Tak-Hang Chan

Organic syntheses using indium-mediated and catalyzed reactions in aqueous media

I. Introduction 11. Indium Mediated Barbier-Type Reactions 2.1. The reaction 2.2. Mechanism of indium-mediated Barbier-type reactions 2.3. The regio- and stereochemistry of indium-mediated reactions 2.4. Synthetic applications of indium-mediated reactions 2.4.1. Synthesis of sialic acids and carbohydrate homologations 2.4.2. Styryl carbohydrates 2.4.3. 13-Lactams 2.4.4. Carbocycles 2.4.5. Other examples III. Transmetalation Reactions with Indium Metal or Indium Salts IV. Other Indium-Mediated Reactions V. Indium Salts as Water-Tolerant Lewis Catalysts 5.1. Barbier-type reactions 5.2. Mukaiyama-aldol reactions 5.3. Other reactions VI. Conclusions 11149 11150 11150 11153 11154 11160 11160 11164 11165 11165 11167 11167 11168 11170 11170 11170 11171 11172 1. Introduction While the development of boron and aluminum reagents for synthetic purposes has been one of the major achievements in organic chemistry in this century, the study of indium reagents has remained largely unexplored until very recently.t The earliest study of using indium for synthetic purposes was carried out briefly earlier this century.2 In the 1970s, Rieke developed various active metals (including indium), now commonly referred to as 0040-4020/99/

BoraneBu2BOTf: A mild reagent for the regioselective reductive ring opening of benzylidene acetals in carbohydrates

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Chemistry of allene oxides

BH3Bu2OTf is an effective reagent to reductively cleave 4,6-O-benzylidene acetals of various hexopyranosides to the corresponding 4-O-benzyl ethers. 4,6-O-Isopropylidene acetals can be similarly cleaved. Common protecting groups are stable to the reaction conditions.

Indium mediated coupling of aldehydes with allyl bromides in aqueous media. the issue of regio- and diastereo-selectivity

Aus Aldehyden (I) erhalt man uber das Carbinol (II) die isomeren Chloride (III) und (IV), die zu den Epoxiden (V) cyclisiert und weiter mit z.B. Fluorid-Ionen zu den Allenoxiden (VI) eliminieren.

Aerobic and Electrochemical Oxidative Cross‐Dehydrogenative‐Coupling (CDC) Reaction in an Imidazolium‐Based Ionic Liquid

Abstract The regio-and diastereo-selectivity in the coupling of γ-substituted allyl bromides with aldehydes mediated by indium in water were found to be dependent on the steric effect of the substitutents on both allyl bromides and the aldehydes.

A Novel Prodrug of Epigallocatechin-3-gallate: Differential Epigenetic hTERT Repression in Human Breast Cancer Cells

The ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF(4)] has demonstrated high efficiency when applied as a solvent in the oxidative nitro-Mannich carbon--carbon bond formation. The copper-catalyzed cross-dehydrogenative coupling (CDC) between N-phenyltetrahydroisoquinoline and nitromethane in [BMIm][BF(4)] occurred with high yield under the described reaction conditions. Both the ionic liquid and copper catalyst were recycled nine times with almost no lost of activity. The electrochemical behavior of the tertiary amine substrate and beta-nitroamine product was investigated employing [BMIm][BF(4)] as electrolyte solvent. The potentiostatic electrolysis in ionic liquid afforded the desired product with a high yield. This result and the cyclic voltammetric investigation provide a better understanding of the reaction mechanism, which involves radical and iminium cation intermediates.

Chemistry of 2,5-bis(trimethylsiloxy) furans. I: Preparation and diels-alder reactions

Epigallocatechin-3-gallate (EGCG), a major component of green tea polyphenols (GTP), has been reported to downregulate telomerase activity in breast cancer cells thereby increasing cellular apoptosis and inhibiting cellular proliferation. However, the major concerns with GTPs are their bioavailability and stability under physiologic conditions. In the present study, we show that treatments with EGCG and a novel prodrug of EGCG (pro-EGCG or pEGCG) dose- and time-dependently inhibited the proliferation of human breast cancer MCF-7 and MDA-MB-231 cells but not normal control MCF10A cells. Furthermore, both EGCG and pro-EGCG inhibited the transcription of hTERT (human telomerase reverse transcriptase), the catalytic subunit of telomerase, through epigenetic mechanisms in estrogen receptor (ER)-positive MCF-7 and ER-negative MDA-MB-231 cells. The downregulation of hTERT expression was found to be because of hTERT promoter hypomethylation and histone deacetylations, mediated at least partially through inhibition of DNA methyltransferase and histone acetyltransferase activities, respectively. In addition, we also observed that EGCG and pEGCG can remodel chromatin structures of the hTERT promoter by decreasing the level of acetyl-H3, acetyl-H3K9, and acetyl-H4 to the hTERT promoter. EGCG and pEGCG induced chromatin alterations that facilitated the binding of many hTERT repressors such as MAD1 and E2F-1 to the hTERT regulatory region. Depletion of E2F-1 and MAD1 by using siRNA reversed the pEGCG downregulated hTERT expression and associated cellular apoptosis differently in ER-positive and ER-negative breast cancer cells. Collectively, our data provide new insights into breast cancer prevention through epigenetic modulation of telomerase by using pro-EGCG, a more stable form of EGCG, as a novel chemopreventive compound. Cancer Prev Res; 4(8); 1243–54. ©2011 AACR.

Facile synthesis of α-hydroxy carbonyl compounds by enolate oxidation with dimethyldioxirane

A number of substituted 2,5-bis (trimethylsioloxy) furans were prepared from the corresponding succinic anhydrides, and were found to be reactive dienes for the Diels-Alder reaction with electron - withdrawing dienophiles, giving p-quinones and hydroquinones.

Indium mediated intramolecular carbocyclization in aqueous media. A facile and stereoselective synthesis of fused α-methylene-γ-butyrolactones

The direct oxidation of enolates with dimethyldioxirane (as a solution in acetone) provides the α-hydroxy derivatives in excellent yield.

Organometallic-type reactions in aqueous media mediated by indium. Allylation of acyloyl-imidazoles and pyrazoles. Regioselective synthesis of β,γ-unsaturated ketones

Abstract Indium mediated intramolecular carbocyclization in aqueous media gave cis-fused α-methylene-γ-butyrolactones selectively in good yields.