Rh(III)-catalyzed tandem oxidative olefination-Michael reactions between aryl carboxamides and alkenes

Rh(III)-catalyzed oxidative coupling reactions between benzamides or heteroaryl carboxamides and olefins have been developed. The vinylation product can further undergo a Michael reaction leading to γ-lactam in the case of electron-withdrawing olefins.     

Selective preparation of terminal alkenes from aliphatic carboxylic acids by a palladium-catalysed decarbonylation-elimination reaction

Trialkylamines were used as additives in the decarbonylation-elimination reaction catalysed by the combination of palladium(II) chloride and DPE-Phos. Aliphatic carboxylic acids were transformed at relatively low temperature into terminal alkenes in high yield and high selectivity, without the need for distillation, thereby avoiding isomerisation.     

Regioselective cross-coupling of allylindium reagents with activated benzylic bromides—a simple and efficient procedure for the synthesis of terminal alkenes

Allylindium reagents undergo facile and highly regioselective cross-coupling with benzylic and cinnamyl bromides in THF at room temperature without any catalyst producing terminal alkenes in high yields. The addition is highly regioselective and is found to provide γ-adducts in all reactions.     

Regioselective aminobromination of terminal alkenes

The addition of t-butyl N,N-dibromocarbamate (BBC) to a variety of terminal alkenes has been studied. The reaction was spontaneously initiated and proceeded smoothly in refluxing dichloromethane. The N-bromo adducts, formed upon addition, could be reduced in situ with aqueous sodium sulfite to give the corresponding 2-bromo-N-Boc-amines. Immediate deprotection of these compounds with gaseous HCl or p-toluenesulfonic acid afforded 2-bromoamine hydrochlorides or tosylates in pure state and good overall yields. The observed regioselectivity for anti-Markovnikov addition, as proven by NMR and MS, is fully consistent with the radical-chain mechanism proposed for the reaction.     

CuI-catalyzed tandem synthesis of thioethers using aryl halides,electron-deficient alkenes,and sodium iso-propyl xanthogenate

A ligand-free, CuI-catalyzed protocol was developed for the one-step preparation of Michael adducts of aromatic thiols in high yields by reacting a mixture of an aryl halide and an electron-deficient alkene with sodium iso-propyl xanthogenate.     

Iron-mediated and -catalyzed metalative cyclization of electron-withdrawing-group-substituted alkynes and alkenes with Grignard reagents

Treatment of ethyl (E)‐5,5‐bis[(benzyloxy)methyl]‐8‐(N,N‐diethylcarbamoyl)‐2‐octen‐7‐ynoate with an iron reagent generated from FeCl₂ and tBuMgCl in a ratio of 1:4 (abbreviated as FeCl₂/4 tBuMgCl) afforded ethyl [4,4‐bis[(benzyloxy)methyl]‐2‐[(E)‐(N,N‐diethylcarbamoyl)methylene]cyclopent‐1‐yl]acetate in good yield. Deuteriolysis of an identical reaction mixture afforded the bis‐deuterated product ethyl [4,4‐bis[(benzyloxy)methyl]‐2‐[(E)‐(N,N‐diethylcarbamoyl)deuteriomethylene]cyclopent‐1‐yl]deuterioacetate, thus confirming the existence of the corresponding dimetalated intermediate. The latter intermediate can react with halogens or aldehydes to facilitate further synthetic transformations. The amount of FeCl₂ was reduced to catalytic levels (10 mol % relative to enyne), and catalytic cyclizations of this sort proceeded with yields comparable to those of the aforementioned stoichiometric reactions. The cyclization of diethyl (E,E)‐2,7‐nonadienedioate with a stoichiometric amount of FeCl₂/4 tBuMgCl, followed by the addition of sBuOH as a proton source, afforded a mixture of 2‐(ethoxycarbonyl)‐3‐bicyclo[3.3.0]octanone and its enol form in good yield. The use of aldehyde or ketone in place of sBuOH afforded 2‐(ethoxycarbonyl)‐3‐bicyclo[3.3.0]octanone, which has an additional hydroxyalkyl side chain. Additionally, the metalation of a carbon–carbon unsaturated bond in N,N‐diethyl‐5,5‐bis[(benzyloxy)methyl]‐7,8‐epoxy‐2‐octynamide or (E)‐3,3‐dimethyl‐6‐(N,N‐diethylcarbamoyl)‐5‐hexenyl p‐toluenesulfonate with FeCl₂/4 tBuMgCl or FeCl₂/4 PhMgBr was followed by an intramolecular alkylation with an epoxide or alkyl p‐toluenesulfonate to afford 5,5‐bis[(benzyloxy)methyl]‐3‐[(E)‐(N,N‐diethylcarbamoyl)methylene]‐1‐cyclohexanol or N,N‐diethyl(3,3‐dimethylcyclopentyl)acetamide after hydrolysis. In both cases, the remaining metalated portion α to the amide group was confirmed by deuteriolysis and could be utilized for an alkylation with methyl iodide.     

Formation of isomeric iodohydrins from terminal alkenes upon oxidation by a RuCl3-NaIO4 system

RuCl₃-catalyzed periodate oxidation of alkenes affords isomeric iodohydrins.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2961–2963, December, 1996.     

Copper(I)-catalyzed arylselenylation of aryl bromides and iodides

A new protocol to prepare unsymmetrical diarylselenides using the reaction of aryl bromides and iodides with easily available Bu₃SnSeAr catalyzed by Cu(I) complexes under rather mild conditions and with a very high yield is described.     

Palladium-catalyzed heteroannulation of cyclic alkenes by functionally substituted aryl iodides

Indolines and 2,3-dihydrobenzofurans are produced in good yields by the Pd(0)-catalyzed heteroannulation of cyclic and bicyclic alkenes by o-amino- and o-hydroxyaryl iodides. These processes are only successful with cyclic olefins in which the key alkylpalladium intermediate cannot undergo facile palladium β-hydride elimination. These reactions appear to involve: (1) oxidative addition of the aryl iodide to the palladium catalyst, (2) arylpalladation of the olefin, (3) possible coordination of the internal nucleophile to the palladium, (4) formation of a six-membered palladacycle, and (5) reductive elimination of the organopalladium intermediate to give the heteroannulation product and regenerate Pd(0).     

Hydroalumination of alkenes by the LiAlH4 · 3AlBr3 system

The hydroalumination of a series of alkenes and some fused aromatic hydrocarbons by the LiAlH₄ · 3AlBr₃ system in low-polar solvents was studied. Alkenes with mono-, di-, tri-, and tetraalkyl substituted, mono- and diaryl substituted double bonds and anthracene react at room temperature to give the corresponding dibromoaluminoalkanes in high yields. Benzylidenefluorene, tetraphenylethylene, naphthalene, and phenanthrene do not undergo hydroalumination under these conditions. Camphene, bicyclo[3.2.1]oct-2-ene, and norbornene afford the corresponding organoaluminum compounds with high stereoselectivity. Oxidation and halo- and acyldemetallation of the resulting alkyl- and arylalanes were carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1637–1642, September, 1993.     

An unexpected Lewis acids-catalyzed tandem ring-opening rearrangement of vinylcyclopropane ketone with aryl aldehyde

A novel tandem reaction of vinylcyclopropane ketone with benzaldehyde has been successfully developed. This provides a new method for the preparation of γ-oxo-hexenone derivatives from easily accessible starting materials.     

Sulfamic acid: An efficient and recyclable catalyst for the regioselective hydrothiolation of terminal alkenes and alkynes with thiols

Herein, we described a new method for the preparation of thioethers through hydrothiolation of alkenes and alkynes, using sulfamic acid as a reusable catalyst. Generally, this new methodology afforded the desired products in very good yields, under metal and solvent-free conditions. Furthermore, the catalyst was easily recovered and reused for further catalytic reactions without loss of activity.     

Cross-coupling of aryl iodides with paramagnetic terminal acetylenes derived from 4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide

2-(Arylylethynylphenyl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxides 12 and 13 were synthesized by cross-coupling of aryl iodides with 1-alkynes containing the 4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide fragment. A procedure was developed for the preparation of 3- and 4-ethynylbenzaldehydes with the use of 2-methylbut-3-yn-2-ol.     

Palladium-induced electron-transfer reaction of difluorodiiodomethane with alkenes

The addition reaction of difluorodiiodomethane (1) with alkenes in the presence of PdCl2(PPh3)2 or Pd(PPh3)4 afforded the corresponding iododifluoromethylated compounds in excellent yield.     

Efficient copper-free PdCl2(PCy3)2-catalyzed Sonogashira coupling of aryl chlorides with terminal alkynes

Under copper-free conditions and with Cs2CO3 as a base, PdCl2(PCy3)2 showed high catalytic activity for cross-coupling of electron-rich, electron-neutral, and electron-deficient aryl chlorides with a variety of terminal alkynes in DMSO at 100-120 degrees C affording internal arylated alkynes in good to excellent yields.