- 2-Pyrones possessing antimicrobial and cytotoxic activities
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The 2-pyrone sub-unit is found in a number of natural products possessing broad spectrum biological activity. Such compounds are validated as being capable of binding to specific protein domains and able to exert a remarkable range of biological effects. In an effort to identify synthetic 2-pyrones with interesting biological effects, herein we report the synthesis and biological evaluation of 4-substituted-6-methyl-2-pyrones. Synthetic routes to 4-alkyl/alkenyl/aryl/alkynyl-6-methyl-2-pyrones have been developed utilising Sonogashira, Suzuki and Negishi cross-coupling starting from readily available 4-bromo-6-methyl-2-pyrone. Specific conditions for each organometallic protocol were required for successful cross-coupling. In particular, a triethylamine/acetonitrile - base/solvent mixture was crucial to Sonogashira alkynylation of 4-bromo-6-methyl-2-pyrone, whereas thallium carbonate was a mandatory base for the Suzuki cross-coupling of trialkylboranes. The 2-pyrones demonstrate potent inhibitory activity against Bacillus subtilis, Escherichia coli, Staphylococcus aureus, Schizosaccharomyces pombe and Botrytis cinerea. The growth inhibitory activities of selected 2-pyrones were determined in A2780 human ovarian carcinoma and K562 human chronic myelogenous leukaemia cell lines using an in vitro cell culture system (MTT assay). These studies demonstrate that 4-phenylethynyl-, 4-tetrahydropyranylpropargyl ether- and 4-ethynyl-6-methyl-2-pyrones have excellent potential as a new class of anticancer agents.
- Fairlamb, Ian J. S.,Marrison, Lester R.,Dickinson, Julia M.,Lu, Feng-Ju,Schmidt, Jan Peter
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- Rate dependence on inductive and resonance effects for the organocatalyzed enantioselective conjugate addition of alkenyl and alkynyl boronic acids to β-indolyl enones and β-pyrrolyl enones
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Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.
- Boylan, Amy,Li, Jian-Yuan,Lundy, Brian J.,May, Jeremy A.,Nguyen, Thien S.,Sundstrom, Sasha,Vallakati, Ravikrishna
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- A Tunable Route to Prepare α,β-Unsaturated Esters and α,β-Unsaturated-γ-Keto Esters through Copper-Catalyzed Coupling of Alkenyl Boronic Acids with Phosphorus Ylides
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A tunable strategy to prepare α,β-unsaturated esters and α,β-unsaturated-γ-keto esters in good to excellent yields was developed through copper-catalyzed oxidative coupling of phosphorus ylides with alkenyl boronic acids under mild conditions. The reaction without water afforded α,β-unsaturated esters, ketones, and amides while α,β-unsaturated-γ-keto esters, 1,4-α,β-unsaturated diketones and α,β-unsaturated-γ-keto amides were obtained when using 5.0 equiv. of water. H2O18 labeling experiments showed that water played an important role in the formation of α,β-unsaturated-γ-keto esters. A plausible formation mechanism for α,β-unsaturated esters and α,β-unsaturated-γ-keto esters was proposed based on mechanistic studies. Phosphonium salts could also be used directly as coupling partners instead of phosphorus ylides. The reaction exhibited a broad substrate scope, good functional group tolerance, good regioselectivity, and diverse coupling products. (Figure presented.).
- Bi, Hong-Yan,Liu, Feng-Ping,Liang, Cui,Su, Gui-Fa,Mo, Dong-Liang
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supporting information
p. 1510 - 1516
(2018/03/05)
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- Rhodium(III)-catalyzed cross-coupling of alkenylboronic acids and N -pivaloyloxylamides
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Rh(III)-catalyzed umpolung amidation of alkenylboronic acids for the synthesis of enamides is reported. This reaction proceeds readily at room temperature and displays an extremely wide spectrum of functional group tolerance. With cooperation of hydrobora
- Feng, Chao,Loh, Teck-Peng
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supporting information
p. 3444 - 3447
(2014/07/21)
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- Lithium bis(ethylenedioxyboryl)methide and its reactions with carbonyl compounds and with the chlorotriphenyl derivatives of germanium, tin and lead
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Transesterification of tris(dimethoxyboryl)methane, HC[B(OCH3)2]3, with ethylene glycol yielded tris(ethylenedioxyboryl)methane (I), HC(BO2C2H4)3 which with methyllithium in THF at -70°C precipitated lithium bis(ethylenedioxyboryl)methide (II), Li+ HC(BO2C2H4)2-. Reaction of II with Ph3MCl, where M = Ge, Sn, or Pb, gave Ph3MCH(BO2C2H4)2. The analogous 1,3-propanediol ester, Li+HC(BO2C3H6)2-, yielded Ph3MCH(BO2C3H6)2. Treatment of Ph3SnCH(BO2C2H4)2 with MeLi followed by Ph3SnCl gave (Ph3Sn)2CHBO2C2H4, showing that one B and one Sn atom are sufficient to stabilize a carbanion. Reaction of II with aldehydes gave high yields of 1-alkene-1-boronic esters, RCHCHBO2C2H4, with unexpectedly high stereoselectivity, 90-100% trans by NMR analysis. Aqueous work-up of these boronic esters yielded the boronic acids, RCHCHB (OH)2, which crystallized as the pure trans isomers. Ketones react with II in an analogous manner. The reaction with acetophenone was not stereospecific. Functional group compatibility has been demonstrated in condensations of II with 1,3-dichloroacetone, cinnamaldehyde, p-nitrobenzaldehyde, and p-dimethylaminobenzaldehyde. The trans geometry of the major isomer of CH3CHCHBO2C2H4 was proved by B-butylation with butyllithium followed by rearrangement with iodine and base to form cis-2-heptene, a sequence of known stereochemistry, and analogous structure proofs were carried out with cis-CH3CHCHBO2C2H4 and trans-C6H5CHCHBO2C2H4.
- Matteson, Donald S.,Jesthi, Pradipta K.
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