A novel copper‐catalyzed selective semihydrogenation of terminal alkynes using hypophosphorous acid as hydrogen donor took place efficiently to afford the corresponding alkenes in high yields. A broad range of substituted terminal aromatic and aliphatic alkenes, including terminal dienes and enynes bearing internal triple bonds, can be efficiently synthesized by this reaction.
We have developed an electrophilic addition of allylic carbocations to 2‐cyclopropylidene‐2‐arylethanols constructing carbon‐carbon bonds with excellent regio‐ and stereoselectivities. The reaction affords 3‐oxabicyclo[3.2.0]heptanes in moderate to good yields via the electrophilic addition/ring‐opening/vinyl group shift/intramolecular cyclization sequence.
1,1,1‐Trifluoroacetone tosylhydrazone is presented as a very convenient substrate for the palladium‐catalyzed cross‐coupling with aryl halides. Under the proper reaction conditions, 3,3,3‐trifluoromethylstyrenes – very valuable trifluoromethylated synthetic intermediates – are obtained with high yields. The reaction features a very wide scope, as the presence of most functional groups is tolerated. Moreover, the reaction has been extended to substituted trifluoromethylstyrenes by employing substituted tosylhydrazones derived from other trifluoromethyl ketones.
A method for copper‐catalyzed aryltrifluoromethylation of N‐phenylcinnamamides is reported. This method provides a straightforward route to a variety of CF3‐containing 3,4‐dihydroquinolin‐2(1 H)‐ones with excellent regioselectivity and diastereoselectivity.
The visible light‐induced iodine‐catalyzed oxidative cleavage of the CC bond for transforming terminal alkynes into primary amides in the presence of ammonia under aqueous conditions is described. This metal‐free protocol which ensued via initial hydroamination of the acetylene bond followed by liberation of diiodomethane (CH2I2) was found to be applicable to aromatic, heteroaromatic and aliphatic alkynes.
A new, non‐symmetrical copper(II) pincer complex catalyzes much more efficiently the formation of benzofuran by the reaction between ortho‐iodophenols and alkynes. The lowest catalyst loadings are realized for this reaction, and bromo‐ and chlorophenols are heteroannulated for the first time. Strong evidence for hydrophenoxylation and intramolecular halogen atom‐transfer steps catalyzed by this remarkably active, recyclable homogeneous catalyst is provided.
A new rhodium(III)‐catalyzed N‐annulation reaction of benzylamines with internal alkynes has been developed. Observations made during these efforts suggest that the mechanistic pathway followed in this process involves direct participation of benzylamines without their preliminary oxidative dehydrogenation. Moreover, N‐annulation reactions of primary benzylamines result in the formation of mixtures of isoquinolines and 8‐vinylisoquinolines. Finally, secondary and tertiary benzylamines undergo rhodium(III)‐catalyzed N‐annulation reactions to generate the respective isoquinolinium and hydroisoquinolinium salt products.
A straightforward assisted tandem palladium(II)‐ and palladium(0)‐catalyzed direct C‐3 and N‐4 arylation of quinoxalin‐2(1 H)‐ones with boronic acids and aryl halides in water as safe and cheap solvent is reported. This environmentally friendly catalytic protocol is compatible with a wide range of functional groups and allows construction of various biologically important quinoxalin‐2(1 H)‐one backbones.
For the synthesis of multisubstituted dispirocyclohexane derivatives, a Rauhut–Currier‐initiated organocascade reaction between 2‐arylideneindan‐1,3‐diones and activated alkenes in the presence of diazabicyclo[2.2.2]octane (DABCO) was demonstrated. The functionalized dispirocyclohexanes with a wide range of substituents were obtained in satisfactory to excellent chemical yields (58–99%) with high chemo‐ and diastereoselectivities (>95:5 dr). This organocatalytic reaction proceeded smoothly through Michael/Michael cyclization, which involves the formation of three new carbon‐carbon bonds with simultaneous construction of two all‐carbon spiro quaternary centers.
Visible light and eosin Y catalyze the synthesis of vinyl sulfones from aryl sulfinates and alkenes by a photoredox process. The reaction scope is broad in aryl sulfinates and alkenes and the general and simple procedure provides a metal‐free alternative for the synthesis of synthetically valuable vinyl sulfones.
The palladium‐catalyzed acylation of 2‐aryl‐1,2,3‐triazoles with aldehydes via C H bond activation is described. A wide variety of products was isolated in good to excellent yields. This finding provides a new and useful strategy for the synthesis of aromatic ketones.
A simple but efficient organocatalytic system with 5 mol% tetra‐n‐butylammonium bromide (TBAB) as the catalyst has been identified for alcohol oxidation for the first time. This organocatalytic system is compatible with a broad range of benzylic/allylic alcohols with various catalytically reactive groups. Besides, it shows excellent selectivity for secondary benzylic alcohols over aliphatic alcohols, and good selectivity over the primary benzylic alcohol site in 4‐(1‐hydroxyethyl)benzyl alcohol. Thus, the features of simplicity, high efficiency, selectivity and mildness of reaction conditions associated with this TBAB organocatalytic system suggest its potential for widespread use in synthetic chemistry.
The rhodium(III)‐catalyzed aromatic C H activation/intramolecular Heck‐type reaction has been studied to synthesize spirocyclic compounds, an important class of molecules in medicinal chemistry and natural product synthesis. This approach was efficient with a variety of substituted N‐methoxybenzamides tethered to different cyclic alkenes having a 5‐, 6‐ or 7‐membered ring. This practical method affords sterically hindered o‐substituted aryl spirocycles that are valuable compounds for further functionalization to access relevant building blocks.
A general, selective and extremely efficient procedure for the aerobic cleavage of aromatic alkenes is presented. TON values in the range 6,000,000–10,000,000 are obtained for this nickel‐catalyzed reaction performed in polyethylene glycol 400 under 1 atm of molecular oxygen. Mono‐, di‐, tri‐ and tetrasubstituted styrene derivatives are oxidatively cleaved by this reproducible protocol, also suitable for larger scale (1.5 g) reactions. The presence of several functional groups (alkyl, alkoxy, halogen, trifluoromethyl) is tolerated in the substrates. The mechanistic proposal to explain the selective generation of carboxylic acids and ketones from aromatic alkenes involves the participation of the polyol solvent in the presented oxidative process.
This paper describes the aerobic oxidation of styrenes catalyzed by iron(III) chloride (FeCl3) to form β‐keto‐N‐alkoxyphthalimides in fair to good yields. This oxidative process employs mild conditions with green and atom efficient dioxygen (O2) as the oxidant.
A gold(I)‐catalyzed cascade [3,3]‐propargylic rearrangement and [4+2] cycloaddition reaction of 2‐vinylindoles with propargylic esters is reported. The reaction leads to the synthesis of highly substituted tetrahydrocarbazole derivatives in high yields and diasteroselectivities. Furthermore, a preliminary screening for an asymmetric version of this reaction is described.
The pyrrolo[3,2,1‐ij]quinoline heterocyclic core is found in the structure of a variety of compounds with interesting applications and then, new efficient and flexible strategies to construct this skeleton are required. Here, a new diastereoselective tetrafluoroboric acid (HBF4)‐catalyzed three‐component coupling reaction of 1H‐indole‐7‐carbaldehyde derivatives, anilines and electron‐rich alkenes to give pyrrolo[3,2,1‐ij]quinolines is described. The reaction involves an unusual [4+2]‐heterocyclization between an in situ formed imine and an alkene. The new catalytic method, where water is the only by‐product, is efficient, robust and flexible, and allows for multigram‐scale synthesis.
A direct cyanation of benzyl ethers and 1,3‐diarylpropenes with TMSCN was performed under solvent‐ and metal‐free conditions. This oxidative cross dehydrative coupling (CDC) reaction was promoted by 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and provided rapid access to a broad range of nitriles in good to excellent yields.
