RESUMO
Perfluoroalkyl iodides generally formed electron donor-acceptor (EDA) complexes by halogen bonding with a nitrogen atom containing Lewis bases. Since the electronegativity of the oxygen atom is stronger than that of the nitrogen atom, the resulting Rf-I···O-type halogen bonding EDA complex is less inclined to undergo electron transfer. Here, we reported rare ternary EDA complexes among perfluoroalkyl iodide, oxygen atom, and base. Mechanism experiments and density functional theory theoretical (DFT) calculations indicated that a base-promoted proton-coupled electron transfer (PCET) process was involved in this photochemical reaction. The intracomplex electron transfer event generated two radical species, perfluoroalkyl radical and TEMPO radical, enabling the subsequent oxy-perfluoroalkylation of olefins.
RESUMO
The water-mediated tosylation of alkenes with tosyl cyanide was discovered. Experimental investigations revealed that the reaction was initiated by the in situ formation of sulfinyl sulfone in the presence of water. The sulfinyl sulfone species decomposed to a sulfonyl radical and a sulfinyl radical through homolytic fission. The vinyl sulfone was afforded via sequential addition of the alkene to the sulfonyl radical and the sulfinyl radical, followed by ß-elimination of a sulfinyl moiety.
Assuntos
Alcenos , Água , Cianetos , SulfonasRESUMO
A strategy for photochemical oxidative cleavage of the aminomethylene group at the C2 position of indole was developed to synthesize C2-carbonyl indoles. The reaction was initiated by the photochemical oxidation of N1, followed by a water-assisted concerted H-shift by abstracting hydrogen from aminomethylene. Bromopyridine was discovered to play dual roles as an oxidant for the regeneration of photocatalysts and as an accelerant for the single-electron transfer process.
Assuntos
Indóis , Luz , Catálise , Oxirredução , Estresse OxidativoRESUMO
A photochemical protocol that couples diarylamines and α-ketoesters to afford the chiral 3-hydroxyoxindoles through tandem photoredox and chiral phosphoric acid catalysis is developed. The reaction involves an enantioselective photochemical radical-radical cross-coupling process. The chiral phosphoric acid is discovered to play crucial roles by decreasing the reductive potentials of α-ketoesters and stereocontrolling the downstream asymmetric radical-radical cross-coupling via the formation of pentacoordinate complex.
RESUMO
Thiophenol was discovered to form an EDA complex with iodobenzene through halogen bonding interactions upon treatment with KOH. A direct photochemical thiolation of C(sp3)-H bond-containing etheric, allylic, and benzylic substrates with thiophenol was developed. The reaction proceeded on the basis of the in situ generation of a thiyl radical and aryl radical through single electron transfer between the photoexcited thiophenolate anion and aryl iodide EDA complex. Then a C(sp3) centred-radical was formed by aryl radical-mediated hydrogen atom transfer and the thiolation products were delivered via a radical-radical cross-coupling with the thiyl radical.
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[This corrects the article DOI: 10.1039/D1SC03667J.].
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A three-component Minisci reaction coupling of 1,3-dicarbonyl compounds with vinyl ethers and quinolines or isoquinolines under visible light is developed. The 1,3-dicarbonyl compound undergoes single-electron oxidation to afford an electrophilic 1,3-dicarbonyl radical under visible light irradiation. Due to the polarity of the free radical, the electrophilic radical adds to the electron-rich olefin to afford the nucleophilic radical. It coupled with the heteroarene to afford the three-component coupling products.
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Disclosed herein is a photochemical Heck-type arylation of vinylphenols with non-activated aryl and heteroaryl halides under visible light irradiation. Preliminary mechanistic studies suggested that the colored vinylphenolate anions acted as a strong reducing photoactivator to directly activate (hetero)aryl halides without the need for any sacrificial reductants. The photochemically generated aryl radicals coupled with another molecule of vinylphenol to afford the Heck-type arylation product in a regiospecific and stereoselective manner. The developed photochemical arylation protocol showed exceptional functional group tolerance and was successfully applied in the challenging late-stage modification of natural products without any protection-deprotection procedures.
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An operationally simple photochemical strategy for the direct arylation of oxindoles with (hetero)aryl halides in the absence of both transition metals and photoredox catalysts has been developed. The reaction provides an efficient way to construct various 3-aryloxindole building blocks of pharmaceutical interest at ambient temperature by using household compact fluorescent light (CFL) bulbs as the light source. Preliminarily, mechanistic studies revealed that the intermolecular electron transfer relied on the formation of photon-absorbing electron-donor-acceptor (EDA) complexes between electron-rich oxindole enolates and electron-deficient (hetero)aryl halides, and a radical chain mechanism was operative.
RESUMO
The structural features Kopsia alkaloids, in particular multiple all-carbon quaternary stereocenters in a caged and strained polycyclic skeleton, poses particular challenges for enantioselective total synthesis. Herein, we reported the first total synthesis of (+)-flavisiamineâ F. The synthetic approach involved a room-temperature Overman rearrangement for introducing the chiral amine at C21, a TMS-promoted ketal Claisen rearrangement for constructing the all-carbon quaternary stereocenter at C20, and a late-stage visible-light-induced photochemical cyclization for establishing the all-carbon quaternary stereocenter at C7.
Assuntos
Luz , Aminas/química , Ciclização , Estrutura Molecular , Processos Fotoquímicos , EstereoisomerismoRESUMO
Nitroxides can absorb both ultraviolet (UV) and visible light, and their electron can be excited from the π-bonding orbital to the antibonding π* orbital or the n-bonding orbital to the antibonding π* orbital, respectively. Despite the reported UV-induced hydrogen atom transfer (HAT) process, the potential of nitroxides for visible light-excited photosynthesis is underexplored. Here we demonstrate that nitroxide can convert indole to its radical through a visible light-induced HAT process. A chiral phosphoric acid-catalyzed cyclization of the in situ-formed imine radical, followed by trapping by another molecule of nitroxide, provides the product in high yield and enantioselectivity. To highlight the novelty and efficiency of this strategy, an asymmetric total synthesis of natural product (-)-verrupyrroloindoline was accomplished in 5 steps.
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A concise total synthesis of (±)-serotobenine via a strategy inspired by the biosynthetic hypothesis for this alkaloid was accomplished. The indolofuran core was constructed by an iron-catalyzed intermolecular oxidative radical cross-coupling reaction developed by our group.
Assuntos
Indóis/química , Indóis/síntese química , Catálise , Técnicas de Química Sintética , Ferro/química , EstereoisomerismoRESUMO
A Curtius-like rearrangement of hydroxamates to isocyanates was discovered. This reaction was initiated from an iron(II)-nitrenoid complex, which was generated by the iron(II)-catalyzed cleavage of N-O bonds of functionalized hydroxamates. To demonstrate the efficiency of this new Curtius-like rearrangement in synthetic chemistry, a biomimetic strategy for the one-pot preparation of bisindolylmethanes was developed.
Assuntos
Materiais Biomiméticos/síntese química , Compostos Ferrosos/química , Indóis/síntese química , Metano/síntese química , Materiais Biomiméticos/química , Catálise , Indóis/química , Metano/análogos & derivados , Metano/química , Estrutura MolecularRESUMO
An iron-catalyzed oxidative radical coupling reaction was developed to selectively construct indolofuran or bisphenolic indole cores, which exist in two types of moschamine-related indole alkaloids. Both (+)-decursivine and 4,4â³-bis(N-feruloyl)serotonin were biomimetically synthesized by using coupling reactions. The proposed reassignment of the structure of montamine as 4,4â³-bis(N-feruloyl)serotonin was excluded.
Assuntos
Alcaloides Indólicos/síntese química , Ferro/química , Biomimética , Catálise , Alcaloides Indólicos/química , Estrutura Molecular , Acoplamento Oxidativo , Serotonina/análogos & derivados , EstereoisomerismoRESUMO
Facile, straightforward, and asymmetric total syntheses of (+)-chimonanthine (1), (+)-folicanthine (2), and (-)-calycanthine (3) were accomplished in four to five steps from commercially available tryptamine. The synthesis features copper-mediated asymmetric cyclodimerization of chiral tryptamine derivative, which established a new entry into constructing the sterically hindered vicinal quaternary stereogenic carbon centers of dimeric hexahydropyrroloindole alkaloids in one procedure. An unprecedented base-induced isomerization from the chimonanthine skeleton to the calycanthine skeleton was observed and facilitated the synthesis of (-)-calycanthine (3).
Assuntos
Alcaloides Indólicos/química , Indóis/síntese química , Naftiridinas/síntese química , Pirróis/síntese química , Catálise , Indóis/química , Estrutura Molecular , Naftiridinas/química , Pirróis/química , EstereoisomerismoRESUMO
A copper-mediated cyclization and dimerization of tryptamine or tryptophan was developed to generate a C2-symmetry C3(sp(3))-C3(sp(3)) bridge with two contiguous stereogenic quaternary carbons in one step. Impressively, the ratio between exo and endo cyclization products varies when different protecting groups of Nb are utilized. This dimerization reaction could be conducted in gram scale. With this dimerization method, both endocyclotryptophan (+)-WIN 64821 and exocyclotryptophan (-)-ditryptophenaline were synthesized in 5 steps.
Assuntos
Cobre/química , Indóis/química , Indóis/síntese química , Piperazinas/síntese química , Pirróis/química , Pirróis/síntese química , Triptaminas/química , Triptofano/química , Ciclização , Dimerização , Estrutura Molecular , Piperazinas/química , EstereoisomerismoRESUMO
An unprecedented copper-catalyzed intramolecular radical cyclization was developed for the synthesis of 3-hydroxypyrroloindoline skeletons in excellent yields. The 3-hydroxyl group was introduced by trapping the radical intermediate with molecular oxygen or TEMPO. This process represents a unique radical oxidation pathway for tryptamine/tryptophan derivatives and allows a rapid biomimetic synthesis of natural product protubonine A.
Assuntos
Alcaloides/síntese química , Cobre/química , Dicetopiperazinas/síntese química , Alcaloides/química , Biomimética , Catálise , Ciclização , Dicetopiperazinas/química , Indóis/síntese química , Estrutura Molecular , Oxirredução , Estereoisomerismo , TriptofanoRESUMO
Plasmalogen lysophosphatidylethanolamine (pLPE) had been identified as a self antigen for natural killer T cells (NKT cells). It is very important in the development, maturation and activation of NKT cells in thymus. Besides, pLPE is a novel type of antigen for NKT cells. To evaluate the structure-activity relationship (SAR) of this new antigen, pLPE and its analogues referred to different aliphatic chains and linkages at the sn-1 position of the glycerol backbone were synthesized, and the biological activities of these analogues was characterized. It is discovered that the linkages between phosphate and lipid moiety are not important for the antigens' activities. The pLPE analogues 1, 3, 4, 7 and 9, which have additional double bonds on lipid parts, were identified as new NKT agonists. Moreover, the analogues 4, 7 and 9 were discovered as potent Th2 activators for NKT cells.