Reactions of heterocumulenes with organometallic reagents: XIX. Quantum-chemical study on S-alkylation and intramolecular cyclization of lithiated methoxyallene adducts with methyl, phenyl, and 3-(methylsulfanyl)phenyl isothiocyanates. Concurrent formation of pyrrole and/or thiophene rings

Concurrent reaction paths leading to the formation of thiophene and/or pyrrole rings from adducts of lithiated methoxyallene with methyl, phenyl, and 3-(methylsulfanyl)phenyl isothiocyanates were simulated by quantum-chemical methods. According to the calculations, pyrrole ring closure is kinetically more favorable for the adduct of 1-lithio-1-methoxyallene with methyl isothiocyanate, both reaction channels are equally probable for the adduct with phenyl isothiocyanate, and thiophene ring closure is the main reaction path for the adduct with 3-(methylsulfanyl)phenyl isothiocyanate.     

3, 6-endoxocyclohexanes and -cyclohexenes. XXV. Some reactions of dimethyl 4,5-(1-benzyl-1, 2, 3-triazoline)-3, 6-endoxohexahydrophthalate

The anhydride and dimethyl ester of 4, 5-(1-benzyl-1, 2, 3-triazoline)-3, 6-endohexahydrophthalic acid, having a triazoline ring with an exo-cis configuration, are synthesized by reaction of benzyl azide with the furan-maleic anhydride adduct. Opening of the triazoline ring under the action of hydrochloric and acetic acids takes place with the separation of nitrogen and formation of the chloro and acetoxy derivatives, respectively, unaccompanied by a Wagner-Meerwein type of rearrangement.Part XXIV, see [1].     

Furopyridines. XXII. Elaboration of the C-substituents alpha to the heteronitrogen atom of furo[2,3-b] -, -[3,2-b] -, -[2,3-c]- and -[3,2-c]pyridine

The Grignard reaction of fused ring cyanopyridine derivatives 1a-d with methyl- and phenylmagnesium bromide yielded the corresponding acylpyridine compounds 2a-d and 3a-d . Furopyridine N-oxides 4a-d were converted into the compounds having a phenyl group at the α-position to the ring nitrogen 5a-d . Reduction of 1a-d and the carboxylic esters 6a-d with diisobutylaluminium hydride yielded the corresponding amines 7a-d and aldehydes 9a-d . The aldehydes were converted to nitroethanol derivatives 10a-d by condensation with nitromethane and acrylic ester compounds 11a-d by the Wittig-Horner reaction with methyl diethyl phosphonoacetate.     

Deamination,involving ring opening,in reactions of 1-aminopurinium mesitylenesulfonates with methanolic amonia

On reaction of 1-aminopurinium mesitylenesulfonates with methanolec ammonia N-deamintion occurs. For 1-amino-, 1-amino-8-(methylthio)-, 1-amino-8-phenyl-, 1-amino-2-methyl-, 1-amino-6-methyl- and 1-amino-8-phenyl-9-methyl-purinium mesitylenesulfonate this reaction proceeds for at least 75% via ring opening as shown by the isolation of 1-¹⁵N-labelled purines when ¹⁵N-labelled methanolic ammonia was used. 1-Amino-9-methylpurinium mesitylenesulfonate gave N-deamination without ring opening. The reaction of 1-amino-6-(methylthio)purinium mesitylenesulfonate with methanolic ammonia involves, besides deamination, partial substitution of the methylthio group; no ring opening is involved. However, ring opening followed by substitution occurs in the reaction of 1-amino-2-(methylthio)purinium mesitylenesulfonate; the reaction proceeds via an adduct at position 2.     

Structural effects on the beta-scission reaction of alkoxyl radicals. Direct measurement of the absolute rate constants for ring opening of benzocycloalken-1-oxyl radicals

[reaction: see text] The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X = H, Me, whereas exclusive C-X bond cleavage occurs when X = Et. The factors governing the fragmentation regioselectivity are discussed.     

Thermal dissociation of 1,2-dioxethane. II. Quantum topology of the charge distributions

The topological properties of the charge distribution of 1,2-dioxethane along the dissociation path (to formaldehyde products) and in different Hartree–Fock solutions are presented. At the equilibrium geometry of 1,2-dioxethane, all bond paths do not coincide with the corresponding internuclear axes. The outward curvature of the O? O bond path elaborates upon the concept of strain in the dioxethane ring. This weak binding of the ring is further confirmed by the considerably low ρ(r) value at the ring (3, +1) saddle point. An extension of the theory to the dynamic case has been discussed in terms of the topological changes in ρ(r) along the reaction path. The catastrophe of the chemical change, i.e., rupture of the dioxethane ring, takes the form of gradual merging and annhilation of the O? O (3, ?1) and the ring (3, +1) critical points. The values of ρ(r) at the positions of the critical points along the reaction path provide a topological characterization and definition of “partial valence.” The difference between the topological behavior of ρ(r), as obtained by different HF solutions, along the reaction path is analyzed and discussed.     

Studies on the benzo[1,2]cyclohepta[3,4,5-d,e]isoquinoline ring system

The syntheses of various oxidation states of the novel benzo[1, 2]cyclohepta[3, 4, 5-d, e]-isoquinoline ring system is described. The ring system was obtained by the Schmidt rearrangement, with exclusive alkyl migration, of 1, 6, 7, 11b-tetrahydro - 2H - dibenz-[cd,h]azulen-2-one and by a Bischler-Napieralski reaction of suitable derivatives of 10, 11-dihydro-5H-dibenzo[a, d]cycloheptene - 5 - methylamine. 4, 5, 10, 11 - Tetramethoxy derivatives of the new ring system were best prepared by a Pictet-Spengler reaction of the appropriate amine.     

新型双大环二正丁基锡羧酸酯的合成、晶体结构及生物活性

在乙醇钠催化下, 将3-(1,2亚丙二硫基)亚甲基-2,4-二羰基戊烷与2-羰基苯氧乙酸进行缩合反应, 获得了柔性二元酸配体1[4-(1,2-亚丙二硫基)亚甲基-3,5-二羰基-1,6-庚二烯-1,7-二(2-羰基苯)氧乙酸(LH2)]. 再将配体1与二正丁基氧化锡进行脱水反应, 获得新型二正丁基锡羧酸酯配合物2. 采用元素分析、1H NMR、 IR及晶体结构测定等手段对配体1和配合物2进行了结构表征, 配合物2是以菱形环Sn2O2为中心对称的二聚体结构, 中心菱形环通过氧原子与2个环外锡原子相连. 每个羧基分别与环内锡和环外锡原子配位, 形成2个对称的六元环, 3个环呈梯形排列, 将整个分子分割成2个对称的二十二元大环. 初步研究了其杀菌活性和抗癌活性.     

A symmetric derivative of the trimetallic nitride endohedral metallofullerene, Sc3N@C80.

The reaction of Sc3N@C80 with 6,7-dimethoxyisochroman-3-one (13C labeled) provides the first functionalized derivative of the trimetallic nitride template (TNT) endohedral metallofullerene family. The reaction mixture is dominated by a single 13C labeled monoadduct product that was purified by HPLC. The 13C labeled monoadduct was characterized by 1H NMR, 13C NMR, and MALDI-TOF mass spectrometry. The proposed structure for this novel symmetric monoadduct is consistent with derivatization at the [5,6] ring juncture on the Sc3N@C80 cage.     

Kinetic study on the alkaline hydrolysis of 1-aryl-2-phenyl-2-imidazolines. Basicity-rate of hydrolysis and structure relationships

Rate constants (k_obs) of hydrolysis in boiling alkaline ethanolic solution for six 1-aryl-2-phenyl-2-imidazolines were determined. The influence of substituents in the phenyl group at N-1 upon rate of hydrolysis was studied. When the imidazoline ring is considered to be a substituent of the benzene ring at N-1, a good correlation with the Hammett equation is found. It was observed that reaction rates were enhanced by electron-releasing phenyl substituents of N-1 and reduced by electron-withdrawing groups, providing a change in the mechanism of the reaction in the first case that was not observed in the second. Agreement with the Hammett equation allowed comparison between experimental and “calculated” rate constants which are nearly equal. An equation relating the rate constants with the ionization constants of imidazolinium ions is given.     

Photolysis of 1-alkylcycloalkanols in the presence of (diacetoxyiodo)benzene and I2. Intramolecular selectivity in the beta-scission reactions of the intermediate 1-alkylcycloalkoxyl radicals

The C-C beta-scission reactions of 1-alkylcycloalkoxyl radicals, generated photochemically by visible light irradiation of CH2Cl2 solutions containing the parent 1-alkylcycloalkanols, (diacetoxy)iodobenzene (DIB), and I2, have been investigated through the analysis of the reaction products. The 1-alkylcycloalkoxyl radicals undergo competition between ring opening and C-alkyl bond cleavage as a function of ring size and of the nature of the alkyl substituent. With the 1-propylcycloheptoxyl, 1-propylcyclooctoxyl,and 1-phenylcyclooctoxyl radicals, formation of products deriving from an intramolecular 1,5-hydrogen atom abstraction reaction from the cycloalkane ring has also been observed. The results are discussed in terms of release of ring strain associated to ring opening, stability of the alkyl radical formed by C-alkyl cleavage, and with cycloheptoxyl and cyclooctoxyl radicals, also in terms of the possibility of achieving a favorable geometry for intramolecular hydrogen atom abstraction.     

异硫氰酸与甲亚胺环加成反应机理的理论研究

对异硫氰酸与甲亚胺形成四元或六元环产物的环加成反应进行了理论研究,结果表明,一分子异硫氰酸与一分子甲亚胺形成四元环(1:1)产物P1的反应(1)为经过一个两性离子中间体的分步反应,其中第二步为速控步骤,其活化热垒为107.86kJ/mol.此外,反应(1)的中间体还可与另一甲亚胺或异硫氰酸分子继续反应形成两个不同的六元环(1:2或2:1)产物P2或P3;这两个反应均为协同反应,其活化势垒分别为15.88和21.82kJ/mol.这些结果与当异硫氰酸酯与亚胺发生环加成反应时,只有类似于P2和P3的两种六元环产物生成的实验事实一致。     

Benzindazoles based on triketones of the indan series

With phenylhydrazine, 2-acetonyl- and 2-phenacyl-2-phenylindan-1,3-diones form phenylhydrazones at the carbonyl group of the side chain. On prolonged heating, a reaction takes place with the expansion of the five-membered ring into a six-membered ring and the formation of the corresponding 5-hydroxy-1-phenylbenz[g]indazoles. A reaction mechanism is proposed. The structure of the compounds obtained has been confirmed by their IR and UV spectra.     

Kinetic study on the acid hydrolysis of 1-aryl-2-phenyl-2-imidazolines. Basicity-rate of hydrolysis and structure relationships

Rate constants (k_obs) of hydrolysis in sulfuric acid-water mixtures at 100° for five 1-aryl-2-phenyl-2-imidazolines were determined. The influence of substituents in the phenyl group at N-1 upon the rate of hydrolysis was studied. When the imidazoline ring is considered to be a substituent of the benzene ring at N-1, a good correlation with the Hammett equation is found. In opposition to the behavior in alkaline media it was observed that reaction rates were enhanced by electron-withdrawing phenyl substituents and reduced by electron-releasing groups providing, similarly, a change in the mechanism of the reaction in the second case that was not observed in the first. Agreement with the Hammett equation allowed comparison between experimental and “calculated” rate constants which are fairly close. An equation relating the rate constants with the pK_a values of the imidazolinium ions is given.     

Research on heterocyclic compounds. XX. Synthesis of trifluoromethyl derivatives of fused imidazole systems

A series of heterocyclic compounds having an imidazole ring fused with another ring with a bridgehead nitrogen atom and bearing a trifluoromethyl moiety was synthesized by reaction of 3-bromo-1,1,1-trifluoroacetone with various heteroarylamines. In some cases, an intermediate compound obtained together with the required product was isolated and its structure was elucidated: e.g., starting from 2-aminopyridine we have obtained 2-trifluoromethylimidazo[1,2-a]pyridine and 2-hydroxy-2-trifluoromethyl-2,3-dihydro-1H-imidazo [1,2-a]pyridinium bromide. Such results confirmed the mechanism previously proposed for this reaction.     

Reactions of azirines with sulfur nucleophiles. 2. Reactions of 2H-azirine with β,γ-dihydroxy thiols and β-dithiols. a new route to the synthesis of cyclic sulfides

The reaction of 2H-azirine with a number of dihydroxy thiols and dithiols leads to aziridin-2-yl alkyl sulfides. The latter readily isomerize to cyclic sulfides the size of the ring of which is determined by the length of the alkyl sulfide chain.For Communication 1, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 623–627, May, 1985.     

Research on unsaturated lactones. 49. Synthesis of thiazolidines that contain an α,β-unsaturated γ-lactone ring

The corresponding thiazolidines containing a lactone ring and their hydrochlorides and N-benzoyl derivatives were obtained by the reaction of 2-acetyl-3,4,4-trimethyl-2-buten-4-olide with thioglycolic or mercaptosuccinic acids and ammonium carbonate.See [1] for Communication 48.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 475–476, April, 1981.     

First and second generation total synthesis of the teicoplanin aglycon.

Full details of studies leading to the total synthesis of the teicoplanin aglycon are provided. Key elements of the first generation approach (26 steps from constituent amino acids, 1% overall) include the coupling of an EFG tripeptide precursor to the common vancomycin/teicoplanin ABCD ring system and sequential DE macrocyclization of the 16-membered ring with formation of the diaryl ether via a phenoxide nucleophilic aromatic substitution of an o-fluoronitroaromatic (80%, 3:1 atropisomer diastereoselection) followed by 14-membered FG ring closure by macrolactamization (66%). Subsequent studies have provided a second generation total synthesis which is shorter, more convergent, and highly diastereoselective (22 steps, 2% overall). This was accomplished by altering the order of ring closures such that FG macrolactamization (95%) preceded coupling of the EFG tripeptide to the ABCD ring system and subsequent DE ring closure. Notably, DE macrocyclization via diaryl ether formation on substrate 57, the key intermediate in the latter approach incorporating the intact FG ring system, occurred with exceptional diastereoselection for formation of the natural atropisomer (>10:1, 76%) without problematic C(2)(3) epimerization provided the basicity of the reaction is minimized.     

Theoretical study of the heptamethylbenzenium ion. Intramolecular isomerizations and C2, C3, C4 alkene elimination

Recent experimental work on the methanol-to-hydrocarbons (MTH) reaction in zeolite H-Beta suggests that the heptamethylbenzenium (heptaMB+) cation is an important intermediate. We have carried out quantum chemical calculations to investigate intramolecular isomerization reactions and eliminations of small alkenes such as ethene, propene, and isobutene from heptaMB+ isomers. Two types of reaction paths have been investigated for the alkene formation: One starting with an initial ring contraction, and one starting with an initial ring expansion of the heptaMB+ ion. The reaction starting with an initial ring contraction leads to a bicyclic species that may split off propene or, after further isomerizations, isobutene. Expansion to a seven-membered ring may, via further isomerizations, lead to formation of ethyl and isopropyl groups that may in turn be split off as ethene and propene. The calculations have been carried out at the B3LYP/cc-pVTZ//B3LYP/6-311G(d,p) level of theory with zero point energy corrections. Comparisons with experimental data are made where possible.     

1,5,2,4,6,8-Dithiatetrazocine. Synthesis, computation, crystallography and voltammetry of the parent heterocycle

The prototypal 1,5,2,4,6,8-dithiatetrazocine has been synthesized for the first time by two routes: reaction of 1,2,3,5-dithiadiazolium chloride with N,N,N'-tris(trimethylsilyl)formamidine in acetonitrile and reaction of 1,2,3,5-dithiadiazolyl radical with dioxygen in solution. Yields are low but single crystals could be obtained for an X-ray crystal structure determination which shows it to have the planar delocalized structure predicted by B3LYP/6-311+G(2d,p) hybrid DFT calculations. The crystal structure is strongly reminiscent of that of benzene in the same Pbca space group. Aromaticity is demonstrated by a (1)H NMR chemical shift of +9.70 ppm indicative of diamagnetic ring shielding and an intense low-energy optical absorption with λ(max) = 349 nm (MeOH). The voltammetric behaviour of the title compound is compared with that of 1,3λ(4)δ(2),5,2,4-trithiadiazepine; both resist electrochemical oxidation and reduction over a wide potential range as is typical for aromatic heterocycles.