A versatile salt-metathesis route to heteroatomic clusters derived from phosphorus and arsenic Zintl anions

Salt metathesis reactions between ethylenediamine (en) solutions of the K(3)E(7) (E = P, As) Zintl phases and post-transition metal halides (InCl(3), TlCl, SnI(2) and PbI(2)) have yielded a family of novel heteroatomic cluster anions, [In(E(7))(2)](3-), [TlE(7)](2-) and [E'E(15)](3-) (E' = Sn, Pb; E = P, As). Several of these new species have been characterized by single-crystal X-ray diffraction as salts of sequestered potassium cations in [K(2,2,2-crypt)](3)[In(P(7))(2)]·3.5py (1), [K(2,2,2-crypt)](2)[TlP(7)]·py (3), [K(18-crown-6)](2)[TlAs(7)] (4b), [K(2,2,2-crypt)](3)[E'P(15)]·en (E' = Sn (5), Pb (6)) and [K(2,2,2-crypt)](3)[SnAs(15)]·2en (7). The presence of all of the cluster anions in solution was confirmed by electrospray mass-spectrometry and by (1)H and (31)P{(1)H} NMR spectroscopy when pertinent.     

Facile synthesis of 1,3-diacetyl-2-methylcyclopentene a versatile synthetic intermediate.

Convenient access to 1,3-diacetyl-2-methylcyclopentene $\text{2}$ is reported by three routes: acetylation of methylcyclopentene ( or cyclohexane), condensation of acetylacetone with 1,2-dibromoethane, and the isomerisation of O-acrtylated dienolate of 1-actyl-2-methylcyclopentene. The process of isomerisation provides best results and its mechanism is discussed.     

A versatile and highly stereoselective access to vinyl triflates derived from 1,3-dicarbonyl and related compounds

1,3-Dicarbonyl derivatives, such as 1,3-diketones, beta-ketoaldehydes, beta-ketoesters, beta-ketoamides, beta-ketophosphonates and beta-ketosulfones were efficiently converted to the corresponding Z vinyl triflates with high stereoselectivity. Precoordination with lithium triflate in dichloromethane and enolization with mild bases such as trialkylamines or DBU followed by trapping with triflic anhydride probably accounted for such high selectivity, achieved even at 0 degrees C. This method offers the first direct route to vinyl triflates from beta-ketoamides, beta-ketophosphonates and beta-ketosulfones.     

Phenacyl bromide: A versatile organic intermediate for the synthesis of heterocyclic compounds

Phenacyl bromides are used as a building blocks in synthetic organic chemistry, which serves as a key model for the development of various biologically important heterocyclic compounds and other industrially important scaffolds. This review covers recent synthetic advances in the preparation of heterocyclic compounds utilizing various phenacyl bromides. A wide range of five- and six-membered heterocyclic compounds as well as fused heterocyclic compounds were synthesized efficiently from the phenacyl bromide precursors through one-pot multicomponent reactions.     

Isolable analogues of the Breslow intermediate derived from chiral triazolylidene carbenes

Since Breslow's initial report on the thiamine mode of action, the study of catalytic acyl carbanion processes has been an area of immense interest. With the advent of azolylidene catalysis, a plethora of reactivtiy has been harnessed, but the crucial nucleophilic intermediate proposed by Breslow had never been isolated or fully characterized. Herein, we report the isolation and full characterization of nitrogen analogues of the Breslow intermediate. Both stable and catalytically relevant, these species provide a model system for the study of acyl carbanion and homoenolate processes catalyzed by triazolylidene carbenes.     

A cyclic enamine derived from 1,2-O-isopropylidene-alpha-D-xylofuranose as a novel carbohydrate intermediate to achieve skeletal diversity

The commercially available carbohydrate 1,2-O-isopropylidene-alpha-D-xylofuranose was efficiently transformed into the high-added-value synthetic scaffold 8. The transformation requires the synthesis of the 5-O-tosyl derivative 7 and its subsequent intramolecular cyclization under basic conditions to give the cyclic enamine 8. Reaction of 8 with O-, N-, S-, and C-nucleophiles and amino acids allowed its efficient transformation (one-step, high yields, and easy purifications) into fused cyclic sugar derivatives with rather unusual molecular skeletons in a completely regio- and stereoselective manner. The characteristics of the sugar derivative 8 established here, high reactivity, synthetic accessibility, and the potential for conversion into a vast collection of products by the action of different nucleophiles, indicate that it will prove to be a useful chiral intermediate for achieving skeletal diversity. The constrained structures and dense functionalization of the polycyclic sugar derivatives generated from 8 make these compounds promising candidates for use as starting agents for the production of new analogues and as drugs.     

Benzyne click chemistry: synthesis of benzotriazoles from benzynes and azides

A variety of substituted benzotriazoles have been prepared by the [3 + 2] cycloaddition of azides to benzynes. The reaction scope is quite general, affording a rapid and easy entry to substituted, functionalized benzotriazoles under mild conditions.     

Short and versatile route to a key intermediate for lactacystin synthesis

[reaction: see text] A key intermediate 14 for the synthesis of lactacystin 1 has been constructed in four steps and 33% overall yield. The key steps involve cyclization of a suitably functionalized glutamic acid derivative and concomitant alkylation of the resulting beta,beta-diketoester system, C-acylation of the cyclic alpha-amidoketone 9, and decarboxylbenzylation of 12. Alkylation of a related beta,beta-diketoester 5 was additionally achieved with several electrophiles.     

A versatile synthesis of carbapenems from substituted dihydropyrans

Dihydropyrans (1) are converted by hydrolysis and reduction to δ-lactones (3), and then to azetidinones (5) which are key intermediates for the synthesis of carbapenems.     

β-Stannylpropionaldehyde. A versatile cyclopropane building-block

Various functional group-substituted cyclopropanes were prepared in good yield starting from β-tributylstannylproprionaldehyde via homoallylstannanes or γ-hydroxypropylstannanes.     

A simple and efficient synthesis of functionalized cyclic carbonate monomers using a versatile pentafluorophenyl ester intermediate

An improved two-step synthetic route to functionalized cyclic carbonate monomers that features a novel cyclic carbonate intermediate with an active pentafluorophenyl ester group (MTC-OPhF(5)) has been developed. The versatile pentafluorophenyl ester intermediate can be synthesized on the gram to kilogram scale in one high-yielding step and is easy to store and handle on the benchtop. The active pentafluorophenyl ester of MTC-OPhF(5) is amenable to further substitution with suitable nucleophiles such as alcohols and amines to generate functionalized cyclic carbonates in high yields. The substitution reaction is tolerant of a wide variety of functionalities, including various hydrophobic and hydrophilic groups, reactive functionalities (via thiol-ene click chemistry or alkyl halides), and protected acids, alcohols, thiols, and amines. In view of the ever-increasing need for biodegradable and biocompatible polymers, this new methodology provides a simple and versatile platform for the synthesis of new and innovative materials.     

A potent, versatile disulfide-reducing agent from aspartic acid

Dithiothreitol (DTT) is the standard reagent for reducing disulfide bonds between and within biological molecules. At neutral pH, however, >99% of DTT thiol groups are protonated and thus unreactive. Herein, we report on (2S)-2-amino-1,4-dimercaptobutane (dithiobutylamine or DTBA), a dithiol that can be synthesized from l-aspartic acid in a few high-yielding steps that are amenable to a large-scale process. DTBA has thiol pK(a) values that are ~1 unit lower than those of DTT and forms a disulfide with a similar E°' value. DTBA reduces disulfide bonds in both small molecules and proteins faster than does DTT. The amino group of DTBA enables its isolation by cation-exchange and facilitates its conjugation. These attributes indicate that DTBA is a superior reagent for reducing disulfide bonds in aqueous solution.     

Bis(cyclopentadienylthallium)methane: A versatile intermediate for the synthesis of dinuclear cyclopentadienylmetal carbonyl complexes

Bis(cyclopentadienylthallium)methane has been prepared from dicyclopentadienyl-methane and was shown to be a versatile starting material for the synthesis of a series of new dinuclear carbonylmetal complexes. Reactions of CH₂(Cp-Tl)₂ with carbonylhalometal complexes yielded CH₂[CpMn(CO)₃]₂, CH₂[CpFe(CO)Br]₂, CH₂[CpRu(CO)₂Cl]₂, CH₂[CpRu(CO)₂]₂, CH₂[CpRh(CO)₂]₂, CH₂[CpRh(CO)]₂-μ-CO, and CH₂[CpIr(CO)₂]₂. Reduction of the iron and ruthenium halide derivatives was found to give the metalmetal bonded complexes, or the corresponding dianions depending on the time of reaction and the stoichiometry. The reaction of these dianions with methyl iodide to give the methyl derivatives is described. The facile decarbonylation of CH₂[CpRh(CO)₂]₂ and carbonylation of CH₂[CpRh(CO)]₂-μ-CO appears to be a consequence of the proximity of the two metal atoms. In contrast, CH₂[CpIr(CO)₂]₂ does not appear to form an analogous bridging compound under the reaction conditions. Complete spectral and physical data for the compounds are presented.     

Asymmetric syntheses of (-)-lentiginosine and an original pyrrolizidinic analogue thereof from a versatile epoxyamine intermediate

Ready access to natural (-)-lentiginosine and its pyrrolizidinic analogue from a chiral vinylic epoxyamine in a straightforward five-step sequence is presented. Careful use of the RCM reaction on aminotriols and constitutes the key feature of the synthetic pathway. The alpha-amyloglucosidase inhibitory activities of the target compounds were evaluated and showed that the more easily accessible pyrrolizidinic analogue possesses an inhibitory activity quite similar to that of (-)-lentiginosine.     

Reformatsky intermediate. A C-metallated species.

¹³C-NMR and ¹H-NMR spectra of the Reformatsky reagent from t-butylbr$\text{o}$ moacetate, evidence a C-metallated species: within the limits of detectability of the methods, no O-metallated species can be detected in solution.     

Applications of a versatile sol-gel derived renewable electrode for capillary electrophoresis

A new electrode has been developed and applied for amperometric detection in capillary electrophoresis (CE), comprised of carbon sol-gel composite material. The versatility of the sol-gel technique permits the flexible configuration of the electrode. The performance of such a sol-gel carbon composite electrode (CCE) is first evaluated in a typical CE application for the detection of purine-based compounds. Application of the CCE is also demonstrated for the detection of phenolic compounds in a micellar system. Separation resolution for non-ionic phenolic compounds can significantly be enhanced by introducing sodium dodecyl sulfate (SDS) at a concentration above its critical micelle concentration (cmc) to the buffer. Another design of the CCE incorporating the electrocatalyst Cu2O is employed for the analysis of sugars and organic acids based on dynamic modification with cetyltrimethylammonium bromide (CTAB). It has been found that the presence of surfactant in the separation buffer does not adversely influence the electrochemical detection using a sol-gel derived carbon electrode.