Enantioselective synthesis of herbertane sesquiterpenes: synthesis of (−)-α-formylherbertenol

The synthesis of 4-hydroxy-3-[(1S)-1,2,2-trimethylcyclopentyl]benzaldehyde [(−)-α-formylherbertenol 1], a herbertane-type sesquiterpene isolated from the leafy liverwort Herberta adunca, from β-cyclogeraniol is described. The synthesis is based on the previously described preparation of an enantiopure 1,2,2-trimethylcyclopentane synthon from which the characteristic aromatic moiety of 1 is elaborated, using a Robinson annulation and a palladium-catalysed methoxycarbonylation of an aryl triflate as key synthetic steps. The synthesis of the natural sesquiterpene (−)-α-herbertenol, also a natural sequiterpene, using the same methodology is also described.     

Selective synthesis of β-alkylpyrroles

β-Alkylpyrroles are key structural motifs found in many natural products and biologically active compounds as well as functional organic materials. For this reason, synthetic chemists continue to be interested in construction of the framework of β-alkylpyrroles. Due to sufficient aromaticity and π-excessive nature of pyrroles, a straightforward approach to β-alkylpyrroles should be electrophilic aromatic substitution (S(E)Ar) toward the pyrrole ring. However, since a primary nucleophilic site of pyrroles is an α-position, some "trick" is required to direct incoming alkyl electrophiles toward a β-position. This Concept article focuses on presenting previous efforts that have been devoted to the synthesis of β-alkylpyrroles, mainly through the S(E)Ar route.     

A novel synthesis of perfluoroalkylglycine

Perfluoroalkylglycine was obtained through perfluoroalkylation of 2-phenyl-5-etho-xyoxazole using RFI-Na2S2O4 reagent system, followed by acid hydrolysis of the intermediates, 2-phenyl-4-perfluoroalkyl-5-ethoxyoxazole and 2-phenyl-4-perfluoroalkyl-2-oxazolin-5-one.     

Total synthesis of (−)-vindoline

In this full paper, a stereocontrolled strategy for the total synthesis of (?)-vindoline is described. This synthetic route features: 1) rapid construction of the stereochemical center at C19 through a highly diastereoselective vinylogous Mannich addition; 2) tandem Heathcock/aza-Prins cyclization to install rings C and E in vindoline; 3) oxidative transformation of β-ketoester to enone; 4) stereoselective inversion of C4 stereochemistry with triphenylphosphine and carbon tetrabromide followed by Brønsted acid.     

Enantioselective synthesis of β-amino-diacids

An efficient route to orthogonally protected β-amino-diacids is described: chiral derivative 3 was shown to be a precursor of enantiopure substituted β-amino acids. The key step of the procedure is a diastereoselective reduction of β-enaminolactones 5 by NaBH₃CN in CH₂Cl₂. A study concerning the regio- and diastereoselectivity of alkylation of β-enaminolactone 3 is also presented.     

Stereoselective synthesis of α-C-glycosides of N-acetylgalactosamine

Attempts to synthesise α-C-glycosides of N-acetylgalactosamine by selective deprotection at C-2′ of allyl α-C-galactoside 1 and subsequent amination failed, but opened the way to α-C-talopyranosides. The synthesis of α-C-glycosides of N-acetylgalactosamine was performed from allyl α-C-glucopyranoside 9, which was regioselectively deprotected, stereoselectively aminated at C-2′, and finally epimerised at C-4′.     

Solvent-free synthesis of zeolite catalysts

The most used method for preparation of zeolites is hydrothermal synthesis from silicate or aluminosilicate gels at temperatures in the range of 60–200°C.Excess water used in the industrial process results in several issues,including high autogeneous pressure,low efficiency,pollution,etc.To solve these problems,several strategies have been developed.This review describes the solvent-free synthesis of zeolites.The combination of solvent-free synthesis and organotemplate-free synthesis can open the pathway to a highly sustainable zeolite synthesis protocol in industry.     

One-pot synthesis of β-imidazolylpropionamides

New efficient one-pot methodology for the preparative synthesis of β-imidazolylpropionamides was elaborated. It is based on the addition of imidazole to the activated double bond of the intermediate acrylimidazolide in the reaction between diverse acrylic acids and different amines promoted by CDI. A set of structurally and functionally diverse β-imidazolylpropionamides was obtained in high preparative yields.     

Total synthesis of (−)-lentiginosine

A simple and practical synthesis of (−)-lentiginosine 2 with good overall yield has been achieved from the commercially available diethyl d-tartarate. The key steps are a highly stereoselective Grignard reaction on an aldehyde and a Staudinger reduction.     

The synthesis of perfluoroalkyl-substituted tetrakisphenylporphyrins

Perfluoroalkyl-substituted tetrakisphenylporphyrins were synthesized through the couplingreaction of perfluoroalkyl iodides(R_FI)with the corresponding bromophenylporphyrin under theCu-bronze catalysis.     

Stereoselective synthesis of (−)-cytoxazone

A novel stereoselective synthesis of (−)-cytoxazone 1 was achieved via addition of p-methoxyphenylmagnesium bromide to the benzylimine derived from (S)-2,3-O-isopropylidene glyceraldehyde followed by one-step regioselective cyclization of N-Boc amino diol 7.     

Optimization of process parameters of γ-polyoxymethylene synthesis

Two procedures for γ-polyoxymethylene production are considered: the existing commercial procedure and high-efficiency perspective procedure, differing in the chain-transfer agents and catalysts used. Mathematical models of the dependences of the yield and weight-average particle size of γ-polyoxymethylene on the synthesis process parameters for the commercial and perspective technologies are constructed using the method of optimum experiment design. The mathematical models were used for determining the optimum synthesis parameters allowing preparation of γ-polyoxymethylene with the weight-average particle size d ≤ 14 μm in maximal yields.     

Metal-free synthesis of amphiphilic functional polycarbonates

Amphiphilic block copolymers of poly(5-benzyloxy trimethylene carbonate)(PBTMC) and poly(ethylene glycol)(PEG) were synthesized through enzymatic polymerization using immobilized porcine pancreas lipase(IPPL).The obtained copolymers with different compositions were characterized by GPC and ~1H NMR.The copolymer composition was in agreement with the feed ratio. The molecular weight of the copolymers showed an increasing trend with the decrease of PEG contents.Micelles of the copolymers were formed by dialysis procedure,and characterized by transmission electron microscopy (TEM).     

A convenient synthesis of 6-demethoxycapillarisin

A convenient and effective method for the synthesis of 6-demethoxycapillarisin was described.The highlight was involved in asimple access to the key intermediate 2-ethylthio-5,7-dimethoxy-4H-chromen-4-one from the inexpensive 2,4,6-trihydroxyacetophenone,using AlCl3 as the demethylation reagent.     

Microwave-assisted synthesis of dialkyl ω-azidoalkylphosphonates

An efficient and reproducible microwave-assisted synthesis of dialkyl ω-azidoalkylphosphonates via nucleophilic substitution of the appropriate dialkyl ω-bromoalkylphosphonates by sodium azide in water or dimethylformamide (DMF) as solvent has been developed. This process has been optimized for batch reactors. The target, structurally diverse dialkyl ω-azidoalkylphosphonates with different steric hindrance around the phosphonato groups and containing unbranched side carbon chains of different lengths (n?=?2–6), has been obtained in moderate to high yields (39–87%).     

Large-scale synthesis of α-amino acid-N-carboxyanhydrides

Hetero- and homopolymers prepared from α-amino acid-N-carboxyanhydrides (NCAs) monomers are widely useful products. The preparation of pure NCA monomers has been extensively studied in the past. Purification methods including repeated crystallizations, extraction, and flash column chromatography have been devised. However, these methods are not easily amendable to large-scale NCA preparations. This article describes the synthesis of numerous highly purified NCAs on a >100?g scale using a simple filtration step through diatomaceous earth (celite). The resulting NCAs provided polyethylene glycol (PEG)–amino acid triblock polymers devoid of low-molecular-weight by-products that were routinely observed when unfiltered batches of NCAs were used. Also disclosed is the preparation of NCAs at ambient temperature. Traditionally, NCA reactions using a phosgene source are heated. This study shows these reactions can be driven by the slight exotherm that forms upon reagent mixing. This eliminates the need for an external heating source, simplifying large-scale reactions.     

Asymmetric synthesis of α-acetylenic epoxides

Chiral α-acetylenic oxiranes were easily synthesized from readily available propargylic esters by a four-step sequence involving the stereoselective reduction of α′-alkynyl β-keto sulfoxides with DIBAH (de 66–78%) and DIBAH/ZnBr₂ (de 78–88%), followed by further reduction of the resulting hydroxy sulfoxides into the corresponding sulfenyl derivatives and final epoxy ring closure via sulfonium salt.     

Stereoselective synthesis of a β-D-phosphatidylgalactose

The stereoselective synthesis of a -D-phosphatidylgalactose has been achieved by the interaction of a benzyl phosphatidate with D-galactose tert-butyl orthoacetate or trichloroacetimidate.M. V. Lomonosov Institute of Fine Chemical Technology, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 16–19, January–February, 1991.     

Microwave synthesis of α-cyano chalcones

A novel methodology for facile production of α-cyano chalcones under microwave irradiation is described. Utilizing a Knoevenagel condensation between benzoylacetonitriles and aromatic aldehydes, substituted chalcones are generated via a 15-min, one-pot synthesis. Diversification of aromatic groups, including electron-withdrawing, electron-donating, and heterocyclic substitutions, has led to the isolation of over twenty colored, solid chalcone products. Furthermore the methodology can be extended to the synthesis of benzylidenemalononitriles as well as methyl and ethyl α-cyano cinnamates.