic butyrolactones and isatins was developed with 10 mol% Takemoto's amine–thiourea catalyst.

Enantioselective Functionalization of Enamides at the β-Carbon Center with Indoles

We report an enantioconvergent approach for the functionalization of enamides at the β-carbon atom, which involves a chiral Brønsted acid induced tautomerization of 2-amidoallyl into 1-amidoallyl cations. These putative reactive intermediates were produced by ionization of racemic α-hydroxy enamides with a chiral Brønsted acid and captured with substituted indoles in a highly regio- and enantioselective manner.

Enantioselective Mukaiyama-Michael Reaction Catalyzed by a Chiral Rhodium Complex Based on Pinene-Modified Pyridine Ligands

The rhodium complex Λ-Rh1 containing chiral pinene-modified pyridine ligands is prepared through a two-step synthetic procedure; it exhibits excellent reactivity and enantiocontrol towards the enantioselective Mukaiyama-Michael reaction of α,β-unsaturated 2-acyl imidazoles with silyl enol ethers, affording enantioenriched 1,5-dicarbonyl compounds in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee).

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Asymmetric and Site-Selective [3 + 2]-Annulations for the Synthesis of High-Value Bicyclic Lactams

Asymmetric and site-selective formal [3 + 2]-annulations of γ-alkyl-β,γ-unsaturated γ-lactams with α,β-unsaturated aldehydes have been developed. These organocatalysed transformations yield high value enantioenriched bicyclic γ-lactams with up to four new stereocenters (sometimes including a quarternary carbon). The overall transformation starts from simple and readily accessible furans and oversees a rapid, controlled, and dramatic enhancement in 3D complexity.

Brønsted base-catalyzed annulation of allyl ketones and alkynyl 1,2-diketones

The Cs₂CO₃-catalyzed reaction of allyl ketones and alkynyl 1,2-diketones affords a series of 2-acyloxycyclopent-3-enones under mild conditions. A unique α-selective addition/aldol reaction/C–C bond cleavage mechanism was proposed and supported by DFT calculations.

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

γ-Butenolides, γ-butyrolactones, and derivatives, especially in enantiomerically pure form, constitute the structural core of numerous natural products which display an impressive range of biological activities which are important for the development of novel physiological and therapeutic agents. Furthermore, optically active γ-butenolides and γ-butyrolactones serve also as a prominent class of chiral building blocks for the synthesis of diverse biological active compounds and complex molecules. Taking into account the varying biological activity profiles and wide-ranging structural diversity of the optically active γ-butenolide or γ-butyrolactone structure, the development of asymmetric synthetic strategies for assembling such challenging scaffolds has attracted major attention from synthetic chemists in the past decade. This review offers an overview of the different enantioselective synthesis of γ-butenolides and γ-butyrolactones which employ catalytic amounts of metal complexes or organocatalysts, with emphasis focused on the mechanistic issues that account for the observed stereocontrol of the representative reactions, as well as practical applications and synthetic potentials.

An asymmetric vinylogous Mukaiyama–Michael reaction of α,β-unsaturated 2-acyl imidazoles catalyzed by chiral Sc(iii)– or Er(iii)–pybox complexes

A highly diastereo- and enantioselective vinylogous Mukaiyama–Michael reaction of silyloxyfurans with α,β-unsaturated 2-acyl imidazoles catalyzed by either chiral Sc(iii) or Er(iii) complexes of a pybox ligand has been reported.

Phase-transfer catalyzed asymmetric synthesis of α,β-unsaturated γ,γ-disubstituted γ-lactams

The direct, γ-selective vinylogous Michael addition of unsaturated γ-monosubstituted γ-lactams was realized by using chiral phase-transfer catalysis.

Direct vinylogous oxidative cross-dehydrogenative coupling of 4-nitroisoxazoles with N-aryl tetrahydroisoquinolines in water under air conditions

Using water as the solvent and air as the oxidant, a direct catalytic vinylogous cross-dehydrogenative coupling reaction was developed.

Asymmetric synthesis of new γ-butenolides via organocatalyzed epoxidation of chalcones

A greener three-step sequence, with only one single chromatographic purification, afforded γ-butenolides in moderate overall yield and high enantiomeric excess.

Unique site-selectivity control in asymmetric Michael addition of azlactone to alkenyl dienyl ketones enabled by P-spiro chiral iminophosphorane catalysis

Simultaneous recognition of distance and direction of conjugation from carbonyl in alkenyl dienyl ketones enables a highly site-selective asymmetric 1,6-addition.

Direct Diastereo- and Enantioselective Vinylogous Michael Additions of Linear Enones

A direct vinylogous Michael addition using linear vinylogous Michael donors has been developed. Notably, even γ-substituted Michael donors cleanly afforded γ-alkylated products in high yield and ee by this method. Moreover, control experiments revealed that, for these and related linear vinylogous Michael donors, the size of the Michael acceptor strongly influences whether α- or γ-alkylation occurs, not simply blocking effects of cocatalysts as suggested previously.