Ethynyl Derivatives Research Articles

Cycloaddition reactions of ICNO

The mechanism and selectivity of cycloaddition reactions of iodonitrile oxide, ICNO, have been studied with theoretical methods for the first time using MR-AQCC coupled-cluster and B3LYP DFT methods. Calculations have predicted that the favoured ICNO dimerisation process is a multi-step reaction to diiodofuroxan involving dinitrosoethylene-like intermediates. The ICNO cycloaddition with nitriles and ethynyl derivatives is a synchronous process favouring the formation of 1,2,4-oxadiazole and 1,2-oxazole derivatives, respectively. The cycloaddition reactions of ICNO have been studied experimentally by generating ICNO from AgCNO and iodine. Diiodofuroxan is obtained, however, even at the presence of nitriles.

An Improved Synthesis of (4-{4-Hydroxy-3-isopropyl-5-[(4-nitrophenyl)ethynyl]benzyl}-3,5-dimethylphenoxy)acetic Acid (NH-3)

Sonogashira coupling of methyl {4-[3-iodo-5-isopropyl-4-(methoxymethoxy)benzyl]-3,5-dimethylphenoxy}acetate with (trimethylsilyl)acetylene afforded the corresponding (trimethylsilyl)ethynyl derivative in quantitative yield. Copper-free palladium-catalyzed coupling of this intermediate with 1-iodo-4-nitrobenzene afforded methyl (4-{3-isopropyl-4-(methoxymethoxy)-5-[(4-nitro-phenyl)ethynyl]benzyl}-3,5-dimethylphenoxy)acetate in high yield. Saponification of the ester group, followed by the removal of the methoxymethyl group afforded (4-{4-hydroxy-3-isopropyl-5-[(4-nitrophenyl)ethynyl]benzyl}-3,5-dimethylphenoxy)acetic acid (NH-3).

α,β‐Unsaturated and Saturated Derivatives of Be, Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

The gas-phase acidity of R--XH (R=H, CH(3), CH(2)CH(3), CH==CH(2), C[triple chemical bond]CH; X=Be, Mg, Ca) alkaline-earth-metal derivatives has been investigated through the use of high-level CCSD(T) calculations by using a 6-311+G(3df,2p) basis set. BeH(2) is a stronger acid than BH(3) and CH(4) for two concomitant reasons: 1) the dissociation energy of the Be--H bond is smaller than the dissociation energies of the B--H and C--H bonds, and 2) the electron affinity of BeH(.) is larger in absolute value than those of BH(2) (.) and CH(3) (.). The acidity also increases on going from BeH(2) to MgH(2) due to these two same factors. Quite importantly, despite the fact that the X--H bonds in the R--XH (X=Mg, Ca) derivatives exhibit the expected X(delta+)--H(delta-) polarity, they behave as metal acids in the gas phase and only Be derivatives behave as carbon acids in the gas phase. The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deprotonation of the system is accompanied by a cyclization that stabilizes the anion. Similarly to that found for derivatives that contain heteroatoms from groups 14, 15, and 16, the unsaturated compounds are stronger acids than the saturated counterparts, with the only exception of the Ca-vinyl derivative. Most importantly, among ethyl, vinyl, and ethynyl derivatives containing a heteroatom of the main group of the Periodic Table, those containing Be, Mg, and Ca are among the strongest gas-phase acids.

Radioiodinated ligands for the estrogen receptor: Effect of different 7-cyanoalkyl chains on the binding affinity of novel iodovinyl-6-dehydroestradiols

Three novel 17 α-ethynyl- Δ 6,7-estra-3,17 β-diols and their 17 α-[ 125I]-iodovinyl derivatives, containing different C7-cyanoalkyl chains, were studied as potential radioligands for the estrogen receptor. The influence of the chain length on the biological behaviour of the compounds was assessed through in vitro ER binding assays of the ethynyl derivatives and breast cancer cell uptake studies of the 17 α-[ 125I]-iodovinyl- Δ 6,7-estra-3,17 β-diols. A difference in alkyl chain induced a decrease in ER binding affinities of substances, however, the receptor-binding affinities (RBA) of all compounds were lower than that of estradiol itself. In addition, a non-specific cell binding was observed which is in accordance with the encountered ethynyl RBA values suggesting that the uptake is not ER mediated.

Synthesis and Anti-HIV Activity of 4′-Substituted 4′-Thiothymidines: A New Entry Based on Nucleophilic Substitution of the 4′-Acetoxy Group

Diacetoxylation of 1-(2,5-dideoxy-beta-L-glycero-pent-4-eno-4-thiofuranosyl)thymine (13) with Pb(OAc) 4 allowed introduction of an acetoxy leaving group to the 4'-position. Nucleophilic substitution of the resulting 4'-acetoxy derivative (14) with silicon reagents enabled us to prepare the 4'-phenylthio (17a), 4'-azido (18a), 4'-methoxy (20a), and 4'-allyl (21a) analogues of 4'-thiothymidine. 4'-Cyano ( 25a) and 4'-ethynyl (31) nucleosides were also synthesized from 3',5'-bis-O-TBDMS derivative (24). Among novel 4'-substituted 4'-thiothymidines, the 4'-azido (33), 4'-cyano (36), and 4'-ethynyl (37) derivatives were found to show potent inhibitory activity against HIV-1 and HIV-2. It is noteworthy that 36 and 37 were also inhibitory against replication of HIV variant resistant to 3TC (HIV-1 M184V), being as potent as against HIV-1 IIIB.

The Boat Conformation in Pyrazaboles. A Theoretical and Experimental Study

Experimental data are combined with theoretical calculations to study the stability of the boat conformation of the pyrazabole ring. For the experimental studies, new BH2- and BF2-pyrazaboles disubstituted with iodo or ethynyl groups at the 2- and 6-positions have been prepared and structurally characterized. We have found different molecular structures and crystal packings depending on the substituents. The iodo derivatives have a bent molecular shape due to the boat conformation of the pyrazabole ring, and the molecules are arranged in stacks with the same conformation (all-up or all-down boat conformation) along the crystallographic b axis. Stacks of molecules with the same conformation interact in a plane by means of iodo−iodo short contacts. However, the ethynyl derivatives are formed by bent-shaped molecules for BH2 and planar structures for BF2. Density functional theory and ab initio calculations have been performed on these compounds and on unsubstituted analogues to understand the effect of subs...

Subphthalocyanine−Dehydro[18]annulenes

A subphthalocyanine trimer built around a dehydro[18]annulene core was prepared. The synthesis was achieved through direct homocoupling of an ortho-diethynyl-functionalized subphthalocyanine, obtained by palladium-catalyzed cross-coupling of the corresponding diiodo-subphthalocyanine with an ethynyl derivative. The lower analogue dehydro[12]annulene did not form in these homocoupling conditions. The trimers were fully characterized and their electrochemical properties investigated.

An Alternative Synthetic Method for 4′-C-Ethynylstavudine by Means of Nucleophilic Substitution of 4′-Benzoyloxythymine Nucleoside

For the synthesis of 2′,3′ -didehydro-3′ -deoxy-4′ -C-ethynylthymidine (8: 4′ -Ed4T), a recently reported promising anti-HIV agent, a new approach was developed. Since treatment of 1-(2,5-dideoxy-β-l-glycero-pent-4-enofuranosyl)thymine with Pb(OBz)4 allowed the introduction of a 4′-benzoyloxy leaving group, nucleophilic substitution at the 4′ -position became feasible for the first time. Thus, reaction between the 4′-benzoyloxy derivative (11) and Me3SiC ≡ CAl(Et)Cl as a nucleophile led to the isolation of the desired 4′-“down”-ethynyl derivative (15) stereoselectively in 62% yield.

Synthesis of (±)-9-[ c-4, t-5-bis(hydroxymethyl)cyclopent-2-en- r-1-yl]-9 H-adenine (BCA) derivatives branched at the 4′-position based on intramolecular S H2′ cyclization

Synthesis of 4′-branched BCA analogues ( 5) was carried out. Stereospecific construction of the cis-disposed 4′-carbon-substituents and 5′-hydroxymethyl group was secured by employing the bicyclo[3.3.0]lactone 16 as a key intermediate, which was prepared by radical-mediated intramolecular S H2′ cyclization of the phenylselenomethyl ester 15. After manipulation of the double bond of 16, bis(Boc)adenine was introduced based on the Mitsunobu reaction of the allyl alcohol 24. Transformation of the lactone function of 27 allowed preparation of the 4′-hydroxymethyl ( 31), the 4′-vinyl ( 32), the 4′-cyano ( 34), and the 4′-ethynyl ( 35) derivatives. Anti-HIV and anti-HCV activities of the free nucleosides 36– 38 were also examined.

Pt×××Pt and π-π* Interactions in Luminescentσ-Alkynyl Platinum(II) Terpyridine Complexes

The authors report the formation of gels and liquid crystals induced by Pt×××Pt and π-π* interactions. Syntheses of the pivotal ethynyl platforms are based on gallate-substituted derivatives with methyl, dodecyl (C12H25) or phytol-like (C20H41) substituents. The final complexes were prepared by a cross-coupling reaction under anaerobic conditions between the terminal ethynyl derivatives and [(terpy)PtCl]BF4 (terpy = 2,2′:6′,6-terpyridine). The reaction is catalyzed by CuI (ca. 6 mol%), and triethylamine is required to quench the nascent HCl. Compound 2b was found to be a good gelator of dodecane. Dark-green gels displaying a thermally reversible sol-gel-phase transition were obtained from hot dodecane solutions. The Pt×××Pt interactions were identified based on unique absorption and emission features and further confirmed by X-ray data of the columnar liquid crystal.

Excited States and Two-Photon Absorption of Some Novel Thiophenyl Pt(II)−Ethynyl Derivatives

The photophysical characterization of two new compounds related to bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine)platinum(II), here abbreviated Pt1, is reported. For the first new compound ATP1, the inner phenyl rings (closer to the Pt atom) in Pt1 are replaced by thiophene rings bridging at the 2,5-positions. In compound ATP2, the outer phenyl groups are replaced by thiophene rings bonded at the 2-position. Specifically, we report on the fluorescence quantum yield, two-photon absorption, triplet decay times and two-photon absorption induced emission spectra of the molecules in THF solutions. The results were compared with those of Pt1 and Pt1 capped with an acetonide-protected 2,2-bis(methylol)propionic acid (bis-MPA) ester group (Pt1-G1). The photophysical properties of the organic dye 7-(diethylamino)coumarin (Coumarin 110) were determined and used as a reference material. The two-photon absorption cross section around 720-740 nm of ATP1 and ATP2 was found to be of the same order of magnitude as for Pt1-G1, i.e., between 5 and 10 GM, but slightly larger for ATP1 than for ATP2 (1 GM = 1 Göppert-Mayer = 10(-50) (cm(4) s)/photon). The fluorescence decay time of all compounds was found to be very short (subnanosecond) with quantum yields 0.0045, 0.0007, 0.0011 and 0.0020 for ATP1, ATP2, Pt1-G1 and Pt1, respectively, measured at excitation wavelength 373 nm. Just as Pt1 and Pt1-G1, both thiophenyl derivatives showed large intersystem crossing capabilities and phosphorescence, characteristic for a triplet state that can enhance the nonlinear absorption and optical power limiting by triplet state absorption. The phosphorescence emission of the thiophenyl derivatives was red-shifted in comparison with Pt1 and Pt1-G1, and the phosphorescence decay times were on the order of 200-500 ns, as for the Pt1 compound.

Heterometallic complexes containing 1,1′-(C [tbnd]C) 2Fc′ units linking two different metal centres

Proto-desilylation of 1-(Me 3SiC C)-1′-{Cp ∗(dppe)RuC C}Fc′ ( 1) afforded the corresponding ethynyl derivative 2, from which the green Co 2(μ-dppm) n (CO) 8−2 n ( n = 0, 1) adducts 3 and 4 were obtained. Replacement of the ethynyl proton in reactions between 2 and AuCl(PPh 3), Hg(OAc) 2 or FeCl(dppe)Cp ∗ gave complexes 1-(RC C)-1′-{Cp ∗(dppe)RuC C}Fc′ [R = Au(PPh 3) 5, 1/2Hg 6, Fe(dppe)Cp ∗ 8]; the latter gave bis-vinylidene 9 with MeI, characterised (as was 2) by a single crystal X-ray study. Oxidative coupling of 2 (CuCl/tmeda/acetone, air) gave diyne 10, while coupling of 5 with Co 3(μ 3-CBr)(μ-dppm)(CO) 7 afforded 1-{Cp ∗(dppe)RuC C}-1′-{(OC) 7(μ-dppm)Co 3(μ 3-CC C)}Fc′ ( 11). Cyclic voltammetric measurements indicated that there was no significant electronic coupling between the end-groups through the ferrocene centre in any of these compounds.

Nucleophilic Substitution at the 4‘-Position of Nucleosides: New Access to a Promising Anti-HIV Agent 2‘,3‘-Didehydro-3‘-deoxy-4‘-ethynylthymidine

For the synthesis of 2',3'-didehydro-3'-deoxy-4'-ethynylthymidine (8: 4'-Ed4T), a recently reported promising anti-HIV agent, a new approach was developed. Since treatment of 1-(2,5-dideoxy-beta-L-glycero-pent-4-enofuranosyl)thymine with Pb(OBz)4 allowed the introduction of the 4'-benzoyloxy leaving group, nucleophilic substitution at the 4'-position became feasible for the first time. Thus, reaction between the 4'-benzoyloxy derivative (14) and Me3SiCCAl(Et)Cl as a nucleophile led to the isolation of the desired 4'-"down"-ethynyl derivative (18) stereoselectively in 62% yield. As an application of this approach, other 4'-substituted nucleosides, such as the 4'-allyl (24a) and 4'-cyano (26a) derivatives, were synthesized using organosilicon reagents. In these instances, pretreatment of 14 with MeAlCl2 was necessary.

Camouflaged Carborarods Derived fromB-Permethyl-1,12-diethynyl-para- andB-Octamethyl-1,7-diethylnyl-meta-carborane Modules

Rigid camouflaged carborarods constructed from the corresponding C,C'-diethynyl derivatives of B-decamethyl-1,12-dicarbadodecaborane(12) (6) and B-octamethyl-1,7-dicarbadodecaborane(12) (48) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p-carborane and m-carborane cages are linked through their carbon vertices by using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid-rod molecules. The oxidative coupling of bis(ethynyl) derivatives of 6 generates oligomers containing, on average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex para-carborane cages in a series of model C,C'-diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage C--C bond lengths with cage size was observed and was attributed to hybridization effects. B-Permethylation had no significant structural effect with either 10- or 12-vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B-permethylated derivatives were increased through the operation of a steric "bumper-car" process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina-carborarods using ethynyl derivatives of 6 as precursors is described.

Diosmium(III) Compounds Supported by 2-Anilinopyridinate and Novel Alkynyl Derivatives

The reaction between Os(2)(OAc)(4)Cl(2) and Hap (Hap is 2-anilinopyridine) under prolonged refluxing conditions resulted in an Os(III)(2) compound, Os(2)(ap)(4)Cl(2) (1), that can be crystallized as either the cis-(2,2) isomer from a CH(3)OH-CH(2)Cl(2) solution or the (3,1) isomer from a hexanes-CH(2)Cl(2) solution. Compound 1 undergoes facile reactions with LiC(2)Y to yield a series of Os(2)(ap)(4)(C(2)Y)(2) compounds with Y as Ph (2), ferrocenyl (3), SiMe(3) (4), and C(2)SiMe(3) (5). X-ray diffraction study of compound 2 reveals solvent-dependent isomerism similar to that of the parent compound 1. Compound 1 has Os-Os distances of 2.3937(8) and 2.3913(8) Angstroms for the cis-(2,2) and (3,1) isomers, respectively, and is paramagnetic (S = 1). Both the ethynyl derivatives 2-4 and butadiynyl derivative 5 are diamagnetic and have Os-Os distances of 2.456(1), 2.471(1), and 2.481(1) Angstroms for the cis-(2,2) and (3,1) isomers of 2 and (3,1) isomer of 4, respectively. Compounds 1-5 exhibit multiple one-electron redox couples in their cyclic voltammograms, including a reversible Os(2)(8+/7+) couple for 2. Resonance Raman spectra of both compounds 1 and 2 are reported.

Acidity Trends in α,β‐Unsaturated Sulfur, Selenium, and Tellurium Derivatives: Comparison with C‐, Si‐, Ge‐, Sn‐, N‐, P‐, As‐, and Sb‐Containing Analogues

The gas-phase acidity of CH3-CH2XH (X=S, Se, Te), CH2=CHXH (X=S, Se, Te) and PhXH (X=S, Se) compounds was measured by means of Fourier transform ion cyclotron resonance mass spectrometry. To analyze the role that unsaturation plays on the intrinsic acidity of these systems, a parallel theoretical study, in the framework of the G2 and the G2(MP2) theories, was carried out for all ethyl, ethenyl (vinyl), ethynyl, and phenyl O-, S-, Se-, and Te-containing derivatives. Unsaturated compounds are stronger acids than their saturated analogues, because of the strong pi-electron donor ability of the heteroatoms that contributes to a large stabilization of the unsaturated anions. Ethynyl derivatives are stronger acids than vinyl compounds, while phenyl derivatives have an intrinsic acidity intermediate between that of the corresponding vinyl and ethynyl analogues. The CH2=CHXH vinyl compounds (enol-like) behave systematically as slightly stronger acids than their CH3-C(H)X (keto-like) tautomers. Vinyl derivatives are stronger acids than ethyl compounds, because the anion stabilization attributable to unsaturation is greater than that undergone in the neutral compounds. Conversely, the enhanced acidity of the ethynyl derivatives with respect to the vinyl compounds is due to two concomitant effects, the stabilization of the anion and the destabilization of the neutral compound. The acidities of ethyl, vinyl, and ethynyl derivatives containing heteroatoms of Groups 14, 15, and 16 of the periodic table are closely related, and reflect the differences in electronegativity of the CH3CH2-, CH2=CH-, and CH[triple chemical bond]C- groups.

Hydrosilylation of cyclohexene, 1-methylcyclohexene, and isopropylidenecyclohexane

Hydrosilylation of cyclohexene and isopropylidenecyclohexane with chloro(methyl)silanes Me3−nSiHCln (n = 1–3) gives rise to cyclohexyl- and chloro(2-cyclohexylpropyl)methylsilanes. Hydrosilylation of 1-methylcyclohexene with chlorodimethylsilane (n = 1) occurs anomalously and involves double-bond migration to form a mixture of seven compounds: the cis and trans isomers of 2-, 3-, 4-chlorodimethyl(methylcyclohexyl)silanes and chlorodimethyl(cyclohexylmethyl)silane. Chlorodimethylsilane (n = 2) adds to 1-methylcyclohexene to form a mixture of the cis and trans isomers of dichloro(methyl)(2-methylcyclohexyl)silane and dichloro(cyclohexylmethyl)methylsilane. With trichlorosilane (n = 3), no other products than trichloro(cyclohexylmethyl)silane are formed. The hydrosilylation products were reacted with ethynylmagnesium bromide to synthesize the corresponding ethynyl derivatives.

Molecular Structures of Acetylene Derivatives of Tin. VIII Trimethylstannylacetylene: Use of Results of Quantum-Chemical Calculations and Spectroscopic Measurements in Analysis of Gas-Phase Electron Diffraction Data

Structural analysis of electron diffraction data on trimethylstannylacetylene, (CH3)3SnC≡CH (1), obtained in the previous investigation (the nozzle temperature being 22°C), has been performed with consideration of nonlinear kinematic effects at the first-order level of perturbation theory (h1). The geometry and force field of 1 have been calculated by the RHF and MP2 (“frozen core”) methods. The effective core potential in SBK form and the optimized 31G* valence basis set have been applied in the case of Sn atom. The 6-311G** basis set have been used for carbon and hydrogen atoms. Vibrational spectra of the light and two deuterated isotopomers of 1 have been interpreted using the C 3v equilibrium molecular symmetry. For this purpose, the procedure of scaling the quantum-chemical force field by fitting the calculated frequencies to the experimental ones has been employed. The root-mean-square (RMS) vibrational amplitudes and shrinkage corrections used in the electron diffraction analysis have been calculated from the scaled quantum-chemical force field. It has been shown that flexibility of the linear fragment in 1 decreases considerably compared to that of the symmetrically substituted acetylene fragment in the (CH3)3SnC≡CSn(CH3)3 molecule (2). Using these data, we refined the geometrical parameters of 1 in terms of a static C 3v symmetry molecular model. The following r h1 values have been obtained (the bond distances are given in A and the valence angles in degrees): Sn—CMe 2.147(7), Sn—C≡2.096(17), C≡C 1.237(11), CMe—H (av.) 1.091(4), CMe—Sn-C≡107.1(7), Sn—CMe—H (av.) 113.4(6). The values in parentheses are experimental total errors including least-squares standard deviation values and scale uncertainties. The structural parameters of linear fragments in both ethynyl derivatives of Sn 1 and 2 are found to be virtually equal.

Functional dyes: bipyridines and bipyrimidine based boradiazaindacene

The synthesis of molecules bearing pyridine, 2,2 ′-bipyridine or 2,2 ′-bipyrimidine donor units appended with one or two highly luminescent indacene fragments was undertaken by using two distinct pathways. The first used direct condensation of krytopyrrole with the corresponding aldehydes. The second, and more universal is based on a Pd cross-coupling reaction between an iodo functionalized BODIPY and the corresponding stable ethynyl derivatives. All compounds are strongly luminescent in solution with quantum yields as high as 70%. Interlocking of two 6,6 ′-BODIPY substituted bipyridines around a single copper(I) center is observed by proton NMR and cyclic voltammetry. These synthetic routes have made a variety of functionalized dyes available for studies of their optical properties in the presence of incoming cations, of their coordination chemistry and as light emitting solid state materials.

Supramolecular equivalence of ethynyl, chloro, bromo and iodo groups. A comparison of the crystal structures of some 4-phenoxyanilines

4-(4′-Iodo)phenoxyaniline is isostructural to the corresponding bromo, chloro and ethynyl derivatives in contrast to 4-iodoaniline which is not isostructural to its bromo, chloro and ethynyl counterparts. This difference is rationalised in terms of conditional isomorphism.