Synthesis of nitrogen-containing spirocyclic scaffolds via aminoallylation/RCM sequence

A concise route to nitrogen-containing spirocyclic scaffolds was developed. It is based on the allylation of imines derived from cyclic ketones. The resulting homoallylamines were subsequently alkylated with bromomethylmethacrylate resulting in propenyl-butenyl substituted amine derivatives. Basic amines such as 4 or 10 were cyclized with the Grubbs 2nd generation catalyst in the presence of pTsOH. Carbamate derivatives could be converted to tetrahydropiperidine derivatives with the same catalyst. It could be shown that the acrylate functionality can be degraded to the ketone using the classical sequence consisting of Curtius rearrangement of the derived acrylic acid followed by hydrolysis of the vinyl isocyanate. Other modifications include reduction of the acrylate double bond, saponification of the ester group, and amide formation.     

Diversity-oriented approach to biologically relevant molecular frameworks starting with beta-naphthol and using the Claisen rearrangement and olefin metathesis as key steps

A diversity-oriented approach for the synthesis of various structurally different molecular frameworks from readily accessible and common precursors is described. A Claisen rearrangement followed by ring-closing metathesis or ethylene-promoted ring-closing enyne metathesis has been utilized as the key synthetic transformation to generate naphthoxepine derivatives. The ring-closing metathesis approach has also been used to generate spirocyclic compounds and the pleiadene framework.     

A core-shell nanoparticle approach to photoreversible fluorescence modulation of a hydrophobic dye in aqueous media

Amphiphilic core-shell nanoparticles containing spiropyran moieties have been prepared in aqueous media. The nanoparticles consist of hydrophilic and biocompatible poly(ethyleneimine) (PEI) chain segments, which serve as the shell, and a hydrophobic copolymer of methyl methacrylate (MMA), a spiropyran-linked methacrylate, and a cross-linker, which forms the core of the nanoparticles. A hydrophobic fluorescent dye based on the nitrobenzoxadiazolyl (NBD) group was introduced into the nanoparticles to form NBD-nanoparticle complexes in water. The nanoparticles not only greatly enhance the fluorescence emission of the hydrophobic dye NBD in aqueous media, probably by accommodating the dye molecules in the interface between the hydrophilic shells and the hydrophobic cores, but also modulate the fluorescence of the dye through intraparticle energy transfer. This biocompatible and photoresponsive nanoparticle complex may find applications in biological areas such as biological diagnosis, imaging, and detection. In addition, this nanoparticle approach will open up possibilities for the fluorescence modulation of other hydrophobic fluorophores in aqueous media.     

Synthesis, structure and emission properties of spirocyclic benzofuranones and dihydroindolones: a domino insertion-coupling-isomerization- Diels-Alder approach to rigid fluorophores

An alkynoyl ortho-iodo phenolester or alkynoyl ortho-iodo anilides and propargyl allyl ethers react under Sonogashira coupling conditions in the sense of an insertion-coupling-isomerization-Diels-Alder hetero domino reaction to furnish (tetrahydroisobenzofuran)-spirobenzofuranones and -spirodihydroindolones in good yields. Many representatives can be crystallized and single crystal structure analyses display steric and electronic substituent effects on the torsional angles of the terminal (hetero)aryl groups and the central cis,trans-butadiene fragment. DFT computations reveal that in the final pericyclic step the Diels-Alder termination is by far thermodynamically and kinetically favored over a possible Claisen rearrangement. Compounds of this new class of spirocyclic compounds possess large Stokes shifts and fluoresce intensively with blue over green to orange colors. As a consequence of the spirocyclic rigidity fluorescence lifetimes and quantum yields are rather high in some cases.     

Studies towards the total synthesis of (−)-borrelidin: a strategy for the construction of the C11-C15 cyanodiene fragment and the utility of RCM for macrocyclization using model systems

We report here a methodology for the construction of a conjugated cyanodiene synthon and the propensity of such synthons to participate in the olefin metathesis reaction. To this end, we have developed a strategy for the construction of the C11-C15 fragment of borrelidin and demonstrated the utility of the RCM reaction in the preparation of the final macrolide. To our knowledge, this is the first example of a RCM with a nitrile functionality on a diene.     

New strategies to symmetric and unsymmetric cyclic sulfamide analogs of DMP 323: a ‘sulfur linchpin’/RCM approach

The synthesis of 7-membered cyclic sulfamides utilizing the RCM reaction is described herein. Two major synthetic strategies that expand the scope and utility of our previously reported sulfamide and sulfamoyl carbamate chemistry are employed. Both Mitsunobu alkylation and simple alkylation of core sulfamides and sulfamoyl carbamates coupled with RCM are used to efficiently install lipophilic groups into the P1/P1′ and P2/P2′ periphery of the cyclic sulfamides. Overall, the routes described are applicable to the synthesis of a variety of cyclic 7-membered sulfamides.     

A carbohydrate based approach towards the synthesis of aspercyclide C

A formal total synthesis of aspercyclide C (3) is described in which d-ribose is employed as a chiral pool material. The key step is a ring closing metathesis.     

A practical and green approach towards synthesis of new N-sulfonylimines under ultrasound irradiation

An efficient protocol was developed for the synthesis of N-sulfonylimines under environment friendly conditions. Ultrasonic energy was employed to obtain the desired products in excellent yields with high purity under solvent- and catalyst-free conditions. The synthesis of new N-sulfonylimines was accomplished from various N-sulfonamides and benzaldehyde.

The structures of the synthesized compounds are confirmed by elemental analysis as well as by ¹H, ¹³C NMR spectral data, IR and MS.     

A Formal Total Synthesis of Eleutherobin Using the Ring‐Closing Metathesis (RCM) Reaction of a Densely Functionalized Diene as the Key Step: Investigation of the Unusual Kinetically Controlled RCM Stereochemistry

Asymmetric oxyallylation reactions and ring‐closing metathesis have been used to synthesize compound 3 , a key advanced intermediate used in the total synthesis of eleutherobin reported by Danishefsky and co‐workers. The aldehyde 6 , which is readily prepared from commercially available R‐(?)‐carvone in six steps in 30 % overall yield on multigram quantities, was converted into the diene 5 utilizing two stereoselective titanium‐mediated Hafner–Duthaler oxyallylation reactions. The reactions gave the desired products ( 8 and 12 ) in high yields (73 and 83 %, respectively) as single diastereoisomers, with the allylic alcohol already protected as the p‐methoxyphenyl (PMP) ether, which previous work has demonstrated actually aids ring‐closing metathesis compared to other protective groups and the corresponding free alcohol. Cyclization under forcing conditions, using Grubbs' second‐generation catalyst 13 , gave the ten‐membered carbocycle (E)‐ 14 in 64 % yield. This result is in sharp contrast to similar, but less functionalized, dienes, which have all undergone cyclization to give the Z stereoisomers exclusively. A detailed investigation of this unusual cyclization stereochemistry by computational methods has shown that the E isomer of the ten‐membered carbocycle is indeed less thermodynamically stable than the corresponding Z isomer. In fact, the selectivity is believed to be due to the dense functionality around the ruthenacyclobutane intermediate that favors the trans‐ruthenacycle, which ultimately leads to the less stable E isomer of the ten‐membered carbocycle under kinetic control. During the final synthetic manipulations the double bond of enedione (E)‐ 16 isomerized to the more thermodynamically stable enedione (Z)‐ 4 , giving access to the advanced key‐intermediate 3 , which was spectroscopically and analytically identical to the data reported by Danishefsky and co‐workers, and thereby completing the formal synthesis of eleutherobin.     

A simple and efficient approach to the synthesis of highly functionalized fused benzochromenes

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate or dibenzoylacetylene, by 1-naphthol, 2-naphthol, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene or 4-methyl-8-hydroxycoumarin leads to vinylnitrilium cations, which undergo carbon-centered Michael type addition with the conjugate base of the naphthols to produce highly functionalized benzochromenes.     

Incorporation of spiroxanthene units in blue-emitting oligophenylene frameworks: a new molecular design for OLED applications

We report herein the incorporation of xanthenyl units into two extended π-conjugated phenylene systems, namely indenofluorene and pentaphenylene. Thus, dispiroxanthene-indenofluorene (DSX-IF) and dispiroxanthene-ladderpentaphenylene (DSX-LPP) have been designed and synthesized through short and efficient synthetic approaches. These two molecules possess a 3π-2-spiro architecture (3π-systems/2-spiro bridges), in which two xanthenyl cores are spirolinked to a π-conjugated backbone either indenofluorene for DSX-IF or pentaphenylene for DSX-LPP. The structural, electrochemical, and photophysical properties of these blue/violet emitters have been studied in detail and compared to those of their 'all carbon' analogues with spirofluorenyl cores instead of spiroxanthenyl cores, namely dispirofluorene-indenofluorene (DSF-IF) and dispirofluorene-ladderpentaphenylene (DSF-LPP), previously reported in the literature. Finally, the application of DSX-IF and DSX-LPP as new light-emitting materials in nondoped organic light emitting diodes is reported. A detailed optical study of the different electroluminescence spectra is notably presented, with an emphasis 1) on the origin of the low-energy emission band observed in the case of DSX-LPP and 2) on the unexpected optical contribution of the well-known hole-transporting-layer NPB (N,N'-di(naphtyl)-N,N'-diphenyl(1,1'-biphenyl)-4,4'-diamine).     

Study on the electric double layer of a cylindrical reverse micelle with functional theoretical approach

Some surfactants, such as AOT (bis-(2-ethylhexyl sodium sulfosuccinate), have such a special structure with a smaller hydrophilic head group but a bigger hydrophobic tail. Some mixtures of surfactants (or surfactant/co-surfactant) also take the same special structure[1―3]. If their concentrations are much higher than their critical micelle concentrations (cmc) in oil/water system, these surfactants or mixtures usually assemble as W/O cylindrical (or wormlike) micelles with their lengths bei…     

Total syntheses of zaragozic acids A and C by a carbonyl ylide cycloaddition strategy

A carbonyl ylide cycloaddition approach to the squalene synthase inhibitors zaragozic acids A and C is described. The carbonyl ylide precursor 8 was synthesized starting from di-tert-butyl D-tartrate (47) via an eleven-step sequence involving the regioselective reduction of the mono-MPM (MPM=4-methoxybenzyl) ether 48 with LiBH4 and the diastereoselective addition of sodium tert-butyl diazoacetate to alpha-keto ester 10. The reaction of alpha-diazo ester 8 with 3-butyn-2-one (40) in the presence of a catalytic amount of [Rh2(OAc)4] gave the desired cycloadduct 59 as a single diastereomer. The dihydroxylation of enone 59 followed by sequential transformations permitted the construction of the fully functionalized 2,8-dioxabicyclo[3.2.1]octane core 5. Alkene 79 derived from 5 serves as a common precursor to zaragozic acids A (1) and C (2), since the elongation of the C1 alkyl side chain can be attained by olefin cross-metathesis, especially under the influence of Blechert's catalyst (85).     

A practical and green approach towards synthesis of multisubstituted imidazoles using boric acid as efficient catalyst

An efficient one-pot, cyclocondensation of ammonium acetate, 1,2-diphenyl ethanedione, aromatic aldehyde or arylamine, and catalyzed by boric acid is achieved to form multisubstituted imidazole derivatives. Boric acid as green property is harmless to the environment and has improved the yield of multisubstituted imidazole derivatives. Moreover, we have tested the biological activities of imidazole derivatives by the four fungi. And the investigations showed most of imidazole derivatives have antifungal action on four fungus.