Fluorinated heterocyclic compounds: an assay on the photochemistry of some fluorinated 1-oxa-2-azoles: an expedient route to fluorinated heterocycles

Photoinduced heterocyclic rearrangements of ON bond-containing azoles have been claimed in the synthesis of target fluorinated heterocyclic compounds. In this context, the photochemical behavior of some fluorinated 1,2,4-oxadiazoles has been investigated. Irradiations of 3-amino-5-perfluoroalkyl-1,2,4-oxadiazoles at λ=313 nm in methanol gave open-chain products arising from a reaction of the nucleophilic solvent with either the first formed ring-photolytic species or with a nitrilimine moiety generated from it. Differently, irradiations in methanol with the presence of triethylamine (TEA) followed competing phototransposition pathways leading to the ring-isomers 2-amino-5-perfluoroalkyl-1,3,4-oxadiazoles (major component) and the ring degenerate isomers 5-amino-3-perfluoroalkyl-1,2,4-oxadiazoles (minor component). On the other hand, 3-amino-5-polyfluorophenyl-1,2,4-oxadiazoles underwent ring-photoisomerization into 1,3,4-oxadiazoles when irradiations were carried out at λ=254 nm. In turn, the irradiation of the 3-phenyl-5-perfluoroheptyl-1,2,4-oxadiazole at λ=254 nm in methanol gave the solvolysis product, but no ring-isomerization was observed. Some mechanistic considerations are reported, and some applications in the synthesis of target fluorinated 1,3,4-oxadiazoles are claimed.     

Fe3O4@SiO2@D-NHCS-Tr as an efficient and reusable catalyst for the synthesis of indol-3-yl-4H-chromene via a multi-component reaction under solvent-free conditions

Fe₃O₄@SiO₂@D-NHCS-Tr was used as an efficient catalyst in the three-component reaction between indole derivatives, salicylaldehyde, and active methylene compounds under solvent-free conditions to the synthesis of indol-3-yl-4H-chromene derivatives. The features of this method include the green conditions of the reaction, easy separation, eco-friendly and cost-effectiveness of the catalyst, and high yield in short reaction times.     

Electronic control of the regiochemistry in the Heck reaction

The migratory insertion of propene into the Pd-phenyl bond of a set of neutral palladium(II) complexes with N-N, P-O, and N-O chelating ligands has been investigated by using density functional methods. In contrast to cationic palladium(II)-diimine complexes, which favor 1,2-insertion, the more electron-rich neutral complexes lead to 2,1-insertion. Trans influences are substantial in the unsymmetrical ligand systems, primarily affecting the insertion barrier. Introducing steric effects leads toward improving 1,2-selectivity, due to destabilization of the 2,1-transition state. Electronic and steric influences can be systematically combined to control the regiochemistry in the Heck reaction.     

Synthesis of 3‐Substituted Benzpyrid‐4‐imino‐2‐oxime Derivatives

Pyrazolone, Isoxazolone, Pyrimidinone, Pyrimidinothione, thiazolidinone and β‐lactam incorporating 2‐oximino benzpyrid‐4‐one derivatives have been synthesized by cyclocondensation addition reaction and cycloaddition of hydrazine hydrate, phenyl hydrazine, hydroxylamine, urea, thiourea, mercapto acetic acid, and chloroacetylchloride, respectively.     

The Mitsunobu reaction in the chemistry of nitrogen-containing heterocyclic compounds. The formation of heterocyclic systems (review)

Methods for the design of nitrogen-containing heterocyclic systems involving the formation of C-N bonds under the conditions of the Mitsunobu reaction are discussed. Dedicated to Afanasi Andreevich Akhrem on his 95th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 347–385, March, 2008.     

Asymmetric gamma-deprotonation and homoaldol reaction of 1,3-dien-2-yl carbamates: stereo- and regiochemistry

[reaction: see text] Lithium compounds 7 are configurationally stable intermediates obtained by deprotonation of 1,3-dien-2-yl carbamates 6 with n-butyllithium/(-)-sparteine with a high degree of enantiotopic differentiation at the gamma-position. They react with electrophiles regioselectively giving highly enantioenriched products. Starting with different isomers or changing the double-bond geometries in 6 leads to either of the enantiomers.     

Generation of an N→B Ladder‐type Structure by Regioselective Hydroboration of an Alkenyl‐Functionalized Quaterpyridine

An unusual reactivity of 2‐(1‐alkenyl)‐pyridines towards hydroboration with 9H‐borabicyclo[3.3.1]nonane (9H‐BBN) has been employed to selectively introduce two borane groups into a conjugated quaterpyridine. Quantitative conversion of the substrate was observed with exclusive regioselectivity. A molecular structure that allows intramolecular N→B coordination was generated. The effect of the ladder formation on the molecular structure and the electronic properties of the conjugated system have been investigated. The synthetic strategy demonstrated herein offers a facile access to N→B ladder‐type structures from readily available substrates, and allows to simultaneously introduce several boron centers under mild conditions.     

Heck-mediated synthesis and photochemically induced cyclization of [2-(2-styrylphenyl)ethyl]carbamic acid ethyl esters and 2-styryl-benzoic acid methyl esters: total synthesis of naphtho[2,1f]isoquinolines (2-azachrysenes)

We describe two new closely related total syntheses of naphtho[2,1-f]isoquinolines. The first synthesis consists of a Heck coupling reaction between trifluoromethanesulfonic acid 2-(2-ethoxycarbonylaminoethyl)phenyl esters and styrenes to give [2-(2-styrylphenyl)ethyl]carbamic acid ethyl esters. These compounds cyclize to give (2-phenanthren-1-yl-ethyl)carbamic acid ethyl esters, from which 2-azachrysenes can be obtained in a three-step sequence. The second synthesis includes a new total synthesis of 2-styrylbenzoic acid methyl esters by Heck coupling of methyl o-iodobenzoates to styrenes, followed by the transformation of the resulting benzoic acid derivatives into phenanthrene-1-carboxylic acid methyl esters and then into the target compounds by a six-step sequence including a Bischler-Napieralski cyclization.     

New methodology for the N-alkylation of 2-amino-3-acylthiophenes

2-Amino-3-acylthiophenes are known to allosterically modulate the A(1) adenosine receptor and are also used as intermediates in the synthesis of therapeutic agents and pharmacophores such as thienoazepines and thienopyrimidines. The N-alkylation of 2-aminothiophenes has been notoriously difficult to accomplish under mild conditions and there are very few examples of N-alkylated 2-aminothiophenes in the literature, all of which use forcing conditions to effect the alkylation. Here we describe the synthesis of such compounds under mild conditions utilising 2-carbamoylamino and 2-acylamino-3-acylthiophenes with caesium carbonate, and tetrabutylammonium iodide in DMF.     

The effect of the trimethylsilyl group on the regiochemistry of the ene reaction

The trimethylsilyl group has been found to have a profound effect on the regiochemistry of the ene reaction of E-1-methyl-2-trimethylsilyl olefins during the formation of [3.3.0] bicyclo-octanes.     

6,7-二氧亚甲基-3-硫杂-1(2H,4H)吖啶酮的Beckmann重排及硫杂吖啶并六员杂环的合成

吖啶类化合物是一类颇受人们注意的抗疟药物,具有抗癌活性的吖啶合成也引起了有机化学工作者的极大兴趣。虽然对吖啶的化学已经进行了相当深入的研究,但硫杂吖啶酮     

Gaining absolute control of the regiochemistry in the cobalt-catalyzed 1,4-hydrovinylation reaction

The absolute control of the regiochemistry of a cobalt-catalyzed 1,4-hydrovinylation reaction is achieved by alternation of the ligands applied. While the dppe/dppp ligands led to the formation of the branched product, the herein described application of the SchmalzPhos ligand generates the corresponding linear product in both excellent yields and regioselectivities. The catalyst system exhibits a high tolerance toward functional groups, and the very mild reaction conditions allow the synthesis of 1,4-dienes without isomerization into conjugated systems.     

Reaction of 2-arylhydrazono-2-cyano-N-cyclohexylthioacetamides with halocarbonyl compounds

The reaction of arylhydrazonocyanothioacetamides containing an N-cyclohexyl fragment with chloroacetone, phenacyl bromide, ethyl chloroacetate, and chloroacetonitrile was investigated. It was shown that a substituent with a large steric effect in the thioamide group alters the direction of intramolecular cyclization of the thioimidate intermediate. In contrast to the Hantsch reaction, which usually leads to the formation of thiazoles under these conditions, the only products are 3-amino-4-arylhydrazono-4,5-dihydrothiophenes. Dedicated to Prof. Dr. E. Lukevics on his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 22–33, January, 2007.     

First N‐Heterocyclic Carbenes Relying on the Triazolone Structural Motif: Syntheses,Modifications and Reactivity

4‐Phenylsemicarbazide and 1,5‐diphenylcarbazide are suitable starting materials for the syntheses of N‐heterocyclic carbene (NHC) compounds with new backbone structures. In the first case, cyclisation and subsequent methylation leads to a cationic precursor whose deprotonation affords the triazolon‐ylidene 2 , which was converted to the corresponding sulfur and selenium adducts and a range of metal complexes. In contrast, cyclisation of diphenylcarbazide affords a neutral betain‐type NHC‐precursor 7 , which is not in equilibrium with its carbene tautomer 7a . Precursor 7 can either be deprotonated to give the anionic NHC 8 or methylated at the N or O atom of the backbone resulting in two isomeric cationic species 16 and 20 . Deprotonation of the latter two provides neutral NHC compounds with a carboxamide or carboximidate backbone, respectively. The ligand properties of the new NHC compounds were evaluated by IR and ⁷⁷Se NMR spectroscopy. Tolman electronic parameter (TEP) values range from 2050 to 2063 cm^?1 with the anionic NHC 8 being the best overall donor.     

Unusual condensation ofN-phenylsemiquinonediimine ligands coordinated to the NiII atom with an acetone molecule to form a heterocycle

The reaction of a mononuclear Ni^II semiquinonediimine complex,viz., Ni[1,2-(NPh)(NH)C₆H₄]₂, with silver triflate was investigated. The starting monomer was not oxidized in benzene or CH₂Cl₂ solutions; instead, a solvate of the complex with C₆H₆ was formed. According to the X-ray diffraction data, the solvate is characterized by an unusual molecular packing with short C−H(C₆H₆)... Ni and C−H(C₆H₆)... N−H contacts. An analogous effect is observed in the crystals of the solvate Pt[1,2-(NPh)(NH)C₆H₄]₂·C₆H₆. Grinding of the nickel complex with silver triflate (the reagent ratio was 1:5) in the presence of acetone led to the oxidation of the complex, yielding tetrahydroimidazophenazinium triflate, whose structure was established by X-ray diffraction analysis. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1794–1798, October, 2000.     

Multifaceted Behavior of 2-Cyanobenzaldehyde and 2-Acylbenzonitriles in the Synthesis of Isoindolinones,Phthalides and Related Heterocycles

2-Cyanobenzaldehye (also called 2-formylbenzonitrile) and related 2-acylbenzonitriles belong to a class of bifunctional aromatic compounds that emerged as useful starting materials in developing efficient cascade-type reactions leading to different heterocyclic compounds. The variety of sometimes unpredictable mechanisms that rise from these structurally simple starting materials renders this class of compounds unique to afford, through divergent cascade reactions, heterocycles like isoindolinones, phthalides (also known with the name of isobenzofuranones), imidates, and in less extent isoindolin-1-imine, six- and seven-membered heterocycles, porphyrins, also in asymmetric way exploiting different organocatalytic activation modes. To give a picture, this chemistry can be associated to Goldberg variations which stem from a common motive in a pressing and surprising way. In this Review, emphasis is also given to the synthetic methods for the access to substituted 2-cyanobenzaldehydes and 2-acylbenzonitriles which allowed to enlarge the scope of the described cascade reactions.