RESUMEN
The photoinduced regioselective HAT reactions of acetals, ethers, and alcohols using benzoic acids in a two-molecule photoredox system led to the formation of new C-C bonds with alkenes under mild conditions. Aryl carboxy radicals generated from benzoic acids in a two-molecule photoredox system can function as catalytic HAT reagents, even though an excess amount of a hydrogen donor substrate is required. Various acetals, ethers, alcohols, and alkenes can be employed in the photoreaction to provide both high yields of adducts and high recoveries of benzoic acids.
RESUMEN
Using our recent relevant results, this account shows the featured reactivities of two-molecule photoredox systems compared to one-molecule photoredox systems. The low efficiency of electron transfer processes, such as photoinduced and back-electron transfer, in the two-molecule photoredox system, furnishes unique products through different pathways. The facile replacement of photoredox catalysts with appropriate oxidation/reduction potentials in this system provides valuable insights into photoredox reactions.
RESUMEN
Double difunctionalization of a vinyl ether tethered hydroxy or carbamoyl group with electron-deficient alkenes such as acrylonitrile or acrylic esters was achieved by visible-light irradiation in a two-molecule photoredox system. Use of anhydrous acetonitrile solution as a solvent promoted both dimerization of the radical cation of electron-rich alkene with electron-rich alkene and intramolecular nucleophilic addition to generate an electron-rich radical that was added to electron-deficient alkene to furnish the double difunctionalized product. A variety of electronically differentiated rich and deficient alkenes were used in the photoreaction; a simple construction of a complex carbon framework containing acetal from simple alkenes was successful under mild conditions.
RESUMEN
The side-chain functionalization of aspartic/glutamic acid derivatives through photoinduced decarboxylation was achieved by using organic two-molecule photoredox catalysts without racemization under mild conditions. A facile process involving the preparation of substrates and photoinduced decarboxylative radical additions can provide easy access to the linked amino acids with carbohydrates and amino acids at the side chain.
Asunto(s)
Glutamatos , Procesos Fotoquímicos , Aminoácidos/química , Estructura Molecular , Oxidación-ReducciónRESUMEN
Visible-light-induced decarboxylative and deboronative reactions using two-molecule organic photoredox catalysts, namely, phenanthrene (Phen) and biphenyl (BP), as electron donors and 9-cyano-10-methoxycarbonylanthracene 1a as an electron acceptor were achieved. The high solubility of 1a significantly improved the reaction efficiency and product yield. In addition, the facile tuning of the oxidation potential of the electron-donor molecule via the replacement of Phen with BP enabled the application of the two-molecule photoredox system to a wide range of substrates.
RESUMEN
Photoinduced decarboxylative radical reactions of benzoic acids with electron-deficient alkenes, diborane, and acetonitrile under organic photoredox catalysis conditions and mild heating afforded adducts, arylboronate esters, and the reduction product, respectively. The reaction is thought to involve single-electron transfer promoted the generation of aryl radicals via decarboxylation. A diverse range of benzoic acids were found to be suitable substrates for this photoreaction. Only our two-molecule organic photoredox system can work well for the direct photoinduced decarboxylation of benzoic acids.
RESUMEN
Sequential radical addition to alkenes and reductive radical cyclization of phenylalanine and tyrosine derivatives via photoinduced decarboxylation furnished ring-constrained γ-amino acids under mild conditions. A variety of alkenes such as acrylamides and acrylic esters could be employed in the photoinduced radical cascade cyclization. The yields of the ring-constrained γ-amino acids are dependent on the electron-accepting ability and steric hindrance of the alkene used. The proposed sequential reaction can also be applied for direct tethering of dipeptides to yield unique ring-constrained tetrapeptides.
RESUMEN
A new strategy for the synthesis of 23-, 25-, 27-, and 29-membered ( Z)-selective unsaturated and saturated macrocyclic lactones from commercially available 16- and 17-membered macrocyclic lactones and bromoalcohols by Wittig reaction, Yamaguchi macrolactonization, and photoinduced decarboxylative radical macrolactonization is described. The position of the unsaturated part in the macrocyclic lactones can be controlled by changing the number of carbons in the starting materials. This protocol can provide facile access to the desired large-ring ( Z)-selective unsaturated and saturated macrocyclic lactones from simple starting materials.
RESUMEN
Directly linked donor and acceptor arenes, such as phenanthrene/naphthalene/biphenyl and 1,3-dicyanobenzene were found to work as photoredox catalysts in the photoreactions of indene, 2,3-dimethyl-2-butene, and 4-methoxyphenylacetic acid. The new stable organic photocatalyst forms an intramolecular exciplex (excited complex) when irradiated in a polar solvent and shows redox catalyst activity, even at low concentrations. To the best of our knowledge, this is the first example of an intramolecular exciplex working as a redox catalyst.
Asunto(s)
Naftalenos/química , Nitrilos/química , Fenantrenos/química , Procesos Fotoquímicos , Catálisis , Oxidación-ReducciónRESUMEN
O-Alkylations of serine and threonine derivatives at the hydroxy group were achieved using photoinduced decarboxylative radical reactions of serinyl and threoninyl acetic acids with an organic photocatalyst without racemization under mild conditions. Photoinduced decarboxylative radical additions of serinyl and threoninyl acetic acids to electron-deficient alkenes provided linked serine and threonine with carbohydrates and amino acids at the side chain. In addition, O-methylations containing deuterium and O-benzylation of serine were performed under similar photochemical conditions.
RESUMEN
Two types of photoreactions between electronically differentiated donor and acceptor alkenes assisted by nucleophilic addition using an organic photoredox catalyst efficiently afforded 1:1 or 2:1 cross-coupling adducts. A variety of alkenes and alcohols were employed in the photoreaction. Control of the reaction pathway (i.e., the formation of the 1:1 or 2:1 adduct) was achieved by varying the concentration of the alcohol used. Detailed mechanistic studies suggested that the organic photoredox catalyst acts as an effective electron mediator to promote the formation of the cross-coupling adducts.
RESUMEN
The facile alkylative intramolecular cyclization of 3-alkoxycarbonyl-2-oxopropyldiphenylsulfonium salts is described. This simple method can be readily applied to the synthesis of a novel family of 4-alkylated 3(2H)-furanones in moderate to high yields under mild conditions via a one-pot process.
RESUMEN
Proteinogenic amino acid residues that promote ß-sheet secondary structure are hydrophobic (e.g., Ile or Val) or only moderately polar (e.g., Thr). The design of peptides intended to display ß-sheet secondary structure in water typically requires one set of residues to ensure conformational stability and an orthogonal set, with charged side chains, to ensure aqueous solubility and discourage self-association. Here we describe new amino acids that manifest substantial ß-sheet propensity, by virtue of ß-branching, and also bear an ionizable group in the side chain.
Asunto(s)
Aminoácidos/química , Péptidos/química , Interacciones Hidrofóbicas e Hidrofílicas , Modelos Moleculares , Conformación Molecular , Péptidos/síntesis química , Estructura Secundaria de Proteína , SolubilidadRESUMEN
We developed a rhodium-catalyzed chain-walking hydrothiolation process for internal alkenes, which offers a novel and efficient alternative for C(sp3)-H bond cleavage, while focusing on thiol incorporation. This method exclusively affords N,S-acetals at 36-90% yields. Regioconvergent hydrothiolation significantly improved the effectiveness of this transformation. Preliminary mechanistic investigations revealed that an amide-directing group is essential for regioselective synthesis, underlining its significance in this process.
RESUMEN
A new method for the synthesis of macrocyclic lactones, lactams, and ketones, which utilizes photoinduced intramolecular radical cyclization reactions of substrates containing tethered carboxylic acids and α,ß-unsaturated carbonyl moieties, has been uncovered. Photocyclization of the carboxylic acids tethered acrylate ester, which were prepared starting from the macrocyclic lactones, gave the two-carbon elongated macrocyclic lactones via decarboxylation. Similar photoreactions of carboxylic acid tethered acryl amide or α,ß-unsaturated ketone moieties, which were also prepared starting from the macrocyclic lactones, produced macrocyclic lactams or ketones, respectively. The simple approach can be readily applied to the preparation of a variety of macrocyclic lactones, lactams, and ketones with tunable ring sizes.
Asunto(s)
Ácidos Carboxílicos/química , Cetonas/química , Cetonas/síntesis química , Lactamas Macrocíclicas/química , Lactamas Macrocíclicas/síntesis química , Lactonas/química , Lactonas/síntesis química , Catálisis , Ciclización , Estructura Molecular , FotoquímicaRESUMEN
Single electron transfer (SET)-photochemical decarboxylation of free carboxylic acids was performed in a polar solvent using several arenes such as phenanthrene, naphthalene, 1-methylnaphthalene, biphenyl, triphenylene, and chrysene in the presence of various electron acceptors such as 1,2-, 1,3-, and 1,4-dicyanobenzenes, methyl 4-cyanobenzoate, and 1,4-dicyanonaphthalene. The decarboxylation reaction was influenced by the arenes, electron acceptors, and solvent. The best result was achieved by the photoreaction using biphenyl and 1,4-dicyanonaphthalene in aqueous acetonitrile.
Asunto(s)
Ácidos Carboxílicos/química , Solventes/química , Acetonitrilos/química , Compuestos de Bifenilo/química , Crisenos/química , Cianuros/química , Descarboxilación , Transporte de Electrón , Naftalenos/química , Fenantrenos/química , Procesos FotoquímicosRESUMEN
The decarboxylation of free carboxylic acids was effected by a photogenerated cation radical of phenanthrene to yield the reduction product in the presence of a thiol, which provides an alternative method to the Barton decarboxylation procedure for aliphatic acids such as N-Boc amino acids.
Asunto(s)
Ácidos Carboxílicos/química , Ácidos Carboxílicos/efectos de la radiación , Compuestos Orgánicos/síntesis química , Compuestos Orgánicos/efectos de la radiación , Rayos Ultravioleta , Cationes/química , Cationes/efectos de la radiación , Descarboxilación , Radicales Libres/síntesis química , Radicales Libres/química , Radicales Libres/efectos de la radiación , Estructura Molecular , Compuestos Orgánicos/química , Oxidación-Reducción , Fotoquímica , Estereoisomerismo , Compuestos de Sulfhidrilo/químicaRESUMEN
Metal-free photoinduced decarboxylative radical polymerization of aliphatic carboxylic acids with a variety of monomers was found to proceed smoothly to give the corresponding polymers under mild conditions. Complex carboxylic acids such as those of sugars, steroids, and peptides can function as benign radical initiators via decarboxylation and can be incorporated at the polymer chain ends. This synthetic methodology represents a facile introduction of molecules and functionalities to polymers by using commercially available carboxylic acids.
RESUMEN
Photoinduced electron transfer (PET) promoted decarboxylation of α-(ω-carboxyalkyl) ß-keto esters undergoes radical ring expansion and cyclization reactions. This mild and environmentally friendly method can provide one-carbon expanded γ-keto esters and bicyclic alcohols, and the product distribution is strongly dependent on the length of the alkyl chain containing the terminal carboxylate group.
RESUMEN
Deuterium exchange of a carboxy group was achieved by photochemical decarboxylation of free carboxylic acids in the presence of thiol and a small amount of D(2)O, and a deuterated product with excellent deuterium content was obtained; this reaction is a practical means of synthesizing regioselective deuterium-labelled compounds under mild reaction conditions.