Design and synthesis of enantiopure 1-[1(S)-(2-pyridyl)alkyl]-2(R)-isopropylaziridines, new ligands for asymmetric catalysis

Enantiopure 1-(2-pyridyl)alkyl aziridines were designed as bidentate ligands for asymmetric catalysis. Their synthesis involved the addition of organometallic reagents to the imine prepared from 2-pyridinealdehyde and an enantiopure β-aminoalcohol, followed by cyclisation of the β-aminoalcohol moiety to the aziridine ring. Two such ligands (N–N)* were prepared from (S)-valinol and converted to the complexes (η³-allyl)(N–N)*Pd⁺SbF₆⁻, one of which was characterised by X-ray crystallography. Modest enantioselectivities were achieved in a representative Pd-catalysed allylic substitution reaction.     

Radical cyclisations of methylenecyclopropyl azetidinones—synthesis of novel tricyclic β-lactams

Addition of lithium bis(methylenecyclopropyl)cuprates to acetoxy azetidinones gives methylenecyclopropyl azetidinones, which can be converted to various radical cyclisation precursors. Attempted 4-exo cyclisation of 3 led only to reduced product, while cyclisation of 5, using CuCl/bipy, gave a carbacephem, via a 5-exo cyclisation, but in low yield. Cyclisation of 6 and 7, however, gave novel tricyclic β-lactams, as the result of 7-endo cyclisation, in good yield, and a cyclisation of bromide 23 led to the tricyclic β-lactam 24, via a radical cascade sequence.     

Metal-free synthesis of 3-chalcogen benzo[b]furans via an iodine-mediated electrophilic cyclisation of 2-alkynylanisoles

An efficient and metal-free method was developed to synthesize 3-chalcogen benzo[b]furans via the iodine-mediated electrophilic cyclisation of 2-alkynylanisoles with disulfides or diselenides. In the presence of I₂, various 3-sulfenylbenzofurans or 3-selenenylbenzofurans were obtained in moderate to high yields.     

Photochemical intramolecular aromatic substitutions of the imidazol-2-yl radical are superior to those mediated by Bu3SnH

Six-membered photochemical cyclisations of 2-iodo-N-(2-arylethyl)imidazoles proceeded regioselectively in higher yields than the equivalent tin hydride-mediated reactions. The decrease in yield of cyclisation products, 5,6-dihydroimidazo[2,1-a]isoquinolines containing strongly deactivating substituents on the aryl ring confirmed the electrophilic nature of the sigma-imidazol-2-yl radicals. The seven-membered cyclisation was only successful under photochemical conditions, as radical reduction occurred with tin hydride. Nitration of 5,6-dihydroimidazo[2,1-a]isoquinoline with nitric/sulfuric acid occurred at the 2- and 8-positions.     

The Bittig Reaction of Benzofuranones

The cyclisation of appropriately substituted bensane derivatives affords 3-alkyl, 3-aryl and 3(2H)-benzofuraones but other 3-Substituted benzofurans are not directly available by ring closure methods or by electrophilic substitution.^2,3 We now report a convenient route to such compounds via the Wittig reaction between 3(2H)-benzofuranones and stable phosphorus ylids.     

Synthetic applications of umpoled vilsmeier reagents - A new simple one-pot route to isatins from formanilides

When N-substituted formanilides are treated briefly and sequentially with oxalyl chloride, Hünig's base, and bromine, isatins are rapidly formed, many in good yields. The reaction involves deprotonation of the Vilsmeier reagent, dimerisation of the carbene thus formed and electrophilic cyclisation of the dimer by bromonium ion action followed by aqueous hydrolysis.     

ESR studies of γ-irradiated histone octamer and the histone H3

ESR spectrum of neat histone H3 γ-irradiated and observed at 77 K with low microwave power and modulation amplitude showed multiple resolved structure depicting nonequivalent interaction of the unpaired electron located at amido-carbonyl radical anion [– )NH–] of the peptide backbone with adjacent –NH– group and the β-proton of –CH group. The predominance of amido-carbonyl radical anion is in good accord with the expected partition of secondary electrons amongst the various electrophilic groups including peptide carbonyl and aromatic acid residues. Following a gradual rise of annealing temperature to room temperature, a double splitting spectrum from the well known -carbon amido radical was evolved.     

Synthesis and transformation of novel cyclic β-amino acid derivatives from (+)-3-carene

The regio- and stereoselective addition of chlorosulfonyl isocyanate to (+)-3-carene 1 resulted in β-lactam 2, which was converted to N-Boc-β-amino acid 4, β-amino ester 7, and carboxamide derivatives 18 and 20 via N-Boc activation and mild ring opening. The corresponding β-amino ester 7 was transformed to 2-thioxopyrimidin-4-one 11 and 2,4-pyrimidinedione 13. LAH reduction of 5 and 7 resulted in amino alcohols 6 and 8. The reaction of 8 with phenyl isothiocyanate, followed by cyclisation, furnished 1,3-oxazine 15.     

An enantiospecific synthesis of (+)-demethoxyerythratidinone from (S)-malic acid: key observations concerning the diastereocontrol in malic acid-derived N-acyliminium ion cyclisations

The stereochemical outcome of N-acyliminium ion mediated cyclisations of malic acid derived lactams depend upon the nature of the protecting group on the lactam secondary alcohol, and also on the nature of the substituent at the reacting electrophilic centre. The origins of an unusual syn-selective cyclisation of a TIPS protected lactam are discussed, and the cyclisation is employed as the key step in an asymmetric synthesis of 3-demethoxyerythratidinone (4).     

Halogenures de tellurenyle—iii: Coupure carbone aromatique-tellure par protodetelluration et carbodetelluration intramoleculaire

In the course of electrophilic cyclisation attempts, o-phenyltellurobenzoyl-chloride did not cyclise to telluroxanthone. but isomerised to 2-chloro tellurobenzophenone through intramolecular carbodetelluration. A breaking of the same C_aromatic-Te bond is also realized by protonolysis. This last reaction leads to a preparative method of synthesis of ditellurosalicylic acid, a starting material for synthesis of benzocondensed tellurium heterocycles.     

A comparative study on the nature and strength of O–O, S–S, and Se–Se bond

A computational study on dichalcogenide molecules (R₂X₂; X = O, S, Se; R = H, CH₃, NH₂) has been carried out employing B3LYP and MP2 levels using 6-31+G*, 6-311+G*, 6-311++G**, and PVDZ basis sets. The relative energies have been evaluated at G2MP2 also. The rotational barriers and bond dissociation energies indicate that S–S bond is stronger than Se–Se and O–O bond. NBO analysis at MP2/6-31+G* suggest the presence of partial π character between X–X bond that decreases in the order S–S > Se–Se > O–O. Fuki functions for nucleophilic and electrophilic attack fail to distinguish the reactivity of S and Se. The proton affinities of the O₂H₂, S₂H₂, Se₂H₂ decrease in the order Se > S > O.     

Isomérisations en chimie des sucres. II Fermetures de cycles par attaque nucléophile intramoléculaire sur des carbones sp2 à caractère électrophile: Furannoses hybridés sp2 en C3

When heated with one equivalent of H₂O, the 1,2: 5,6-di-O-isopropylidene-α-D-ribo- and -xylo-hexofuranos-3-uloses loose one molecule of acetone and yield the 3, 6-anhydro-1, 2-O-isopropylidene-α-D-ribo- and -xylo-hexofuranos-3-ulose ketohydrols. The carbonyl group of the starting material seems to provide some kind of intramolecular electrophilic assistance to the hydrolysis of the 5, 6-O-isopropylidene group. When the oxygen of the carbonyl group is replaced by cyanomethylene, an analogous cyclisation takes place under base catalysis, provided that C6 bears a free hydroxyl group.     

Mittlere ringe-XIII Die intramolekulare acylierung der ω-(1-naphthyl)-fettsäuren

The intramolecular Friedel-Crafts cyclisation of ω-arylalkanoic acids, which is in the benzene series a valuable synthetic route to bicyclic ketones with medium-sized and large rings, has been investigated with ω-(1-naphthyl)alkanoyl chlorides. The lower members, including naphthyl-caproic acid, close the ring at position 2 to form IV. The higher homologous acids show a preference for annellation at 7, making available a new type of heteronuclear naphthalene cyclic ketones (VII). During cyclisation of ω-(1-naphthyl) decanoic acid, the 1,4 ring closure competes with the 1,7 type.

Steric hindrance of resonance as a consequence of “medium ring torsion” was studied in different classes of naphthocyclenones.     

A simple and efficient PdCl2 mediated conversion of γ,δ-olefinic alcohols into C-glycosides

An efficient and mild intramolecular oxidative nucleophilic cyclisation protocol has been developed for the conversion of γ, δ-olefinic alcohols into the hemiketals, which in turn on deoxygenation led to the very important C-glycoside class of compounds.     

Nazarov cyclisation of dienone-esters and tetrahydropyrones using trimethylsilyltriflate

Dienone- and tetrahydropyrone- esters undergo Nazarov-type cyclisation using trimethylsilyltriflate.

Cyclopentenone esters have been synthesized via a Nazarov cyclisation of the corresponding ,′-dienone esters or tetrahydro-γ-pyrone esters employing trimethylsilyltriflate at room temperature. The dienone esters were synthesised by a short two-step acylation-Knoevenagel sequence.     

Une synthese totale stereospecifique de c-nor d-homosteroides comportant six carbones asymetriques

An efficient and stereoselective total synthesis of C-nor D-homosteroid compounds is described, following a general pathway of the A→B→C→D type. The A-B ring system was provided by the Wieland-Miescher ketone . the ring C was formed by intramolecular cyclisation of an appropiate γ-diketone such as . Construction of the ring D was achieved by means of a Birch reductive alkylattion, followed by intramolecular cyclisation of the intermediate δ-diketone thus formed. C-nor D-homosteroids and having six asymmetric carbons as well as the required “natural” configuration were thus obtained in eleven steps from the Wieland-Miescher ketone .     

[3,2] sigmatropic rearrangements of allylic oxosulphonium ylides

The oxosulphonium ylides (1) and (5) react with electrophilic acetylenes to give allylic ylides, which undergo successive [3,2] rearrangement, elimination of methanesulphinic acid, and cyclisation on heating.     

Synthesis of the bicyclic core of tagetitoxin

A synthesis of the 9-oxa-3-thiabicyclo[3.3.1]nonane ring system, which constitutes the core of the RNA polymerase inhibitor tagetitoxin, has been achieved through cyclisation of a thiol onto an electrophilic ketone.     

Supramolecular helical architecture from the self-assemblies of 2-chloro-5-nitro-benzoic acid and organic bases

Assembly of 2-chloro-5-nitro-benzoic acid (CNB) and organic bases containing nitrogen atom, 8-hydroxyquinaldine (purum), 1,2-bis(4-pyridyl)ethane (BPE), and 2-aminobenzimidazole, resulted in novel adducts with helical architecture. We present here an unprecedented single-stranded helix (left-handed and right-handed helices) in adduct 1. The helices are formed via three kinds of hydrogen bonding, O5–H5O1, C11–H11BO3, and C14–H14O1. But the two helices are linked by C9–H9O4 and C11–H11BO3 H-bonds. The interactions result in the cavity with dimensions of 8 × 10.5 Å, respectively. Interestingly, the different single-stranded helical structure in adduct 2 is generated via Cl1O1 interactions, where BPE linking the two helices by C9–H9O1 and O3–H3N2 H-bonds. The ring motifs and novel helical structures observed in the crystal packing suggest for further scopes in exploiting different substituent chloro-nitro-benzoic acid in a predictive manner or capturing useful nanoscale entities for self-assembly.     

Reactions of 2-Nitro- and 2-Bromo-2-nitroethenylphosphonates with Anthracene

Bis(2-chloroethyl) 2-nitro- and 2-bromo-2-nitroethenylphosphonates react with anthracene along two competing pathways: [4+2] cycloaddition and electrophilic substitution; in the case of the bromo derivative, the resulting products undergo dehydrobromination under the reaction conditions to form anthracene- and dihydroanthracene-containing nitroethenylphosphonates.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 729–733.Original Russian Text Copyright © 2005 by Anisimova, Kuzhaeva, Berkova, Deiko, Berestovitskaya.