A novel synthesis of organic diselenapolysulfides

A family of organic polychalcogenides with a common structure of RSeS_xSeR (with x=1, 2, 3 and R=CH₃, Ph, PhCH₂, O₂NC₆H₄CH₂) as well as cyclic 5,5-dimethyl-1,2-dithia-3,7-diselenacycloheptane were synthesized in good yield and high purity from the reaction of Ph₃CS_xCl with corresponding diselenides in chloroform at room temperature. Mechanistic aspects of the insertion involving the formation of an intermediate (RSeS_xCPh₃) are discussed.     

Stereocontrolled synthesis of functionalized 1-azaspirans : Efficient synthesis of perhydrohistrionicotoxin

A formal total synthesis of perhydrohistrionicotoxin (H₁₂-HTX) is described based on a stereocontrolled α-acyliminium ion-olefin cyclisation. In the key step of the synthesis three asymmetric C atoms (C₆ C₇ and C₈) are introduced in a single operation leading to the formation of the spiro formate ester 15. Compound 15 is converted to the spirothiolactam alcohol 17, a known precursor of H₁₂-HTX.The versatility of the synthetic approach is further demonstrated by the stereocontrolled syntheses of other functionalized 1-azaspirans, viz the 6-Endo-Trig products 20 and 24 and the 5-Exo-Trig products 26 and 28. The formation of the latter two compounds is remarkable with respect to the mechanism.¹³C NMR data of a series of 1-azaspirans are provided, which inter alia show the existence of a conformational equilibrium in 1-azaspiro alcohol 16,Mass spectral criteria are used for assignment 5-Exo-or 6-Endo-cyclisation products.     

Asymmetric synthesis of l-proline regio- and stereoselectively labelled with deuterium

A synthesis of l-proline where all of the ring methylenes are stereoselectively labelled with deuterium is described. A catalytic deuteration of protected 3,4-dehydro-l-proline using transition metal catalyst followed by RuO₄-oxidation gave a [3,4-D₂]pyroglutamic acid derivative. A syn-selective deuteration of the aminal derived from the pyroglutamate with Et₃SiD–BF₃·OEt₂ furnished (2S,3S,4R,5S)-[3,4,5-D₃]proline. The present procedure is also applied to the synthesis of the corresponding (2S,3S,4R,5R)-isomer.     

Electrochemical synthesis of network polygermanes and polysilanes

Network σ-conjugated polymers, i.e., a butyl substituted network polygermane, (BuH_xGe)_n (x=0–2), a butyl substituted network polysilane, (BuH_xSi)_n (x=0–2), and an octyl substituted network polysilane, (OctH_xSi)_n (x=0–2), were synthesized by electrochemical reduction of butyltrichlorogermane, butyltrichlorosilane, and octyltrichlorosilane, respectively, for the first time. A polymer of (BuH_xGe)_n (x=0–2) had absorption which extended to 900 nm, while a polymer of (BuH_xSi)_n (x=0–2) and a polymer of (OctH_xSi)_n (x=0–2) had absorption which extended to 500 and 800 nms, respectively. It was found that the reported electrochemical method gave σ-conjugated polymers with more highly developed network structures compared to the other synthetic pathways. The structure of the polymers was successfully controlled from linear to highly developed network structures by controlling the charge for electrosynthesis.     

Superacid-promoted synthesis of indolizidine derivatives

A series of amido-acetals were reacted with the Brønsted superacid, CF₃SO₃H, to provides indolizidine derives by a cyclization cascade. A mechanism is proposed involving formation of a vinylogous enol which undergoes a 6π-electrocyclization reaction with an adjacent N-acyl iminium ion group. With aryl substituents, there is a strong tendency for the N-acyl iminium ion group to undergo Friedel-Crafts type cyclizations with the aryl group. The synthetic methodology was used to prepare the alkaloid natural product, ipalbidine.     

Direct synthesis of mixed methylethyllead alkyls

The reactions of lead oxide, sulphide, and chloride with a mixture of dimethyl- and diethyl-aluminium chloride in the presence of Lewis bases have been studied. Mixtures of methylethyllead compounds of the type Me_4-nPbEt_n (0 ? n ? 4) are formed.A reaction path is proposed.     

Efficient one-pot synthesis of 2-hydroxyethyl per-O-acetyl glycosides

A class of stereo-isomerically-pure alkanediol monoglycosides, 2-hydroxyethyl per-O-acetyl pyranosides (IIIa-IIIf), was conveniently prepared by a one-pot reaction of per-O-acetylated pyranoses (Ia-If) and 2-(tert-butyldimethylsilyloxy)ethanol (II) with catalysis by BF₃·OEt₂. The α-(IIIa) or β-linked glycosides (IIIb-IIIf) with 1,2-trans-configuration were obtained from glycosyl donors with participation of the neighbouring 2-O-acetyl group. BF₃·OEt₂, along with hydrogen fluoride released from BF₃·OEt₂ under the experimental conditions used, facilitates the subsequent de-protection of siloxane to successfully afford 2-hydroxyethyl per-O-acetyl-pyranosides.     

A type 2 Ferrier rearrangement-based synthesis of d-myo-inositol 1,4,5-trisphosphate

The synthesis of d-myo-inositol 1,4,5-trisphosphate (InsP₃) from methyl α-d-glucopyranose, via a type 2 Ferrier rearrangement is reported. A key intermediate in this synthesis possesses orthogonal protecting groups at the 1-, 4- and 5-position, making it a versatile starting point for the synthesis of unnatural InsP₃ derivatives. Biological evaluation of the synthetic InsP₃ demonstrates that this compound evokes selective Ca²⁺ release via activation of InsP₃ receptors.     

Chemo-enzymatic short-step total synthesis of symbioramide

A concise synthesis of symbioramide, a marine-origin ceramide from a common starting material, methyl (±)-trans-2,3-epoxyoctadecanoate, in a convergent manner was achieved. The key step is the direct lipase-catalyzed coupling reaction between methyl (2R,3E)-2-hydroxy-3-octadecenoate and non-protected (±)-erythro-dihydrosphingosine, giving natural (2S,3R,2′R)-symbioramide and its (2R,3S,2′R)-isomer in 38% and 37% yield, respectively. The optically active β,γ-unsaturated α-hydroxyester was prepared by Mg(ClO₄)₂-mediated isomerization of epoxide and the subsequent lipase PS-catalyzed kinetic resolution.     

Novel pseudo-morphotactic synthesis and characterization of tungsten nitride nanoplates

A novel pseudo-morphotactic transformation route was developed to synthesize polycrystalline β-W₂N nanoplates by thermally treating tungstate-based inorganic-organic hybrid nanobelts with a lamellar microstructure in an NH₃ flow. The tungstate-based hybrid nanobelts were formed in a water-in-oil-microemulsion-like “commercial H₂WO₄ powders/n-octylamine/heptane” reaction system. The as-obtained hybrid nanobelts were thermally treated in an NH₃ atmosphere at 650-800 °C for 2 h to form cubic β-W₂N nanoplates. XRD, SEM, TEM, FT-IR and TG-DTA were used to characterize the precursors and their final products. The polycrystalline β-W₂N nanoplates derived from hybrid nanobelts, with side lengths of several hundred nanometers, consist of small nanocrystals with an average grain size of 3.2 nm. The formation of β-W₂N nanoplates involved two steps: decomposing tungstate-based hybrid nanobelts into WO_y and W species and then nitridizing the active W-containing species to β-W₂N nanocrystals in an NH₃ flow. The platelike morphology of the β-W₂N nanocrystals was inherited from the precursor of tungstate-based inorganic-organic hybrid nanobelts.     

The first total synthesis of calabricoside A

Quercetin 3-O-[α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranoside]-7-O-β-d-glucopyranoside (calabricoside A), a new flavonol triglycoside isolated from the aerial parts of Putoria calabrica showing strong radical scavenging activity, was synthesized through a combination of phase-transfer-catalyzed C-3 glycosylation and AgOTf promoted homogeneous C-7 glycosylation in CH₂Cl₂.     

One-pot synthesis of N-allylthioureas using supported reagents

A simple and efficient method has been developed for the synthesis of N-allylthioureas from allylic bromides in one-pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which allyl bromide reacts first with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give the final product, N-allylthiourea, in good yield.     

Stereoselective total synthesis of almorexant

A highly stereoselective synthesis of almorexant has been achieved using (R)-tert-butanesulfinamide as a chiral source. The chiral tetrahydroisoquinoline core was constructed through allylation of chiral N-sulfinyl imine followed by ring closure of the secondary amide with a tethered halide. The chiral α-phenyl amide was introduced by means of S_N2 substitution of (S)-methyl 2-phenyl-2-(tosyloxy)acetate with chiral tetrahydroisoquinoline.     

Total synthesis of amphidinolactone A and its absolute configuration

Asymmetric synthesis of amphidinolactone A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of amphidinolactone A was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural amphidinolactone A.     

Total synthesis of the proposed structure of macrocaffrine

A full account of the total synthesis of 18-demethyl-19-hydroxy-N_a-demethyl-N_b-methylsuaveoline (1), the structure assigned to macrocaffrine isolated from Rauwolfia caffra, is presented. The key steps involved are an intramolecular cycloaddition reaction of the oxazole-olefin 10 and a subsequent dehydration that generated the pentacyclic pyridine derivative 14. The spectral data and specific rotation of synthetic 1 were dissimilar to those reported for a natural sample, leaving the structure of this R. caffra alkaloid undefined.     

A convergent and stereoselective synthesis of a seco-precursor of macrolactin A

A seco-precursor of macrolactin A was synthesized by coupling two advanced segments. Wittig reaction and Horner-Emmons reaction were utilized to construct the three characteristic E,Z and E,E dienes. The C₁-C₁₀ segment was synthesized through Horner-Emmons reaction with phosphonate reagent. The α-alkylation of sulfone stabilized anion with allyl bromide followed by desulfonation gave the C₁₁-C₂₄ segment.     

Regioselective single-step synthesis of 2-aminoimidazole derivatives

A convenient single-step strategy for the regioselective assembly of 2-aminoimidazole derivatives is herein described. Through a transition metal-free domino addition/cyclization process, the reactions of unsymmetrical carbodiimides with propargylic amines mediated by Cs₂CO₃ selectively afforded the corresponding polysubstituted 2-aminoimidazoles in moderate to good yields under very mild conditions. The regioselectivity was reversed in the presence of TEA at a higher temperature. The obtained 2-(o-iodoaryl)amino imidazoles could be easily converted to 2-(2-biphenyl)amino imidazole, 2-(o-alkynylphenyl)amino imidazole, benzoimidazo[1,2-a]imidazole and N-(imidazol-2-yl)indole derivatives.     

Practical synthesis and applications of benzoboroxoles

A convenient one-pot synthesis of benzoboroxoles has been developed via the reaction of o-bromobenzyl alcohols with NaH, ⁿBuLi, and B(OⁱPr)₃ followed by acidic hydrolysis. Applications of these benzoboroxoles have been demonstrated in Pd-catalyzed cross-coupling reactions and the protocol has been extended for the synthesis of a chiral benzoboroxole. Exceptionally short synthesis of a potent antifungal agent AN2690 and several of its analogs has also been realized.     

Short synthesis of phenylpropanoid glycosides calceolarioside-B and eutigoside-A

A convenient 4-step synthesis of calceolarioside-B 1 and eutigoside-A 2 in high overall yield is described. The key step involved the regioselective, Me₂SnCl₂-catalyzed O-6 acylation of unprotected 2-phenylethyl-β-d-glucosides 5a–b with cinnamoyl chlorides 6a–b in excellent yields. Acylation at O-6 is selective with the acid chlorides used. This work serves as a model for the convenient synthesis of phenylpropanoid glycosides acylated at O-6.     

The synthesis of N-ethyl-n-butylamine by amines disproportionation

A synthesis of N-ethyl-n-butylamine with simple separation method in a fixed-bed reactor using CuO–NiO–PtO/γ-Al₂O₃ as the catalyst was proposed and investigated. The present catalytic system gave high activity and good selectivity, and the reaction conditions such as temperature and liquid hourly space velocity were optimized. Since no water was generated, the protocol proved to be easy to separate, and N-ethyl-n-butylamine was collected at 110 °C by distillation. The yield and the purity were 60.7 and 99.5 %, respectively.