Tandem Payne/Meinwald versus Meinwald rearrangements on the α-hydroxy- or α-silyloxy-spiro epoxide skeleton.

Under Lewis acid activation, the new α-hydroxy-spiro epoxide scaffold 1a underwent an original tandem Payne/Meinwald rearrangement affording the cyclopentyl hydroxymethylketone 6 in a stereospecific manner, while a Meinwald-type epoxide rearrangement occurred when the derived α-trimethylsilyloxy-spiro epoxide 2a was treated with MABR, yielding stereoselectively the cyclohexane carbaldehyde 9.

ortho-Lithium/magnesium carboxylate-driven aromatic nucleophilic substitution reactions on unprotected naphthoic acids.

Substitution of an ortho-fluoro or methoxy group in 1- and 2-naphthoic acids furnishing substituted naphthoic acids occurs in good to excellent yields upon reaction with alkyl/vinyl/aryl organolithium and Grignard reagents, in the absence of a metal catalyst without the need to protect the carboxyl (CO(2)H) group. This novel nucleophilic aromatic substitution is presumed to proceed via a precoordination of the organometallic with the substrate, followed by an addition/elimination.

Selectivity in C-alkylation of dianions of protected 6-methyluridine.

A regioselective synthesis of 6-ω-alkenyluridines 3, precursors of potent antiviral and antitumor cyclonucleosides 5, is described. While ω-alkenyl halides do not alkylate 6-lithiouridine, compounds 3 were prepared in a regioselective manner by sequential treatment of 6-methyluridine 2 with LTMP or LDA (4 equiv) in THF at -30 °C followed by alkylation with ω-alkenyl bromides.

Asymmetric synthesis of cyclohexene nucleoside analogues.

The asymmetric synthesis of novel cyclohexene nucleoside analogues 12 and 15 is described. An enantiospecific Diels-Alder reaction between (E,E)-diene 2 and (+)-5-(d-mentyloxy)-2(5H)-furanone 3 provided the cycloadduct isomer 4. Three additional steps yielded amine 8 allowing the constructions of the thymine and adenine moieties to afford intermediates 11 and 14, respectively.

Evidence for a trianion intermediate in the metalation of 4-hydroxy-6,7-dimethoxy-8-methyl-2-naphthoic acid. Methodology and application to racemic 5,5'-didesisopropyl-5,5'-dialkylapogossypol derivatives.

The metalation of 4-hydroxy-6,7-dimethoxy-8-methyl-2-naphthoic acid (8) affording trianion 6 is presented and applied to the regioselective efficient construction of a series of 5,5'-didesisopropyl-5,5'-dialkylapogossypol derivatives 3 that are potent pan-active inhibitors of antiapoptotic Bcl-2 family proteins.

Synthesis of N-aryl and N-alkyl anthranilic acids via S(N)Ar reaction of unprotected 2-fluoro- and 2-methoxybenzoic acids by lithioamides.

Substitution of the fluoro or methoxy group in unprotected 2-fluoro- and 2-methoxybenzoic acids to afford N-aryl and N-alkyl anthranilic acids occurs upon reaction with lithioamides under mild conditions in the absence of a metal catalyst.

Solid-phase de novo synthesis of a (+/-)-2-deoxy-glycoside.

The solid-phase synthesis of methyl 2-deoxy-3-O-benzyl-D,L-arabino-hexopyranoside was achieved in a six-step sequence via a de novo strategy based on the hetero-Diels-Alder reaction of a vinyl ether supported on an azalactone-functionalized polystyrene resin, followed by the functional modification of the heteroadduct and the final release of the methyl glycoside by acidic solvolysis.

Synthesis and glycosidase inhibitory activity of 1-amino-3,6-anhydro-1-deoxy-D-sorbitol derivatives.

3,6-Anhydro-1-(aryl or alkylamino)-1-deoxy-D-sorbitol derivatives have been prepared in four steps from isosorbide, a by-product from the starch industry. The inhibitory activities of these new compounds have been evaluated towards 13 glycosidases. A first lead-compound was identified, which inhibited beta-N-acetylglucosaminidase from bovine kidney (82% inhibition at 1mM).

On the mechanism of the directed ortho and remote metalation reactions of N,N-dialkylbiphenyl 2-carboxamides.

A study concerning the mechanism of the LDA-mediated ortho and remote metalation of N,N-dialkyl-2-biphenyl carboxamides (e.g., 4a) is reported.

Solvent-free direct reductive amination by catalytic use of an organotin reagent incorporated on an ionic liquid.

An organotin reagent supported on an ionic liquid was used as a highly effective catalyst (down to 0.1 mol%) for the direct reductive amination of aldehydes and ketones using PhSiH3; this solvent-free method facilitates purification of the products, thus minimizing the contamination by tin.

Electrochemistry and reactivity of surface-confined catechol groups derived from diazonium reduction. Bias-assisted Michael addition at the solid/liquid interface.

We have designed a novel catechol-modified electrode that could be used for bias-assisted Michael addition at the solid/liquid interface. The glassy carbon electrode was modified by the electrochemical reduction of a catechol para-substituted phenyldiazonium salt. The electrochemistry of surface-confined catechol moieties was investigated by cyclic voltammetry.

Cyclopropenylcarbinol derivatives as new versatile intermediates in organic synthesis: application to the formation of enantiomerically pure alkylidenecyclopropane derivatives.

The copper-catalyzed carbomagnesiation (or hydrometalation) reaction of chiral cyclopropenylcarbinol derivatives, obtained by means of a kinetic resolution of secondary allylic alcohols, leads to an easy and straightforward preparation of enantiomerically pure alkylidenecyclopropane derivatives. The reaction mechanism is composed of a syn-carbometalation followed by a syn-elimination reaction. To gain further insight into the reaction mechanism of the carbometalation, the diastereoselective formation of cyclopropylcarbinol was also achieved and was found to be very sensitive to the nature of the organometallic species used for the addition reaction.

Hetero-Diels-Alder reactions of cyclic ketone derived enamide. A new and efficient concept for the asymmetric Robinson annulation.

Chiral enamides, easily prepared in one step from a cyclic ketone and an oxazolidinone, are successfully employed in high-yielding, endo, and facially selective Hetero-Diels-Alder reactions involving activated oxadienes and Siever's reagent as catalyst. From the resulting bicyclic heteroadducts, a novel and efficient asymmetric modification for the Robinson annulation of cyclic monoketones is described.

In situ formation of diazonium salts from nitro precursors for scanning electrochemical microscopy patterning of surfaces.

Give me a tip: In situ production of diazonium salts from nitro compounds allows the use of diazonium chemistry for microelectrochemical patterning of surfaces by scanning electrochemical microscopy. The nitro precursor is reduced at the tip to the amine, which is diazotized in the interelectrode space as it diffuses (see picture). The tip acts as a source of diazonium salts, allowing sample derivatization just beneath the tip.

Deprotection of arenediazonium tetrafluoroborate ethers with BBr3.

Ether cleavage was carried out on arene bearing a diazonium salt. The deprotection takes place with boron tribromide under very mild conditions in good yields without affecting the diazonium group.

Development of a phase-controlled constant-distance scanning electrochemical microscope.

The present shear-force constant-distance scanning electrochemical microscope regulates tip-to-substrate distance using a phase-controlled feedback mechanism that is more sensitive than the amplitude-controlled constant-distance scanning electrochemical microscopes. Phase control responds faster to frequency perturbation and presents enhance sensitivity during distance curves under constant-distance mode.

High-pressure hetero-Diels-Alder route to (+/-)-6,6,6-trifluoro-beta-C-naphthyl glycosides.

The first de novo synthesis of a beta-C-naphthyl glycoside displaying a convenient functionality for subsequent transformations into complex C-aryl glycosides is reported. The synthesis of this (+/-)-beta-C-1,5-dibenzyloxynaphthyl 6,6,6-trifluoro-3-amino glycoside relies on a hyperbaric HDA reaction involving a new 2-vinylnaphthalenic dienophile.

N-benzyl aspartate nitrones: unprecedented single-step synthesis and [3 + 2] cycloaddition reactions with alkenes.

N-benzyl aspartate nitrones 2, prepared by addition of N-benzylhydroxylamine to dialkyl acetylenedicarboxylates 1, underwent [3 + 2] thermal cycloaddition with a wide range of alkenes to afford isoxazolidines 4 bearing a polyfunctionalized quaternary center. Under these uncatalyzed conditions, the trans stereocontrol observed with vinyl ethers is higher than that obtained with all acyclic activated nitrones reported to date. The first asymmetric access to a type-4 pure adduct was achieved starting from the chiral aspartate nitrone derived from (S)-alpha-methylbenzylhydroxylamine.

Synthesis of a C-glucosylated cyclopropylamide and evaluation as a glycogen phosphorylase inhibitor.

The synthesis of carbohydrate-based glycogen phosphorylase inhibitors is attractive for potential applications in the treatment of type 2 diabetes. A titanium-mediated synthesis led to a benzoylated C-glucosylated cyclopropylamine intermediate, which underwent a benzoyl migration to afford the corresponding 2-hydroxy-C-glycoside. X-ray crystallographic studies revealed a unit cell composed of four molecules as pairs of dimers connected through two hydrogen bonds.

Redox and ion-exchange properties in surface-tethered DNA-conducting polymers.

A poly(cyclopentadithiophene) matrix modified by DNA covalently fixed to the surface has been designed to study the redox and ion-exchange properties in surface-tethered DNA-conducting polymers. Voltammetric investigations show an improvement in conductivity, originating from DNA modification, probably due to changes in charged-density and size of dopant species. Cyclic voltammetry with concomitant QCM measurements indicate that the mass changes are consistent with an ejection of Na(+) cations associated to the anionic phosphate groups, attesting a DNA contribution to the p-doping process.

Use of telechelic cis-1,4-polyisoprene cationomers in the synthesis of antibacterial ionic polyurethanes and copolyurethanes bearing ammonium groups.

New crosslinked ionic polyurethanes and copolyurethanes were yielded by reaction of telechelic cis-1,4-oligoisoprenes, bearing a variable number of ammonium and hydroxy groups, with isocyanurate of isophorone diisocyanate (I-IPDI). Aiming for a comparative study, polyurethane elastomers based on non-ionic telechelic oligomers were also synthesized. Thermo-mechanical behavior and crosslinking density of these three families of materials were investigated by DMTA and swelling test, respectively.

First general, direct, and regioselective synthesis of substituted methoxybenzoic acids by ortho metalation.

New general methodology of value in aromatic chemistry based on ortho-metalation sites in o-, m-, and p-anisic acids (1-3) (Scheme 1) is described. The metalation can be selectively directed to either of the ortho positions by varying the base, metalation temperature, and exposure times. Metalation of o-anisic acid (1) with s-BuLi/TMEDA in THF at -78 degrees C occurs exclusively in the position adjacente to the carboxylate.

Lewis acid tuned facial stereodivergent HDA reactions using beta-substituted N-vinyloxazolidinones.

The [4 + 2] acido-catalyzed heterocycloaddition between new beta-substituted N-vinyl-1,3-oxazolidin-2-ones (with R' = Me, Ar, CH2 Ar) and beta,gamma-unsaturated alpha-ketoesters (R = Ar) afforded heteroadducts with high levels of endo and facial selectivities. A complete reversal of facial differentiation was achieved by varying the Lewis acid, leading to the stereoselective formation of either endo-alpha or endo-beta adducts. [reaction: see text].