Tunable Zinc-Mediated Reductive Cyclization of Diastereomeric 3-Nitro-4-phenacyl-2-(trihalomethyl)chromanes to Fused Pyrroline N-Oxides, Pyrrolines, and Pyrrolidines

Reductive cyclization of trans,trans- and trans,cis-isomers of the 2-CF3-substituted 3-nitro-4-phenacylchromanes with Zn-based reductive systems, depending on the conditions, affords 4-CF3-substituted 1,3a,4,9b-tetrahydrochromeno[3,4-b]pyrrole 3-oxides, 1,3a,4,9b-tetrahydrochromeno[3,4-b]pyrroles, or 1,2,3,3a,4,9b-hexahydrochromeno[3,4-b]pyrroles in good yields without changing the relative configuration of the pyran ring. A similar process involving the 2-CCl3-substituted 3-nitro-4-phenacylchromanes is accompanied by reductive dehalogenation to form the corresponding 4-dichloromethyl-substituted fused chromanes along with the 3-(2-hydroxyaryl)-2-(2,2-dichlorovinyl)-5-phenyl-2H-pyrroline 1-oxides as pyran ring opening products. The structure and relative configuration of the obtained products was reliably confirmed by X-ray diffraction analysis and 2D NMR spectroscopy.

Metal-mediated synthesis of pyrrolines

The five-membered, nitrogen-containing pyrroline ring is a privileged structure. This ring is present in many bioactive compounds from natural sources. Pyrrolines-the dihydro derivatives of pyrroles-have three structural isomer classes, depending on the location of the double bond: 1-pyrrolines (3,4-dihydro-2H-pyrroles), 2-pyrrolines (2,3-dihydro-1H-pyrroles) and 3-pyrrolines (2,5-dihydro-1H-pyrroles). This review aims to describe the latest advances for the synthesis of pyrrolines by transition metal-catalyzed cyclizations. Only reactions in which the pyrroline ring is formed by metal promotion are described. Transformations of the pyrroline ring in other heterocycles, and the structural manipulations of the pyrroline itself are not discussed. The review is organized into three parts, each covering the metal-mediated synthesis of the three pyrroline isomers. Each part is subdivided according to the metal involved, and concludes with a brief description of notable biological activities within the class.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

This review article provides a summary of the detrifluoroacetylativein situgeneration of fluorine-containing enolates and their related reactions.

Access to benzo-fused nine-membered heterocyclic alkenes with a trifluoromethyl carbinol moiety via a double decarboxylative formal ring-expansion process under palladium catalysis

Direct access to pharmaceutically attractive benzo-fused nine-membered heterocyclic alkenes 3 with a trifluoromethyl carbinol moiety was achieved via a palladium-catalyzed double-decarboxylative formal ring-expansion process from six-membered trifluoromethyl benzo[d][1,3]oxazinones 1 to nine-membered trifluoromethyl benzo[c][1,5]oxazonines 3 in the presence of vinylethylene carbonates 2. Generation of a Pd-π-allyl zwitterionic intermediate was proposed in the catalytic cycle. The trifluoromethyl group in the benzoxazinanones 1 plays an important role throughout the transformation. Diastereoselective chemical transformations of products 3 were also demonstrated.

Asymmetric [4+2] annulations to construct norcamphor scaffolds with 2-cyclopentenone via double amine–thiol catalysis

A double catalytic system combining chiral amine and 2-mercaptobenzoic acid is applied for α′,β-regioselective [4+2] annulations of 2-cyclopentenone with diverse activated alkenes.

Regioselective indole C2-alkylation using β-CF3-substituted enones under redox neutral Rh(iii) catalysis

Rhodium(iii) catalyzed C–H alkylation at the C2-position of indole with β-trifluoromethyl-α,β-unsaturated ketones with a broad range of substrates and excellent functional group compatibility is described.

Copper-Catalyzed Asymmetric Borylation: Construction of a Stereogenic Carbon Center Bearing Both CF3 and Organoboron Functional Groups

Copper-catalyzed borylation of β-trifluoromethyl-α,β-unsaturated ketones was efficiently achieved by means of bis(pinacolato)diboron (B₂pin₂), affording the enantioenriched products in good yields with high enantioselectivities. CuI and (R,S)-Josiphos consist of the most efficient catalyst system under mild conditions. In the absence of the chiral ligand, the reactions could be performed more efficiently to form β-ketone derivatives which were directly borylated and indirectly trifluoromethylated at the β-carbon atom of the α,β-unsaturated ketone substrates. The present protocol provides a promising method to access a stereogenic carbon center bearing both CF₃ and organoboron functional groups.

Asymmetric synthesis of CF3-containing tetrahydroquinoline via a thiourea-catalyzed cascade reaction

The first example of the asymmetric introduction of CF₃ into the 2-position of tetrahydroquinolines was described by using β-CF₃-nitroalkene as the building block.

Copper-catalysed enantioselective Michael addition of malonic esters to β-trifluoromethyl-α,β-unsaturated imines

A diastereo- and enantioselective Michael addition of methyl malonate to β-trifluoromethyl unsaturated imines is presented.

Diastereoselective synthesis of fluoroisosteric analogues of antiparasitic pyrrolobenzoxazine alkaloids from tryptophan by successive fluorination–cyclization and a Meisenheimer-type rearrangement

Fluoroisosteric analogues of an antiparasitic pyrrolobenzoxazine alkaloid CJ-12663 were designed and diastereoselectively synthesized.

Construction of Furan Derivatives with a Trifluoromethyl Stereogenic Center: Enantioselective Friedel-Crafts Alkylations via Formal Trienamine Catalysis

An asymmetric Friedel-Crafts alkylation reaction of 2-furfuryl ketones with β-trifluoromethyl enones has been developed via formal trienamine catalysis of a bifunctional primary amine-thiourea substance derived from L-tert-leucine, delivering the furan derivatives incorporating a stereogenic trifluoromethyl (CF₃) group in good to high yields with excellent enantioselectivity.

Cascade reaction for the construction of CF3 containing tetrasubstituted furan ring

Activated olefins are well known nucleophiles, but proton abstraction from the substituted α-methyl group in nitroolefin is rare.

Rhodium(iii)-catalyzed sp2 C–H bond addition to CF3-substituted unsaturated ketones

Rhodium(iii)-catalyzed conjugate addition of sp² C–H bonds to β-trifluoromethyl-α,β-unsaturated ketones was efficiently achieved.

Catalytic asymmetric conjugate addition of isocyanoacetate to (Z)-3-substituted-2-(4-pyridyl)-acrylonitrile, a reactive class of Michael acceptor

Un-substituted isocyanoacetate ethyl ester reacted with Michael acceptors 1a–m under the catalysis of Cinchona based quaternary ammonium salts providing imines 4a–m as a single diastereoisomer and in up to 94% ees.

Fluorine effects in organocatalysis - asymmetric Brønsted acid assisted Lewis base catalysis for the synthesis of trifluoromethylated heterocycles exploiting the negative hyperconjugation of the CF3-group

An efficient Brønsted acid assisted Lewis base catalysis protocol for the synthesis of enantiomerically pure trifluoromethylated dihydropyridazines starting from readily available hydrazones and α,β-unsaturated aldehydes has been developed. The reaction exhibits high tolerance towards many functional groups and is applicable to various aliphatic, aromatic and hetero-aromatic α,β-unsaturated aldehydes, and provides the products in good yields and with excellent enantioselectivities.

Catalytic asymmetric conjugate addition of terminal alkynes to β-trifluoromethyl α,β-enones

The first enantioselective conjugate alkynylation of β-trifluoromethyl α,β-enones using terminal alkynes and a taniaphos–Cu(i) complex as catalyst is described.