- Convenient synthesis of cyclic α-alkoxyl-α,β-unsaturated carboxylic acids by nickel-catalyzed electrochemical carboxylation of lactone enol triflates
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Electrochemical carboxylation of lactone enol triflates in DMF containing a catalytic amount of NiBr2·bpy with a platinum cathode and a magnesium anode under an atmospheric pressure of CO2 gave the corresponding cyclic α-alkoxyl-α,β-
- Senboku,Kanaya,Tokuda
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Read Online
- Iodine-Catalyzed Nazarov Cyclizations
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The Nazarov cyclization is an important pericyclic reaction that allows the synthesis of substituted cyclopentenones. We now demonstrate that this reaction can be performed under very mild, metal-free reaction conditions using molecular iodine as the catalyst. A variety of different divinyl ketones including aromatic systems undergo the iodine-catalyzed reaction with moderate to very good yields in both polar and apolar solvents. Our mechanistic studies indicate that the Nazarov system is activated through a halogen bond between the carbonyl group and the catalyst, and other modes of action like Br?nsted acid or iodonium ion catalysis are unlikely. Furthermore, addition of iodine to the double bond or a putative iodine-catalyzed cis-trans isomerization of the employed olefins seem not to be an important side reaction here.
- Koenig, Jonas J.,Arndt, Thiemo,Gildemeister, Nora,Neud?rfl, J?rg-M.,Breugst, Martin
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p. 7587 - 7605
(2019/06/27)
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- Asymmetric Nazarov Cyclizations Catalyzed by Chiral-at-Metal Complexes
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The application of Lewis acidic chiral-at-metal complexes of iridium(III) and rhodium(III) as catalysts for the asymmetric polarized Nazarov cyclization of dihydropyran- and indole-functionalized α-unsaturated β-ketoesters is reported (overall 24 examples). For both substrate classes, catalyst loadings of 2 mol% were found to be sufficient for achieving high yields and high stereoselectivities. The cyclized dihydropyran products were isolated in 85–98% yield, with 89%–>99% ee, and trans/cis ratios of 15:1–50:1 (9 examples). The cyclized indole products were typically isolated in more than 70% yield and in up to 93% yield, typically with more than 90% ee and in up to 97% ee, and trans/cis ratios of 12:1–28:1 (15 examples). (Figure presented.).
- Mietke, Thomas,Cruchter, Thomas,Larionov, Vladimir A.,Faber, Tabea,Harms, Klaus,Meggers, Eric
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supporting information
p. 2093 - 2100
(2018/04/19)
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- The first calcium-catalysed Nazarov cyclisation
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The first calcium-catalysed Nazarov cyclisation is described. The Ca(NTf2)(PF6) complex is found to be a very active catalyst for 4π electrocyclisations. The remarkable catalytic activity of this complex is attributed to its increased Lewis acidity compared to other Ca complexes. Spectroscopic studies have provided an insight into the chelating interactions between the substrate and the Ca catalyst.
- Davies, Jacob,Leonori, Daniele
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supporting information
p. 15171 - 15174
(2014/12/11)
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- Iridium-catalyzed enantioselective hydrogenation of unsaturated heterocyclic acids
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Spiral binding: A highly enantioselective hydrogenation of unsaturated heterocyclic acids has been developed by using chiral iridium/spirophosphino oxazoline catalysts (see scheme; BArF-=tetrakis[3,5- bis(trifluoromethyl)phenyl]borate, Boc=tert-butoxycarbonyl). This reaction provided an efficient method for the preparation of optically active heterocyclic acids with excellent enantioselectivities. Copyright
- Song, Song,Zhu, Shou-Fei,Pu, Liu-Yang,Zhou, Qi-Lin
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supporting information
p. 6072 - 6075
(2013/07/05)
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- A reductive-coupling plus nazarov cyclization sequence in the asymmetric synthesis of five-membered carbocycles
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Palladium-mediated hydrostannylation of alkynoyl compounds is combined with Stille-Scott cross-coupling (reductive-coupling) to give one-pot access to divinyl and aryl vinyl ketones, which undergo Nazarov cyclization to give cyclopentenones upon treatment with acid. This reaction sequence has been studied with a variety of different substitution patterns, including the use of oxazolidinone auxiliaries to achieve torquoselectivity in the Nazarov cyclization. Through a combination of good yields and moderate to good levels of stereochemical induction, this approach affords efficient, convergent, and asymmetric access to a variety of different cyclopentanoid systems.
- Kerr, Daniel J.,White, Jonathan M.,Flynn, Bernard L.
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supporting information; experimental part
p. 7073 - 7084
(2010/12/25)
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- Synthesis of the core structure of the fungal metabolite benesudon: Use of oxidative decarboxylation
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(Chemical Equation Presented) The core structure (5) of the fungal metabolite benesudon (1) was synthesized, the key step being oxidative decarboxylation of acid 17.
- Clive, Derrick L. J.,Minaruzzaman,Yang, Haikang
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p. 5581 - 5583
(2007/10/03)
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- Preparation of 6-carboxy-3,4-dihydro-2H-pyran
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6-Carboxy-3,4-dihydro-2H-pyran and ring-substituted derivatives thereof are prepared by reacting a 1,4-disubstituted butane having leaving groups at the one and four positions in a liquid solvent medium with carbon monoxide at elevated temperature and pressure in the presence of a catalytic amount of a metal carbonyl compound and an alkali metal inorganic base or an alkaline earth metal inorganic base.
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- One-Pot Preparation of α-Cyanovinyl Ethers (2-Alkoxy-2-alkenenitriles) from Vinyl Ethers: Elaboration to 3-Alkoxy-2-oxo-3-alkenenitriles and Aluminium Chloride-Catalyzed Cycloadditions to Cyclopentadiene
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A variety of α-cyanovinyl ethers have been prepared by 3 different routes and elaborated to 3-alkoxy-2-oxo-3-alkenenitriles.The latter, in the presence of cyclopentadiene and aluminium chloride, give novel bridged 7-membered cycloadducts with loss of hydrogen cyanide.
- Hoffmann, H. M. R.,Giesel, Kunibert,Lies, Reinhard,Ismail, Zeinhom M.
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p. 548 - 551
(2007/10/02)
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- SYNTHESIS OF DIASTEREOISOMERIC 2,4,7-TRIOXA-3-PHOSPHA-3-R-3-THIONOBICYCLO(4.4.0) DECANES AS A MODEL FOR PHOSPHORUS NUCLEOPHILIC SUBSTITUTION STUDIES.
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2,4,7-Trioxa-3-chloro, 3-fluoro, 3-dimethylamino, 3-methoxy, 3-(2-propanoxy)-3-phospha-3-thionobicyclo (4.4.0) decanes (trans fusion) have been prepared.The precursor diol, 2-hydroxymethyl-3-hydroxytetrahydropyran (2R*, 3S*), was obtained in two steps from 3,4-dihydro-2H-pyran.The chloridates 7a and 7b were separated by high performance liquid chromatography and the stereochemistry of the nucleophilic substitution at phosphorus (with fluoride anion, dimethylamine, methanol, 2-propanol) for each isomer was studied.The substitution of chlorine was found to occur mostly with inversion of configuration for the two isomers.Equilibrium constants were measured for 7a7b and 9a9b making it possible to calculate the corresponding standard free energies.A kinetic study of the 2-propanolysis of 7a and 7b showed that 7b reacted more slowly than 7a.It was found that the difference between the free energy of activation (ΔΔG (b-a)=1 Kcal/mol for the two isomers is close to the calculated value of the standard free energy variation ΔG0 (b-a)=-1.3 Kcal/mol.The difference between the observed reaction rates is probably due to the relative thermodynamic stabilities of the reactants.
- Bouchu, D.,Dreux, J.
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