Multicomponent reactions of phosphines, enynedioates and cinnamaldimines generated 3‐phosphorus ylide γ‐lactams having a 1,3,5‐hexatriene moiety with low activation energy barrier for 6π electrocyclization, through initial formation of 1,3‐dipoles from the α(δ′)‐Michael addition of phosphines to enynedioates. The reactive 1,3‐dipoles underwent addition to cinnamaldimines, lactamization, 6π electrocyclization and oxidation to give 3‐phosphorus ylide oxindoles as platform molecules toward isatins and isoxazolinones. The key step, 6π electrocyclization, was further examined by a kinetic and a computational study.
In the presence of sodium carbonate, the [4+3] cycloadditions of α‐halogeno hydrazones with nitrones were performed efficiently, and affording 2,3,4,7‐tetrahydro‐1,2,4,5‐oxatriazepines in moderate to high yields.
Multifunctional 3‐amino‐4‐dialkylphosphono‐2‐quinolinones have been prepared by “one‐pot” nucleophilic addition and regioselective ring enlargement of imino isatins. The addition reaction between imino isatins and dialkyl (diazomethyl)phosphonate proceeds smoothly using potassium carbonate as a catalyst, and a subsequent regioselective ring expansion promotes by salicylic acid to afford the desired products in high yields.
A metal‐free vinylic carbon‐hydrogen bond thiolation has been developed. Under the catalysis of iodine (10 mol%), the cyclization of α‐alkenoyl ketene dithioacetals afforded a broad range of polyfunctionalized 2‐methylene‐3‐thiophenones in good selectivity with moderate to excellent yields via tandem iodocyclization and dehydroiodination. The synthetic strategy can also be extended to the cyclization of ortho‐methylthiophenyl vinyl ketones leading to 2‐methylene‐3‐benzothiophenones.
A one‐pot transformation of aldehydes into α,β‐unsaturated aldehydes was developed using both N‐benzyl‐N‐methylamine and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) as catalysts and MnO2 as a terminal oxidant. An oxidative and enantioselective reaction of aldehydes and nitromethane was established using both diphenylprolinol silyl ether and DDQ as a catalyst with MnO2 as a terminal oxidant, in which synthetically important β‐substituted γ‐nitro aldehydes were obtained with excellent enantioselectivity.
An efficient and practical decarboxylative double benzylation method for various 2‐picolinic acids has been established by using a bimetallic catalytic system of palladium(II) chloride (PdCl2) and silver(I) oxide (Ag2O), which offered a variety of diarylmethane derivatives with moderate to good yields.
A practical and novel process for the decarboxylative fluorination of β‐ketoacids in water in the presence of phase transfer catalyst has been developed, affording a series of α‐fluoroketones in good to excellent yields. Furthermore, a preliminary investigation for the catalytic asymmetric transformation was performed and a proposed mechanistic pathway for this catalytic process was proposed.
The dynamic kinetic resolution of α‐substituted racemic β‐lactams by alcoholytic ring‐opening, catalyzed by immobilized lipase B from Candida antarctica is described. With this process, a variety of racemic α‐substituted N‐Cbz‐azetidinones (Cbz=benzyloxycarbonyl) was transformed to the corresponding N‐Cbz‐protected β2‐amino acid allyl esters with high enantioselectivity (up to 99%) and high yields (up to quantitative) at room temperature.
A simple and efficient ligand‐free nickel‐based catalytic system has been developed for the 1,4‐addition of arylboronic acids to α,β‐unsaturated carbonyl compounds. With catalyst loadings of 1–2 mol%, a series of 1,4‐adducts from chalcones and cinnamates was obtained in moderate to excellent yields within 5–30 min under a nitrogen atmosphere and microwave irradiation. The 1,4‐addition of arylboronic acids to acrylates is less efficient.
An unprecedented organocatalytic enantioselective cascade Michael/hemiketalization/retro‐aldol reaction of 2‐[(E)‐2‐nitrovinyl]phenols and 2,4‐dioxo‐4‐arylbutanoates is described. With a bifunctional squaramide catalyst incorporating (1R,2R)‐1,2‐diphenylethane‐1,2‐diamine, the reactions afford products in 75–99% yields with 80–98% ee. This process provides an enantioselective pathway for the synthesis of chiral α‐keto esters, precursors of 3‐arylproline derivatives, δ‐amino α‐keto acids or cyclic α‐keto lactams.
α‐Substituted β‐acetyl amides could undergo C C bond cleavage to form α‐keto amides when treated with copper(II) chloride (CuCl2) and boron trifluoride diethyl etherate (BF3⋅OEt2) under an oxygen atmosphere. The yield can be increased by the addition of tert‐butyl hydroperoxide which alone can also effect the reaction. The reaction provides a new protocol for the synthesis of α‐keto amides.
A direct enantioselective reaction of cyclopent‐2‐enone‐derived Morita–Baylis–Hillman alcohols with 4‐hydroxycoumarins has been developed under the catalysis of a chiral primary amine derived from cinchonine in combination with a Brønsted acid. The reaction provides pyranocoumarin products with three vicinal chiral carbon centers in highly regio‐, diastereo‐ and enantioselectivities through a tandem allylic alkylation/intramolecular oxa‐Michael addition.
A simple N‐heterocyclic carbene (NHC) derived from 1‐methyl‐3‐ethylimidazolium tetrafluoroborate was found to be an efficient ligand for a range of copper‐catalyzed cross‐coupling reactions, leading to the formation of aromatic ethers and thioethers.
The catalytic asymmetric [4+2] annulations of isatins with but‐3‐yn‐2‐one catalyzed by the Cinchona alkaloids‐derived oragnocatalyst (DHQD)2PHAL have been developed in the presence of 3.0 equivalents of D ‐diethyl tartrate in the mixed solvent (diphenyl ether/diethyl ether=1/1) or a slightly modified one, affording the corresponding substituted spiro[indoline‐3,2′‐pyran]‐2,4′(3′H)‐diones in good to excellent yields with high enantioselectivities under mild conditions.
A copper‐mediated, chelation‐assisted ortho C H bond nitration of benzoic acid derivatives using sodium nitrite as the source of the nitro group has been achieved with the aid of an 8‐aminoquinoline directing group. Selective mono‐ or dinitration can be achieved by simply changing the reaction conditions. The method shows excellent functional group tolerance and provides a novel and straightforward route for the preparation of ortho‐nitrated benzoic acids.
The first successful gold(I)‐catalyzed reaction of aryl aldehydes with trimethyl(arylethynyl)silanes to furnish bis‐alkynylated derivatives is reported. Key C C bond‐forming events involved in the catalytic cycle are analyzed.
