Catalytic asymmetric conjugate addition of coumarins to unsaturated ketones catalyzed by a chiral-at-metal Rh(III) complex

The first catalytic asymmetric vinylogous Michael addition of coumarins to unsaturated ketones catalyzed by chiral rhodium catalysts has been established. This strategy allowed the synthesis of a variety of highly enantioenriched compounds containing coumarin skeletons in 41-99% yields and 84-99% ee. The developed reaction enriches the chemistry of catalytic asymmetric vinylogous Michael additions of 3-cyano-4-methylcoumarins. Furthermore, the protocol showed obvious advantages in reaction enantioselectivity. When the chiral rhodium catalyst was reduced to 0.06 mol%, a Gram-level reaction was still achieved to provide the desired products with 99% ee.

Catalytic Asymmetric Conjugate Addition of 2-Methyl-3,5-dinitrobenzoates to Unsaturated Ketones

Asymmetric catalytic vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates to unsaturated ketones catalyzed by chiral rhodium catalysts has been established. This strategy allowed the synthesis of a variety of optically pure compounds containing imidazole and 3,5-dinitrobenzene skeletons in 64-98% yields with 88-98% ee. The developed reaction not only represents highly asymmetric catalytic enantioselective vinylogous Michael addition employing 2-methyl-3,5-dinitrobenzoates as a building block but also enriches the chemistry of catalytic asymmetric vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates. Furthermore, the protocol showed obvious advantages in reaction activity and enantioselectivity. When the chiral rhodium catalyst was reduced to 0.06 mol %, the gram-level reaction was still achieved to provide the desired product with 95% ee.

Catalytic Diastereo- and Enantioselective Synthesis of Tertiary Trifluoromethyl Carbinols through a Vinylogous Aldol Reaction of Alkylidenepyrazolones with Trifluoromethyl Ketones

A diastereo- and enantioselective organocatalytic aldol reaction between alkylidenepyrazolones and trifluoromethyl ketones leading to chiral tertiary alcohols bearing a trifluoromethyl group is presented. The methodology is based on the use of a bifunctional organocatalyst in order to activate the γ-hydrogen atoms of the alkylidenepyrazolone nucleophile and the carbonyl group of the trifluoromethylarylketone providing highly functionalized trifluoromethyl alcohols with moderate yields, excellent diastereoselectivity, and moderate to good enantioselectivity. Experiments monitoring the conversion by ¹H NMR and the enantiomeric excess by HPLC with the reaction time showed that full conversion of the starting materials is not achieved and that the enantiomeric excess decreases upon extended times, probably due to the reversibility of the reaction.

An Electrochemical Way to Generate Amphiphiles from Hydrazones for the Synthesis of 1,2,4-Triazole Scaffold Cyclic Compounds

An electro-oxidative cyclization pathway in which hydrazones are selected as starting materials to generate amphiphiles by reacting with benzylamines and benzamides was reported. This strategy successfully prepared a series of 1,2,4-triazoles in satisfactory yields. Moreover, the use of cheap stainless steel as the anode, the feasibility to conduct the transformation as a one-pot reaction and the proof that scaling-up these reactions is possible make this transformation attractive for potential application in industry.

Regioselective α-addition of vinylogous α-ketoester enolate in organocatalytic asymmetric Michael reactions: enantioselective synthesis of Rauhut–Currier type products

Catalytic asymmetric α-regioselective Michael additions of vinylogous α-ketoester enolate are described herein.

Catalytic Diastereo- and Enantioselective Vinylogous Mannich Reaction of Alkylidenepyrazolones to Isatin-Derived Ketimines

A valuable organocatalytic vinylogous Mannich reaction between alkylidenepyrazolones and isatin-derived ketimines has been successfully established. Squaramide organocatalyst, prepared from quinine, catalyzed the diastereo- and enantioselective vinylogous Mannich addition, affording a range of aminooxindole-pyrazolone adducts (24 examples) with excellent outcomes: up to 98% yield with complete diastereoselectivity and excellent enantioselectivity (up to 99% ee). Additionally, different synthetic transformations were performed with the chiral pyrazolone-oxindole adducts.

Rubazonic Acids and Their Synthesis

Rubazonic acids are a class of dyes that are long-known, but studies on their syntheses and uses are rare. We now describe an experimentally simple and highly practical one-pot procedure for their synthesis starting from easily accessible 1H-pyrazol-5(4H)-ones. This protocol provides direct access to a broad range of the desired rubazonic acid derivatives through oxidative diazidation combined with a reductive work-up, without the need to isolate the potentially hazardous diazido compounds generated en route the target compounds. We also show how more challenging variants of rubazonic acid are efficiently prepared using an alternative two-step procedure and controlled hydrogenation conditions.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Stereoselective synthesis of spirocyclohexadiene-pyrazolones via organic base and/or hydrogen bonding assisted [3 + 3] annulation reactions

A DABCO and a chiral hydrogen bonding-assisted catalyzed [3 + 3] cycloaddition of α-arylidene pyrazolinones and 2-benzylidenemalononitriles provided spirocyclohexadiene-pyrazolones with all-carbon quaternary centers in good yields with excellent ees and moderate to high drs.

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.

Combined inorganic base promoted N-addition/[2,3]-sigmatropic rearrangement to construct homoallyl sulfur-containing pyrazolones

The first sequentially combined inorganic base promoted N-addition/[2,3]-sigmatropic rearrangement reaction of α-alkylidene pyrazolinones and propargyl sulfonium salts has been reported to construct homoallyl sulfur-containing pyrazolones with moderate to excellent yields. α-Alkylidene pyrazolinones function as N-nucleophilic agents distinguished from the reported C-addition reactions. Propargyl sulfonium salts were first involved in the [2,3]-sigmatropic rearrangement protocol differentiated from the well-established annulation reactions. The excellent regioselectivity, the broad scope of substrates, gram-scale synthesis and convenient transformation embody the synthetic superiority of this cascade process.

The combined inorganic base promoted N-addition/[2,3]-sigmatropic rearrangement of α-alkylidene pyrazolinones and propargyl sulfonium salts has been reported to construct homoallyl sulfur-containing pyrazolones with moderate to excellent yields.

Bismuth(III)-Promoted Trifluoromethylthiolation of Pyrazolin-5-ones with Trifluoromethanesulfenamide

An efficient and facile method for the synthesis of trifluoromethylthiolated 5-hydroxy-1H-pyrazole derivatives by reaction of pyrazolin-5-ones with trifluoromethanesulfenamide (PhNHSCF₃) in the presence of BiCl₃ was developed.

Recent Advances in Asymmetric Organocatalyzed Conjugate Additions to Nitroalkenes

The asymmetric conjugate addition of carbon and heteroatom nucleophiles to nitroalkenes is a very interesting tool for the construction of highly functionalized synthetic building blocks. Thanks to the rapid development of asymmetric organocatalysis, significant progress has been made during the last years in achieving efficiently this process, concerning chiral organocatalysts, substrates and reaction conditions. This review surveys the advances in asymmetric organocatalytic conjugate addition reactions to α,β-unsaturated nitroalkenes developed between 2013 and early 2017.

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.

An asymmetric assembly of spirooxindole dihydropyranones through a direct enantioselective organocatalytic vinylogous aldol-cyclization cascade reaction of 3-alkylidene oxindoles with isatins

An unexpected enantioselective organocatalytic vinylogous aldol-cyclization cascade reaction generating dihydropyranones in good to excellent yields with high enantioselectivities.

Direct asymmetric vinylogous Michael addition of 3-alkylidene oxindoles to chalcones catalyzed by a chiral N,N′-dioxide ytterbium(iii) complex

A chiral ytterbium(iii)–N,N′-dioxide complex was applied in the catalytic direct asymmetric vinylogous Michael addition of 3-alkylidene oxindoles to chalcones, giving the corresponding γ-addition products with high yields, enantioselectivities andZ/Eselectivities.

An asymmetric allylic alkylation reaction of 3-alkylidene oxindoles

An efficient asymmetric allylic alkylation reaction with respect to 3-alkylidene oxindoles and racemic MBH carbonate has been achieved.

Asymmetric synthesis of pyrazoles and pyrazolones employing the reactivity of pyrazolin-5-one derivatives

The various catalytic asymmetric strategies employing organo- and metal-catalysts utilized pyrazolin-5-one derivatives for the synthesis of potentially bioactive enantiopure pyrazoles and pyrazolones are presented.