The stereoselective synthesis of cis-/trans-fused hexahydropyrano[4,3-b]chromenes via Prins cyclization trapping by a tethered nucleophile

A novel intramolecular Prins cyclization of (Z)-2-(5-hydroxypent-2-enyl)phenol with various aldehydes has been achieved using 10 mol% In(OTf)(3) and 30 mol% TsOH to produce the cis-fused hexahydropyrano[4,3-b]chromene derivatives in good yields, while the coupling of (E)-2-(5-hydroxypent-2-enyl)phenol with aldehydes under similar conditions affords the corresponding trans-fused hexahydropyrano[4,3-b]chromene derivatives.     

Iodine catalyzed synthesis of the chromene derivatives in one-pot

Iodine catalyzed one-pot reactions of salicylaldehyde and dimolecular 1 H-indene-1,3(2H)-dione,barbituric acids,4-hydroxycoumarin, or 4-hydroxy-6-methylpyran-2-one were performed and provided a rapid,convenient and general approach to synthesize the chromene derivatives.2-(11-Oxo-10,11-dihydroindeno[l,2-b]chromen-10-yl)-1H-indene-1,3(2H)-diones P1-P4 and 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methylpyrano[4,3-6]chromen-1(10H)-ones P8-P9 were unprecedentedly prepared and structurally identified by NMR and Mass.The confirmation of structure by single crystal X-ray crystallography is reported for P3.     

A general synthesis of 6-H-pyrido[4,3-b]carbazole alkaloids

A general and versatile synthesis of the 6-H-pyrido[4,3-b]carbazole alkaloid ellipticine is described; the approach employs the coupling of an acetanilide with a bromoisoquinoline followed by heterocyclic ring formation to give ellipticine.     

Synthesis and Crystal Structure of 3-Phenyi- 6-（4-methylphenyi）-1,2,4-triazolo[4,3-b]-1,2,4-triazine

1 INTRODUCTION The fused heterocycles bearing 1,2,4-triazine have attracted considerable attention in recent years owing to their biological and pharmaceutical activi- ties[1～3]. The 1,2,4-triazine core is a versatile synthe- tic platform to access a wide range of condensed heterocyclic ring systems via inter- and intramolecu- lar Diels-Alder reaction with a vast array of dieno- philes[4～6]. IBD (iodobenzene diacetate) is commer- cially available and used as benign non-metallic oxidant…     

3,3-(Butane-1,4-diyl)bis(1,2-dimethyl-1H-imidazole-3-ium)bromide–cerium(IV) ammonium nitrate: A novel reagent for mild synthesis of 12-aryldibenzo[i,b]pyrano[4,3-b]chromenone of benzyl alcohols

Russian Journal of General Chemistry - A novel and efficient procedure for the synthesis of pyrano[4,3-b]chromene derivatives via three-component condensation reaction of benzyl alcohol,...     

Synthesis and structural characterization of a novel dinuclear complex compound formed by the aerial oxidation of cobalt(II) having an interligand C-C sigma-bond

The aerial oxidation of cobalt(II) salt, in a methanolic solution, containing a hydrazone ligand, (E)-N'-(4-oxo-4-phenylbutan-2-ylidene)benzohydrazide (condensation product of benzoyl acetone and benzhydrazide, LH2) leads to the coupling of two such ligand units through the formation of a rather long C-C bond [1.601(6) A] giving rise to a dinuclear Co (III) hydrazone complex, [Co2(L)2(L')(].0.25H2O (L' = C-C coupled hydrazone ligand). The structure of the complex has been determined by X-ray crystallography and IR, UV-Vis spectroscopy and elemental analysis have characterized the complex.     

Reactions of ethyl 4-amino-6-(ethoxycarbonylmethyl)-2-phenylpyrimidine-5-carboxylate with hydrazines

New substituted 4,6-diamino-7-hydroxypyrido[4,3-d]pyrimidin-5(6H)-ones were synthe-sized by treatment of ethyl 4-amino-6-(ethoxycarbonylmethyl)-2-phenylpyrimidine-5-car-boxylic acid with hydrazine hydrate and phenylhydrazine. In the case of methylhydrazine, the reaction proceeded in an unusual way and afforded a product identified, relying on NMR data, as functionally substituted 8-(5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-7-ylidene)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine comprising two amineimide fragments. A diacetyl derivative of this compound was obtained.     

The mechanism of unimolecular decomposition of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. A computational DFT study

By using the B3LYP level of density functional theory, possible decomposition reaction pathways of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) in the gas phase have been investigated. We have found several types of reactions for this process: homolytic cleavage of an N-N bond to form the NO2* group; HONO elimination; C-C and C-N bonds breaking leading to ring opening; and H-migration. On the basis of the results of computation scanning of the potential energy surface, the most favorite pathway of CL-20 unimolecular decomposition that results in the formation of the stable aromatic compound 1,5-dihydrodiimidazo[4,5-b:4',5'-e]pyrazine has been proposed.     

Sequential approach to the synthesis of 'U and Z' shaped polycyclic heteroarenes

The synthesis of three new classes of heteroarenes, built through the sequential fusion of naphthalene, benzo/naphtho[b]oxepine and thiochromene rings with pyran and pyrimidine ring systems to give 'U and Z' shaped structural frameworks is reported. The methodology is based on the synthesis of pyran fused intermediates, 1-methylthio-3-oxo-5,6-dihydro-3H-benzo[f]chromene-2-carbonitrile (3), 4-methylthio-2-oxo-5,6-dihydro-2H-benzo/naphtho[b]pyrano[2,3-d]oxepine-3-carbonitriles (10, 20) and 4-methylthio-2-oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles (15) from the reaction of 2-tetralone, benzo/naphtho[b]oxepin-5-ones and thiochromen-4-ones with methyl 2-cyano-3,3-dimethylthioacrylate respectively. Further condensation of intermediates 3, 10, 20 and 15 with amidines led to the formation of tetracyclic 'U' shaped 4-amino-2-aryl-7,8-dihydro-5-oxo-5H-naphtho[2,1-b]pyrimido[4,5-d]pyrans (8) and 'Z' shaped 4-amino-2-aryl-5-oxo-12,13-dihydro-5H-benzo/naphtho[b]oxepino[5,4-b]pyrimido[4,5-d]pyrans (12, 22) and 4-amino-2-aryl-5-oxo-5,12-dihydrothiochromeno[4,3-b]pyrimido[4,5-d]pyrans (17). Compound 12f forms a chain of dimers through N-HO interactions as indicated by the X-ray structure analysis, and the quantum chemical calculations performed at the MP2 level indicate that this interaction energy is 10 kJ mol(-1).     

Synthesis of 3-methyl-6-r-6h-thiazolo-[4,3-<Emphasis Type="Italic">b</Emphasis>]-1,2,4-triazolo[4,3-<Emphasis Type="Italic">d</Emphasis>]-1,3,4-thiadiazoles

A one-reactor method has been developed for the synthesis of 3-methyl-6-R-6H-thiazolo[4,3-b]-1,2,4-triazolo[4,3-d]-1,3,4-thiadiazoles by the condensation of aromatic aldehydes, thioglycolic acid, and 4-amino-5-methyl-1,2,4-triazole-3(2H)-thione in a sulfuric acid medium.     

Scope of stereoselective Mn-mediated radical addition to chiral hydrazones and application in a formal synthesis of quinine

Stereocontrolled Mn-mediated addition of alkyl iodides to chiral N-acylhydrazones enables strategic C-C bond constructions at the stereogenic centers of chiral amines. Applying this strategy to quinine suggested complementary synthetic approaches to construct C-C bonds attached at the nitrogen-bearing stereogenic center using multifunctional alkyl iodides 6a-d as radical precursors, or using multifunctional chiral N-acylhydrazones 26a-d as radical acceptors. These were included among Mn-mediated radical additions of various alkyl iodides to a range of chiral N-acylhydrazone radical acceptors, leading to the discovery that pyridine and alkene functionalities are incompatible. In a revised strategy, these functionalities are avoided during the Mn-mediated radical addition of 6d to chiral N-acylhydrazone 22b, which generated a key C-C bond with complete stereochemical control at the chiral amine carbon of quinine. Subsequent elaboration included two sequential cyclizations to complete the azabicyclo[2.2.2]octane ring system. Group selectivity between two 2-iodoethyl groups during the second cyclization favored an undesired azabicyclo[3.2.1]octane ring system, an outcome that was found to be consistent with transition state calculations at the B3LYP/6-31G(d) level. Group differentiation at an earlier stage enabled an alternative regioconvergent pathway; this furnished the desired azabicyclo[2.2.2]octane ring system and afforded quincorine (21b), completing a formal synthesis of quinine.     

Non-catalytic approach to the synthesis of partially reduced 'S' shaped dioxathia- and oxadithiahelicenes through base induced inter- and intramolecular C-C bond formation

An efficient and convenient route for the construction of helical 'S' shaped dioxathia- and oxadithiahelicenes with oxygen and sulfur atoms located in the middle of the outer helix has been developed through base induced inter- and intramolecular C-C bond formation from the reaction of 4-sec-amino-2-oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles with 3,4-dihydro-2H-benzo[b]oxepin-5(2H)-ones, 3,4-dihydrobenzo[b]thiepin-5(2H)-one and thiochroman-4-ones separately. Quantum chemical calculations have also been carried out to explore the geometries and electronic structures of newly synthesized compounds to envisage the pathway for interconversion of both atropisomers. The determination of helicity parameters and configurational stability demonstrate that the energy barrier is strongly dependent on the nature of hetero-atoms present.     

N,N'-双-三唑甲基-[2,2]的合成及晶体结构

标题化合物由N,N′-双-甲氧基甲基_[2,2]和1H_1,2,4-三唑在无溶剂的情况下反应得到。它的单晶X射线分析表明晶体属正交晶系,空间群为Pca2_1,晶胞参数:a=9.986(3)、b=12.932(6)、c=17.135(6)A,z=4。结构用直接法解出,经块矩阵最小二乘法修正,最后的R=0.042。该冠醚环的C—C、N—C与O—C的平均键长分别为1.50(1)、1.40(1)、1.43(1)A,三唑(a)与(b)的五个键长的平均值皆为1.33(1)A。     

Synthesis of dihydrodiol metabolites implicated in the mechanism of carcinogenesis of phenanthro[4,3-b][1]benzothiophene and phenanthro[3,4-b][1]benzothiophene,the polycyclic sulfur heterocycles with a "Fjord" structure

Dihydrodiols, which are potential proximate carcinogens of phenanthro[4,3-b][1]benzothiophene (3) and phenanthro[3,4-b][1]benzothiophene (4) and possess a "fjord" structure, were synthesized. The dihydrodiols synthesized were trans-3,4-dihydroxy-3,4-dihydrophenanthro[4,3-b][1]benzothiophene (5) and trans-3,4-dihydroxy-3,4-dihydrophenanthro[3,4-b][1]benzothiophene (6). The precursors to the dihydrodiols 5 and 6 were 3-methoxyphenanthro[4,3-b][1]benzothiophene (11) and 3-methoxyphenanthro[3,4-b][1]benzothiophene (16). Compound 11 was obtained via Suzuki cross-coupling reaction of easily accessible starting materials. However, this synthetic strategy utilizing Suzuki reaction for the preparation of 16 was comparatively less productive than that described previously due to time-consuming synthesis of the starting material(s), and extremely poor yield associated with cyclization of the epoxide 15 to 16. The methoxy derivatives 11 and 16 were converted to the corresponding dihydrodiols 5 and 6 by a sequence involving demethylation, oxidation, and reduction. The trans-stereochemistry of the dihydrodiols was established by (1)H NMR, which indicated a large coupling constant between vicinal carbinol protons. The UV spectra of the dihydrodiols 5 and 6 are presented.     

The synthesis and crystal structures of halogenated tolans p-X-C6H4-C[triple bond]C-C6F5 and p-X-C6F4-C[triple bond]C-C6H5(X=F, Cl, Br, I)

A series of halogenated, partially fluorinated tolans of general formula p-X-C6H4-C[triple bond]C-C6F5[X=I (1), Br (2), Cl (3), F (4)] and p-X-C6F4-C[triple bond]C-C6H5[X=I (5), Br (6)] have been prepared via palladium-catalysed Sonogashira cross-coupling, or for X=Cl (7), by nucleophilic aromatic substitution reactions. The single-crystal X-ray structures of 1-3 and 5-6 have been determined. The structures reveal that the molecular packing is characterized by either arene-perfluoroarene interactions (3), or halogen-halogen interactions (isomorphous 1 and 2), or neither (isomorphous 5 and 6). The structure of represents the first fully determined crystal structure of a compound that contains a halogen atom other than fluorine, in which arene-perfluoroarene interactions are present.     

Domino carbocationic cyclization of functionalized cyclopropyl ketones: facile one-pot access to peri- and angularly fused polycyclic aromatic and heteroaromatic frameworks

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.     

Air-stable, convenient to handle Pd based PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation) themed precatalysts of N/O-functionalized N-heterocyclic carbenes and its utility in Suzuki-Miyaura cross-coupling reaction

Several new air-stable, convenient to handle and easily synthesized Pd based PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) type precatalysts supported over N/O-functionalized N-heterocyclic carbenes (NHC) namely, trans-[1-(benzyl)-3-(N-t-butylacetamido)imidazol-2-ylidene]Pd(pyridine)Cl2 (), trans-[1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene]Pd(pyridine)Cl2 () and trans-[1-(o-methoxybenzyl)-3-(t-butyl)imidazol-2-ylidene]Pd(pyridine)Br2 (), have been designed. Specifically, the Pd-NHC complexes, , and , were conveniently synthesized from their respective imidazolium halide salts by the reaction with PdCl2 in pyridine in presence of K2CO3 as a base. A new imidazolium chloride salt, 1-(benzyl)-3-(N-t-butylacetamido)imidazolium chloride () was synthesized by the alkylation reaction of benzyl imidazole with N-t-butyl-2-chloroacetamide. The molecular structures of the imidazolium chloride salt, , and the Pd-NHC complexes, , and , have been determined by X-ray diffraction studies. The density functional theory studies of the , and complexes were carried out to in order to gain insight about their structure, bonding and the electronic properties. The nature of the NHC-metal bond in these complexes was examined using Charge Decomposition Analysis (CDA), which revealed that the N-heterocyclic carbene ligands are effective sigma-donors. In addition, the catalysis studies revealed that the Pd-NHC complexes, , and , are effective catalysts for the Suzuki-Miyaura type C-C cross-coupling reactions.     

C-C bond insertion of a complexed phosphinidene into 1,6-methano[10]annulene

Reaction of electrophilic phosphinidene complex [MePW(CO)5] with 1,6-methano-[10]annulene results in the sole formation of the isomeric C-C insertion products 6 c (main) and 6 d (minor). The single-crystal X-ray structure of the complexed 1,7-methano-3-phospha[11]annulene (6 c) shows a syn-W(CO)5 group at the exo bent phosphorus. The structure displays C-C bond alternation without bonding between the bridgehead carbon atoms. Density functional theory calculations indicate 6 c to result from a concerted disrotatory ring opening of an undetected tricyclic exo-syn phosphirane intermediate. The endo-anti phosphirane cannot undergo ring expansion, due to the high barrier that is associated with an intramolecular antara-antara retro Diels-Alder reaction. The stabilizing effect of transition-metal coordination is discussed.     

Synthesis of Some 3-Substituted 1,2-Dihydroindoles

The reaction of 4-oxo-2-(2-oxo-1,2-dihydroindol-3-ylidene)hydrazone-1,3-thiazin-6-methyl carboxylate 2 with hydrazine hydrate in methanol gave 4-oxo-2-(2-oxo-1,2-dihydroindol-3-ylidene)hydrazone-1,3-thiazin-6-carbonylhydrazine 3. Furthermore, the reaction of 3 with carbon disulfide and then hydrazine hydrate afforded 3-[6-(4-amino-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-3-yl)-4-oxo-1,3-thiazin-2-yl] hydrazone-1,3-dihydroindol-2-one 5. the latest reacted with DMAD to give {6-hydroxy-3-[4-oxo-2-(2-oxo-1,2-dihydroindol-3-ylidene)hydrazone-1,3-thiazin-6yl]-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-7-ylidene}methoxycarbonylmethylene 6.     

Unexpected C-C bond cleavage of epoxide motif: rhodium(I)-catalyzed tandem heterocyclization/[4+1] cycloaddition of 1-(1-alkynyl)oxiranyl ketones

A rhodium(I)-catalyzed tandem heterocyclization and formal [4+1] cycloaddition of 1-(1-alkynyl)oxiranyl ketones was developed, which provides a general, efficient and practical route to highly substituted furo[3,4-b]furan-3(2H)-ones, wherein the epoxide motif undergo unexpected C-C bond cleavage rather than the classical C-O bond cleavage.