Generation of an active acyl species from stable 1-methyl-2-acyl-1h-imidazoles

1-Methyl-2-(1′-cyano-1′-trimethylsilyloxy)alkyl-1H-imidazoles ($\text{2}$) were easily prepared from the corresponding stable carbonyl compounds, 1-methyl-2-acyl- ¹H-imidazoles ($\text{1}$). When the quarternary salts of $\text{2}$ were treated with various nucleophiles, reactive acyl species, which was presumed to be acylcyanide ($\text{12}$), was generated in situ under CC bond fission to result in producing the corresponding acylated compounds ($\text{5}$–$\text{10}$) in good yields.     

Cyclophane,XIV : darstellung polymethylierter [2.2]paracyclophane

Starting from 4, 5, 12, 13-tetrakis(methoxycarbonyl)[2.2]paracyclophane ($\text{1}$), the penta-($\text{4}$), hexa-($\text{6a}$–$\text{c}$), hepta-($\text{7}$), and octamethyl-($\text{8}$) derivatives have been prepared by a repetitive formylation-reduction sequence.     

Novel pyrimidine and its triazole fused derivatives: Synthesis and investigation of antioxidant and anti-inflammatory activity

In the present study, we have carried out the synthesis of novel dihydropyrimidinecarbonitrile (1a–c), its dimethylated adduct (2a–c), and hydrazine derivative (3a–c) of 2a–c and its triazole fused derivatives (4a–c, 5a–c and 6a–c). The structure of newly synthesized compounds was confirmed by IR, ¹H NMR, mass spectral data and elemental analysis. Further the novel derivatives were investigated for their in vitro antioxidant and anti-inflammatory activity. The results revealed that some of the tested compounds showed potent antioxidant and anti-inflammatory activity. The mass spectral pattern of 6a has been investigated in order to elucidate the structure.     

Transmission of electronic effects in certain ployenes

The effect of substituent variation in compounds of the general type R(CHCH)_nCHO (1) or p-RC₆H₄ (CHCH)_nCHO (2) on the stretching vibrations of the CHO group (ν_co), the dipole moments (μ), the long wave maxima (λ_max), and the halfwave potentials (E_{$\text{1}\text{2}$}) for the polarographic reduction of the CHO group have been studied as well as the influence of variation of substituent R on the rate constants (k) of the alkaline hydrolysis of polyenic esters R(CHCH)_nCOOEt (3). A linear relationship between the σ⁺, σ_c⁰ or σ_c⁺ values and the experimental values of ν_co, μ, gl_max, E_{$\text{1}\text{2}$} and k has been established, which indicates the importance of the mesomeric mechanism of the transmission of electronic effects through the chain of conjugated double bonds in compounds 1, 2 and 3. Transmission coefficients (π′) for one (π′_1F), two (π′_2F), three (π′_2F), and four (π′_4F) double bonds were calculated, and it was found that these values are bound together by the ratio: (π′_1F):(π′_2F):(π′_3F):(π′_4F) = (π′_1F):(π′_1F)²:(π′_1F)³:(π′_1F⁴, i.e. the influence of substituents R is decreased m a geometrical progression when the number of double bonds increases. The distribution of the electronic density in 1 was calculated by the LCAO SCF method in the Pariser-Parr-Pople approximation, and it was found that the π-electronic density values at the O atoms of the CHO group correlates well with σ_c⁰ constants and the calculated values of π′_1F, π′_2F, and π′_3F are bound together by the above ratio.     

Some observations relating to phosphorylation methods in oligonucleotide synthesis

A very convenient procedure for the conversion of ($\text{N}$),O-5′-protected deoxyribonucleosides ($\text{8}$) into the triethylammonium salts of the corresponding 3′-($\text{o}$-chlorophenyl) phosphates ($\text{9}$) is described. Good yields of partially-protected 3′→5′-dinucleoside phosphates ($\text{10}$) are obtained from the latter ($\text{9}$) and 3′-unprotected nucleoside building blocks ($\text{12a}$).     

Enamine chemistry—XXIII: The [4+2] cycloaddition reactions between enaminothiones and electrophilic olefins and acetylenes

The enamino-thione, 1c, reacts with acrylonitrile and 2-chloroacrylonitrile at room temperature to give 3,4-dihydro-4-(1-pyrrolidinyl)-2$\text{H}$-thiopyrans, 4 and 5, respectively. The reaction between 1-aryl-3-(1-pyrrolidinyl) (piperidino)-apropene-1-thiones, 1a-c (1d-f), and dimethyl acetylenedicarboxylate gives 4-(1-pyrrolidiny)(piperidino)-4$\text{H}$-thiopyrans, 6a-c (6d-f). Compounds 1a-c (1d-f) and ethyl propiolate produce 2-(1-pyrrolidinyl) (piperidino)-2$\text{H}$-thiopyrans, 8a-c (8d-f), and a new type of rearrangement is observed. The 2$\text{D}$-thiopyran, 9, is formed from 1b and ethyl 3$\text{D}$-propiolate, which elucidates the mechanism. ¹H and ¹³C NMR data of 6 and 7 are discussed.     

The synthesis of γ-fluoroisoleucine

Condensation of 3-fluoro-2-butanone ($\text{2}$) with alkyl diethylphosphonoacetates ($\text{4a–d}$) gave alkyl 4-fluoro-3-methyl-2-pentenoates ($\text{5a–d}$). Addition of bromine yielded alkyl-2,3-dibromo-4-fluoro-3-methylpentanoates ($\text{6a,b}$) which were dehydrobrominated to alkyl 2-bromo-4-fluoro-3-methyl-2- pentenoates ($\text{7a,b}$). Since these compounds could not be hydrogenated to the desired alkyl 2-bromo-4-fluoro-3-methylpentanoates ($\text{8a,b}$), another route was taken. The esters $\text{5a–d}$ were hydrogenated to alkyl 4-fluoro-3- methylpentanoates ($\text{11a–c}$) which were converted to their carbanions. Treatment with bromine gave esters $\text{8a–c}$, and iodine gave alkyl 4-fluoro-2-iodo- 3-methylpentanoates ($\text{12a,b}$). Esters $\text{8a–c}$ and $\text{12a,b}$ were converted to alkyl 2-azido-4-fluoro-3-methylpentanoates ($\text{13a–c}$) whose hydrogenation gave alkyl 2-amino-4-fluoro-3-methylpentanoates ($\text{14a–c}$). Hydrolysis afforded γ-fluoroisoleucine ($\text{1}$).     

3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

Facile syntheses of 2,4,6-cycloheptatrienyl ketones

The synthesis of the 2,4,6-cycloheptatrienyl ketones $\text{1a}$–$\text{1e}$ by two alternative routes is reported: Route 1): The adducts $\text{3a–c}$ from the phenyl(trimethylsiloxy)-acetonitriles $\text{2a–c}$, known as “umpolung” reagents, and tropylium tetrafluoroborate are cleaved by triethylammonium fluoride to form the aromatic cycloheptatrienyl ketones $\text{1a}$–$\text{1c}$. Route 2): the phenyl, methyl, and cyclopropyl ketone ($\text{1a}$, $\text{1d}$, $\text{1e}$) are prepared by treatment of the acid chloride $\text{7}$ with the corresponding organomanganese iodides RMnI ($\text{8a}$, $\text{8d}$, $\text{8e}$). The Fe-catalyzed coupling reaction of the acid chloride $\text{7}$ with a Grignard reagent was also used for the preparation of ketone $\text{1b}$.     

The reaction of 2-azaallenium salts with carbodiimides and tert-butyl isocyanide

2-Azaallenium salts $\text{1}$ react with diisopropyl carbodiimide to afford the formal dihydro-1,3-diazetium salts $\text{5}$. The structure of $\text{5c}$ has been confirmed by an X-ray diffraction analysis. With the carbodiimide $\text{2e}$ the tetraphenyl-2-azaallenium salt $\text{1a}$ reacts to give the guanidinium compound $\text{6}$.The diazetium salts $\text{5}$ react with further carbodiimide to afford the formal 2-azaallenium salts $\text{11}$. With tert-butyl isocyanide the 2-azaallenium salts $\text{1}$ undergo an Ugi reaction to yield the nitriles $\text{14}$.     

Preparation and reactivity of mesoionic 1,2,4-triazolo-[4,3-b]-1,2,4-triazole derivatives

A number of mesoionic compounds (2) derivatives of the 1,2,4-triazolo[4,3-$\text{b}$]-1,2,4-triazole ring system have been prepared from 4-amino-1 -methyl -3,5-bis(methylthio)- 1,2,4-triazolium cation and aryl isothiocyanates. Compounds ((2) react with methyl iodide to give the methiodides ((3) which undergo ring opening to the monocyclic compounds ((4) through sulfur extrusion under thermal conditions. Methiodides ((3) by sequential treatment with malononitriIe and hydrochloric acid lead to the pyrazolo[5,1-$\text{c}$]-1,2,4-triazole (6).     

Electronic control of stereoselectivity-21 : Stereochemical parallelism between dienophilic capture and singlet oxygenation of isodicyclopentadiene derivatives

The stereochemistry and product distribution resulting from reaction of 4',5',6',7'- tetrahydrospirol[cyclopropane-1,2']-[4,7]methano[2$\text{H}$]indene(5), endo-2-methyl(6a) and 2,2-dunethyl-4,7-dihydro-4,7-methano-2$\text{H}$-indene (6b), as well as 4',5',6',7'-tetrahydrospiro[cyclopentane-1,2']-[4,7]methano-[2$\text{H}$]indene (7) with singlet oxygen have been determined. Stereochemical assignments to the diepoxide products were readily deduced by ¹³C-NMR comparison with the spectra of the parent isomcrs of established structure (X-ray). To unravel the stereochemistry of the epoxy aldehydes, recourse was made to 2D NOE experiments The observed stereosclectivity and reaction profile of each substrate are analyzed and placed in proper mechanistic and energetic perspective.     

Biosynthetic pathway of iridoid glucosides in Gardenia jasminoides f. grandiflora cell suspension cultures after iridodial cation formation

Administration of ²H- or ¹³C-labeled monoterpenes to $\text{Gardenia}$$\text{jasminoides}$ f. $\text{grandiflora}$ cell suspension cultures demonstrated that iridoid glucosides of the suspension cultures are biosynthesized, after iridodial cation formation from 10-oxocitral (3), via 8-epiiridodial (13), 8-epiiridotrial (14), boschnaloside (8-epiiridotrial glucoside) (12) and dehydroiridotrial glucoside (8). In addition, the coexistence of a route via iridodial cation (4), dehydroiridodial (6), dehydroiridotrial (15) and dehydroiridotrial glucoside (8) is conceivable.     

Benzannelated annulenes -12. : Theoretical study of geometries and 1H chemical shifts of benzannelated [14] annulenes

The geometries and the ¹H chemical shifts of dihydropyrene $\text{1}$ and its benzannelated derivatives $\text{2}$–$\text{8}$ have been studied by means of semiempirical quantum chemical procedures. The calculated bond lengths of $\text{1}$ and proton shifts of $\text{1}$ – $\text{5}$ are in good accord with the corresponding experimental values. We show that monobenzannelation in $\text{2}$ – $\text{4}$ causes considerable bond length alternation in the [14] perimeter and hence reduced diatropocity. The same is true for the phenanth-fused dibenzannelated compounds $\text{4}$ and $\text{7}$. On the other hand we report evidence that anth-fused dibenzannelated dihydropyrenes $\text{5}$, $\text{6}$, and $\text{8}$ should be characterized by symmetric geometrical structures without significant bond length alternation thus leading to enhanced diatropicity.     

1,1-Diaminosubstituted 2-azaallenium salts: preparation and barriers to topomerization

Dialkylcarbodiimides, $\text{5}$, react with iminium salts, $\text{6}$, to afford the formal 1,1-diaminosubstituted 2-azaallenium salts $\text{3}$. According to dynamic NMR measurements compounds $\text{3}$ must be regarded as alkylidene-guanidinium salts $\text{A}$, undergoing a fast topomerization via a transition state $\text{B}$ with allene geometry (2G⁼₂₆₅ = 45.9 ± 1 kJmol^-1 for $\text{3f}$) and a slower rotation around the peripheral C-N bonds (transition state $\text{C}$; 2G⁼₂₉₀⁼ 58.0 ± 1 kJmol^-1 for $\text{3f}$).     

Electronic spectra of 12-S-CIS conformationally locked retinals

The electronic absorption spectra of the four new 12-$\text{s}$-$\text{cis}$-locked retinals (1a–1d) bearing 7-$\text{trans}$, 11-$\text{trans}$ double bond geometries are described and compared with those of analogous 7-$\text{trans}$, 11-$\text{cis}$-geometries (1e–1h) and parent retinals (2a-h).     

Conformation and barrier to inversion of a 12-membered heterocycle containing two disulfide bonds

Raman and ¹H NMR spectroscopic data obtained for a dimeric product 4c formed on iodine oxidation of N-pnenyl-N-thiomethyl-thioglycolic acid amide (3c) indicate that this product is 4,11-diphenyl-4,11-diaza-1,2,7,8-tetrathia-cyclododecane-5,10-dione. The barrier to interconversion between the conformers of 4c has been determined by DNMR. The height of the barrier (ΔG^≠ = 17.3 ±0.1 $\text{kcal}\text{mol}$) is in agreement with the proposed structure. This investigation thus gives a support to the previously proposed mechanism of regiospecific dimeric oxidations of unsymmetrical dithols of type 3c.     

Synthesis and 13C nmr characterization of some π-excessive heteropolyaromatic compounds

Several π-excessive heteropolyaromatic compounds, which contain furan and thiophen ring and are possible antifungal agents, have been synthesized in good yields according to two general methods. The first method has been used to prepare compounds possessing thiophens linked by their 2- and 5-positions, such as the ter-aryls $\text{2b}$, $\text{2d}$ and $\text{2a}$. Two precursors of these compounds have been obtained either by the Glaser reaction, or using a novel Pd-mediated reaction. The second method,which consists of the Ni-or Pd-catalyzed heteroarylation of heteroarene halides via cross-coupling with heteroaryl Grignard reagents or zinc halides,has been used to prepare the bi-aryls $\text{1a-e}$, which contain two heteroaromatic units, and the ter-aryl $\text{2c}$. Compound $\text{1e}$ has been also prepared starting from 2-(2-thienyl) furan ($\text{1c}$) by selective lithiation, followed by bromination.The ¹³C NMR signals of $\text{1a-e}$ and $\text{2a-d}$ have been assigned on the basis of the literature data and by relaxation measurements. Relaxation data have been also used to obtain qualitative informations on the conformational equilibria of the bi-aryls $\text{1a}$, $\text{1c}$ and the ter-aryls $\text{2a-d}$.