A radical combination: An intermolecular cascade reaction involving alkyl halides, CO, electron-deficient alkenes, and stannyl enolates proceeds smoothly by a radical chain pathway to give four-component coupling products in good to high yields (see scheme). A series of 1,5-diketones with a substituent at the 3-position was prepared by this method.
Free-radical carbonylation of ω-alkynylamines with tributyltin hydride gives a mixture of α-methylene lactams and α-stannylmethylene lactams. Nucleophilic addition of an internal amino group to the carbonyl group of α-ketenyl radicals is proposed as the cyclization step. The subsequent unusual 1,4-H shift from the resulting 1-hydroxyallyl radical, followed by elimination of the β-tributyltin radical leads to the formation of α-methylene lactams.
The Mizoroki−Heck reaction was carried out using a fluorous ether F-626 as the solvent and a fluorous Pd carbene complex as the catalyst. When carboxylic acids are the products, separation of both the F-626 and the Pd catalyst from the products can be conveniently carried out by simple filtration. The F-626 filtrates containing the Pd catalyst can be recycled.
A low viscosity ionic liquid [bmim]NTf2 was successfully used as a reaction medium in Pd-catalyzed Mizoroki-Heck, Suzuki-Miyaura and Stille coupling reactions. The yields are good to high, and comparable to those reported previously for high viscosity ionic liquids, such as [bmim]PF6 and [bmim]BF4. The products are readily separated and a reaction medium containing the Pd-carbene catalyst was successfully recycled.
A photochemical [2+2] cycloaddition reaction was executed in a microflow system using glass-made microchannels having 1000-μm width and 500-μm depth. The reaction of cyclohexenones with vinyl acetates in a microflow system under irradiation (300 W, Hg lamp) gave [2+2] cycloaddition products in good yield with a residence time of 2 h, which is a remarkably shortened reaction time compared with a batch system using the same light source.
The deoximation of a variety of α,α′-dioxo-type oximes and oxime ethers was achieved under mild conditions using zinc/AcOH, which gave good yields of α,β-diketo esters.
A continuous microflow system was developed with efficient catalyst recycling for a Mizoroki−Heck reaction of iodobenzene with butyl acrylate, using a low-viscosity ionic liquid ([bmim]NTf2) as the reaction medium. Using a CPC CYTOS Lab System as the microreaction apparatus, in combination with an originally developed microextraction/catalyst recycling system, the reaction medium, which contained Pd catalyst could be continuously recycled to provide a total of 115.3 g (80%, 10 g/h) of the desired product.
The radical carbonylation of 1,5-enynes 1a and 1b using TTMSS as radical mediator gave the predicted carbonylative cyclization products 2a and 2b, respectively, in poor yields. The isolation and characterization of reaction byproducts by X-ray crystallographic analysis suggest that the poor chain propagation can be attributed to the formation of long-lived 3-silyl-1-siloxyallyl radicals, produced by the addition of a (TMS)3Si radical onto the O–C double bond of the initially formed cyclopentanones.