- The synthesis of melohenine B and a related natural product
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A concise synthesis of melohenine B and O-ethyl-14-epimelohenine B, from eburnamonine, was achieved via a biomimetic diastereoselective singlet oxygen-mediated oxidative cleavage of the indole C2-C7 bond. These studies enabled the assignment of the absolute configuration of the natural products. In line with a proposed biosynthetic pathway, the resulting nine-membered ring containing products could be converted to the corresponding quinolones.
- Lancefield, Christopher S.,Zhou, Linna,Lébl, Tomas,Slawin, Alexandra M. Z.,Westwood, Nicholas J.
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- Studies in Biomimetic Alkaloid Syntheses. 8. Total Syntheses of the C-14 Epimeric Hydroxyvincadifformines, Tabersonine, a (Hydroxymethyl)-D-norvincadifformine, and the C-20 Epimeric Pandolines
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Condensation of methyl 1,2,3,4,5,6-hexahydroazepinoindole-5-carboxylate (6) with 5-chloro-2-ethyl-4-hydroxypentanal lactol (14) yielded the 14α- and 14β-hydroxyvincadifformines (8a,b) in an epimeric ratio which was solvent dependent.On condensation of the indoloazepine 6 with 4,5-epoxy-2-ethylpentanal (9) the same compounds were formed together wih a (hydroxymethyl)-D-norvincadifformine, 10, as the major product.Dehydration of 14β-hydroxyvincadifformine (8a) readily gave tabersonine (1), while 14α-hydroxyvincadifformine (8b) could only be dehydrated bycarbamate pyrolysis.The latter compound (8b) and the (hydroxymethyl)-D-norvincadifformine 10 could be converted to vincadifformine (18) through the chloromethyl derivative 16.Condensation of the indoloazepine 6 with the epimeric 4,5-dichloro-2-ethylpentanals (19) also gave the (chloromethyl)-D-norvincadifformine 16 and 14β-chlorvinacadifformine (20).Dehydrohalogenation of the latter compound provided a third sequence to tabersonine (1).A synthesis of the C-20 epimeric pandolines (2a,b) from 5-chloro-4-ethyl-4-hydroxypentanal lactol (22) similarly allowed control of the C-20 epimeric product ratio through its solvent dependence.
- Kuehne, Martin E.,Okuniewicz, J. F.,Kirkemo, C. L.,Bohnert, J. C.
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- Synthesis of 5-[(Pentafluorosulfanyl)methyl]-γ-butyrolactones via a Silver-Promoted Intramolecular Cyclization Reaction
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The synthesis of 5-[(pentafluorosulfanyl)methyl]-γ-butyrolactones bearing different substituents at position 3 or 4 is reported. A silver-promoted intramolecular cyclization of substituted 4-chloro-5-(pentafluorosulfanyl)pentanoic acids allows the preparation of the substituted SF5-containing γ-butyrolactones in up to 96 % yield.
- Roudias, Majdouline,Gilbert, Audrey,Paquin, Jean-Fran?ois
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p. 6655 - 6665
(2019/11/03)
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- Copper(II)-Catalyzed Alkene Aminosulfonylation with Sodium Sulfinates for the Synthesis of Sulfonylated Pyrrolidones
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A copper-catalyzed direct aminosulfonylation of unactivated alkenes with sodium sulfinates for the efficient synthesis of sulfonylated pyrrolidones is described. This reaction features good functional group tolerance and wide substrate scope, providing an efficient and straightforward protocol to access this kind of pyrrolidones. Moreover, preliminary mechanistic investigations disclosed that a free-radical pathway might be invovled in the process.
- Rao, Wei-Hao,Jiang, Li-Li,Liu, Xiao-Meng,Chen, Mei-Jun,Chen, Fang-Yuan,Jiang, Xin,Zhao, Jin-Xiao,Zou, Guo-Dong,Zhou, Yu-Qiang,Tang, Lin
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supporting information
p. 2890 - 2893
(2019/04/30)
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- Palladium-Catalyzed Regiocontrollable Reductive Heck Reaction of Unactivated Aliphatic Alkenes
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A general Pd-catalyzed intermolecular reductive Heck reaction of both terminal and internal unactivated aliphatic alkenes has been first developed. This method affords γ- and δ-arylated alkyl carboxylic acid derivatives in high yields with complete anti-Markovnikov selectivity. Notably, the coupling process is stereoretentive for the alkyl chain. Mechanistically, alkyl palladacycle intermediates stabilized by directing group and ligand, hydride species multigenerated from PS/TFA reductant, are two key factors that successfully promote the reaction and regioselectivity.
- Wang, Chengdong,Xiao, Guanlin,Guo, Tao,Ding, Yalan,Wu, Xiaojin,Loh, Teck-Peng
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supporting information
p. 9332 - 9336
(2018/06/29)
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- Kinetics and mechanisms of hydrolysis of tetraphenylporphyrins tethered to silicate glass via a primary or tertiary alcohol linker
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Tetraphenylporphyrins carrying primary or tertiary alcohols in a phenyl group were bonded to silicate glass by heat treatment. The rate of base catalyzed hydrolysis of tertiary ester was 20 times slower than that of primary ester, while the rate of acid catalyzed hydrolysis of tertiary ester was only 2.5 times slower than that of primary ester. Hydrolysis of tertiary alcohol bonded silica in HCl/HO displayed that there is a covalent bond between alcohol oxygen and silicon, and the C-O bond is cleaved under acidic conditions, while the Si-O bond is cleaved under basic conditions.
- Furuta, Nao,Yagi, Takaaki,Mizutani, Tadashi
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supporting information
p. 4336 - 4342
(2014/06/10)
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- Transition-metal catalyzed synthesis of δ-hydroxy-γ-lactones from bis(trimethylsilyl) ketene acetals and allylic acetates via γ-unsaturated carboxylic acids. Comments on the formation of α-cyclopropyl carboxylic acids
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Bis(trimethylsilyl)ketene acetals react with allylic acetates in the presence of Pd(0) complexes to give γ-unsaturated carboxylic acids together with α-cyclopropyl carboxylic acids. The unsaturated acids can be converted catalytically to δ-hydroxy-yγ-lactones by the H2O2/MTO system (methyltrioxorhenium) and to butenolides by Pd(II) catalyzed intramolecular cyclization reactions. The structure of two of these lactones has been established by X-ray analysis. The mechanism of the formation of the cyclopropanic acids will be discussed.
- Rudler, Henri,Harris, Paul,Parlier, Andrée,Cantagrel, Frédéric,Denise, Bernard,Bellassoued, Moncef,Vaissermann, Jacqueline
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p. 186 - 202
(2007/10/03)
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- Syntheses of 20'-Deoxyvinblastine, 20'-Deoxyleurosidine, 20'-Deoxyvincovaline, 20'-epi-20'-Deoxyvincovaline, and 20'-Deoxyvincristine and Its 20'-Epimer through Racemic and Enantioselectively Generated Intermediates. New Syntheses of D/E-cis- and -trans-Ψ
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Vindoline (20), on reaction with chloro imine derivatives of the D-seco-D/E-trans-Ψ- and -20-epi-Ψ-vincadifformines 18 and 19, followed by cyclization and debenzylation steps, provided the natural products 20'-deoxyvinblastine (4) and 20'-deoxyleurosidine
- Kuehne, Martin E.,Bornmann, William G.
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p. 3407 - 3420
(2007/10/02)
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- Effects of α-Substitution on the Rate of Chloromercuriolactonization of Phenyl Esters of γδ-Unsaturated Acids
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Second-order rate constants for the reaction of several phenyl esters of α-alkyl- and/or α-aryl-substituted allyacetic acids with mercury(II) chloride have been determined in 50percent aqueous ethanol.It was found that α-substitution increases the rate of reaction.The rate constants can be correlated with the dual substituent parameter expressions (i) and (ii).In the systems studied the steric coefficient is much larger than the polar one, suggesting that the effect of the substituents on the rate of the reaction is essentially steric in nature, with a small additional contribution from the polar effect. log k2 = log k2o + ρ*?* + δEs (i). log k2 = log k2o + ρ*?* + ψν (ii)
- de Almeida, Maria I.,do Amaral, Antonia T.,do Amaral, Luciano
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p. 1953 - 1958
(2007/10/02)
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- Effects of α Substitution on the Carbonyl Stretching Frequencies of Phenyl Carboxylates
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The infrared carbonyl stretching frequencies for several esters of the general formula R1R2R3C-COOPh were determined in carbon tetrachloride.The ?* and Es Taft parameters as well as the νCharton parameters for the same esters were determined.The carbonyl stretching frequencies are well correlated by a dual substituent parameter treatment: νC=O = νC=O0 + ρ*?* + δES or νC=O = νC=O0 + ρ*?* + ΨνCharton.In both cases the steric parameter is much larger than the polar parameter, suggesting that the effect of the substituents on the carbonyl stretching frequencies is of a steric nature, although a small contribution of the polar effect is observed.
- Almeida, Maria Ines de,Amaral, Antonia T. do,Amaral, Luciano do
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p. 1567 - 1571
(2007/10/02)
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