1529-40-4Relevant academic research and scientific papers
Photochemical generation of 9-Fluorenyl radicals
Duffy, Ian R.,Leigh, William J.,Afifi, Hanan,Ebead, Abdelaziz,Fournier, René,Lee-Ruff, Edward
, (2019)
A series of 9H-fluorenols and 9H, 9′H-bifluorenyls were irradiated in less polar solvents giving photoproducts derived from their corresponding 9H-fluorenyl radicals. These transient species were directly observed by laser flash photolysis and their UV/visible spectra compared with those of their corresponding cations. Theoretical calculations (density functional theory [DFT]) of these intermediates indicate their destabilizing nature in similar fashion to the antiaromatic character of the corresponding cations.
Proton transfer from carbon acids to carbanions. 1. Reactions of various carbon acids with the anions of substituted benzylmalononitriles in 90% Me2SO-10% water. determination of intrinsic barriers of identity reactions from the marcus relationship
Bernasconi, Claude F.,Ni, Jiu Xiang
, p. 5060 - 5066 (1993)
A kinetic study of the reversible deprotonation of 9-cyanofluorene (2), 1,3-indandione (3), 4-nitrophenyl-acetonitrile (4), (3-nitrophenyl)nitromethane (5), and (4-nitrophenyl)nitromethane (6) by the anions of substituted benzylmalononitrile (1-X-) in 90% Me2SO-10% water (v/v) at 20 °C is reported. Intrinsic rate constants and intrinsic barriers of these reactions have been determined by extrapolation or interpolation of Br?nsted plots whose slopes (β) are all close to 0.5. Intrinsic barriers of the identity reactions CH + C- ? C- + CH (CH = 2,3,4,and phenylnitromethane) have been estimated on the basis of the Marcus equation, coupled with either a plausible value for the identity barrier of the reaction AH+ + A ? A + AH+ (A = piperidine or morpholine) ("amine method") or a plausible value for the identity barrier of the reaction 2 + 2- ? 2- + 2 ("9-cyanofluorene method"). There are discrepancies in the identity barriers for CH + C- ? C- + CH (CH = 2, 3, 4, and phenylnitromethane) calculated by the two methods. Possible reasons for these discrepancies and the significance of the results in terms of the validity and scope of the Marcus equation are discussed.
Photochemical generation of 9h-fluorenyl radicals
Dyblenko, Tatiana,Chtchemelinine, Andrei,Reiter, Ryan,Chowdhury, Ruhul Q.,Enaya, Alexander,Afifi, Hanan,Fournier, Rene,Mladenova, Gabriela,Lever, Alfred Barry P.,Lee-Ruff, Edward
, p. 470 - 475 (2014)
A series of 9-substituted fluorenols and 9,9′-disubstituted-9, 9′-bifluorenyls were irradiated to give products derived from fluorenyl radicals. Product distribution was solvent dependent. A TEMPO adduct was isolated from the photoexcitation of 9-fluorenol. An unusual unsymmetrical 3,9′-bifluorenyl was observed from the photolysis of 9- trifluoromethylfluorenol and 9,9′-di(trifluoromethyl)-9,9′- bifluorenyl in more polar or hydrogen-bonding solvents. The electronic nature of 9-substituted fluorenyl radicals was probed using theoretical calculations showing the dipolar character of species with electron-deficient groups. These constitute the first examples of "doubly destabilized" radicals. Substituted 9-fluorenols and 9,9′-bifluorenyls undergo photolysis to give products derived from 9-fluorenyl radicals. These intermediates decay by hydrogen abstraction giving 9H-fluorenes, or coupling to 9,9′bifluorenyls. The 9-trifluoromethyl-9-fluorenyl radical undergoes an unusual coupling to the unsymmetrical 9,3′-bifluorenyl.
Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
An, Feng,Maji, Biplab,Min, Elizabeth,Ofial, Armin R.,Mayr, Herbert
supporting information, p. 1526 - 1547 (2020/02/04)
The Br?nsted basicities pKaH (i.e., pKa of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 aH aH aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pKaH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log?k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, -, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Br?nsted basicities.
Synthesis and structure-activity relationships of A novel class of dithiocarbamic acid esters as anticancer agent
Hou, Xueling,Ge, Zemei,Wang, Tingmin,Guo, Wei,Wu, Jun,Cui, Jingrong,Lai, Chingsan,Li, Runtao
experimental part, p. 320 - 332 (2011/11/05)
Based on a novel lead compound 4-methylpiperazine-1-carbodithioic acid 3-cyano-3,3-diphenylpropyl ester 1, the systematic structural modification was carried out. All the synthesized compounds were evaluated for their in-vitro anticancer activities on four to six different cell lines at three different concentrations. Most of the tested compounds could selectively inhibit the growth of HL-60 and Bel-7402 cell lines at a medium concentration. Four compounds (3f, 3g, 3n, and 5) were selected for the IC50 test, and the results revealed that three compounds (3g, 3n, and 5) showed almost the same or a slightly weaker activity than compound 1 against HL-60, and three compounds (3f, 3g, and 3n) showed >2-fold higher potency than compound 1 against Bel-7402. The in-vivo efficacy of 3n · HCl was evaluated with transplanted hepatocyte carcinoma 22 as an in-vivo test model. It was found that 3n · HCl could inhibit significantly the growth of tumor, and that this effect was dose-dependent. Meanwhile, the compound 3n · HCl showed low toxicity compared with compound 1 · HCl as evidenced by the little body-weight loss. These results confirmed that compound 3n · HCl is more potent than the lead compound 1 · HCl. Preliminary structure-activity relationships indicated that: a) Both nitrile group and the cyclic amine containing at least two nitrogens were indispensable moieties to keep the activity; b) substitution of the piperazine ring is unfavorable for the improvement of activity; c) the suitable linker joining the piperazinyl dithiocarboxyl and diphenylacetonitril group should be ethylene; d) a non-coplanar arrangement of the two benzene rings appears to be essential for activity. Based on a novel lead compound 4-methyl-piperazine-1-carbodithioic acid 3-cyano-3,3-diphenyl-propyl ester 1, the systematic structural modification was carried out. Compounds 3g and 3n were found to show more potent biological activities than lead compound 1. Some useful SARs were revealed Copyright
Different behavior of nitrenes and carbenes on photolysis and thermolysis: Formation of azirine, ylidic cumulene, and cyclic ketenimine and the rearrangement of 6-phenanthridylcarbene to 9-phenanthrylnitrene
Kvaskoff, David,Bednarek, Pawel,George, Lisa,Pankajakshan, Sreekumar,Wentrup, Curt
, p. 7947 - 7955 (2007/10/03)
Flash vacuum thermolysis (FVT) of 9-azidophenanthrene 8, 6-(5-tetrazolyl)phenanthridine 18, and [1,2,3]triazolo[l,5-f]phenanthridine 19 yields 9-cyanofluorene 12 as the principal product and 4-cyanofluorene as a minor product. In all cases, when the product is condensed at or below 77 K, the seven-membered ring ketenimine 24 is detectable by IR spectroscopy (1932 cm-1) up to 200 K. Photolysis of Ar matrix isolated 8 at λ = 308 or 313 nm generates at first the azirine 26, rapidly followed by the ylidic cumulene 27. The latter reverts to azirine 26 at λ > 405 nm, and the azirine reverts to the ylidic cumulene at 313 nm. Nitrene 9 is observed by ESR spectroscopy following FVT of either azide 8, tetrazole 18, or triazole 19 with Ar matrix isolation of the products. Nitrene 9 and carbene 21 are observed by ESR spectroscopy in the Ar matrix photolyses of azide 8 and triazole 19, respectively.
Design and synthesis of [(2,3-dichlorophenyl)piperazin-1-yl]alkylfluorenylcarboxamides as novel ligands selective for the dopamine D3 receptor subtype
Robarge,Husbands,Kieltyka,Brodbeck,Thurkauf,Newman
, p. 3175 - 3186 (2007/10/03)
The dopamine D3 receptor subtype has been recently targeted as a potential neurochemical modulator of the behavioral actions of psychomotor stimulants, such as cocaine. However, definitive behavioral investigations have been hampered by the lack of highly selective D3 agonists and antagonists. In an attempt to design a novel class of D3 ligands with which to study this receptor system, a series of chemically divergent compounds that possessed various structural features that exist within several classes of reputed D3 agents was screened and compared to the recently reported NGB 2904 (58b). On the basis of these results, a novel series of compounds was designed that included functional moieties that were required for high-affinity and selective binding to D3 receptors. All the compounds in this series included an aryl-substituted piperazine ring, a varying alkyl chain linker (C3-C5), and a terminal aryl amide. The compounds were synthesized and evaluated in vitro for binding in CHO cells transfected with human D2, D3, or D4 receptor cDNAs. D3 binding affinities ranged from Ki=1.4 to 1460 nM. The most potent analogue in this series, 51, demonstrated a D3/D2 selectivity of 64 and a D3/D4 selectivity of 1300. Structure-activity relationships for this class of ligands at D3 receptors will provide new leads toward the development of highly selective and potent molecular probes that will prove useful in the elucidation of the role D3 receptors play in the psychomotor stimulant and reinforcing properties of cocaine.
Reactions of 9-Substituted Fluorenide Carbanions with Allyl Chlorides by SN2 and SN2' Mechanism
Bordwell, Frederick G.,Clemens, Anthony H.,Cheng, Jin-Pei
, p. 1773 - 1782 (2007/10/02)
The average ratio of SN2 rate constants for benzyl chloride vs. allyl chloride reacting with 9-substituted fluorenide carbanions, 9-G-Fl- (G = Me, PhS, Ph o-tol, or t-Bu), in Me2SO solution is 2.3, which is close to the ratio previously observed for reactions of smaller nucleophiles with more localized charges, such as iodide ion, in various solvents.Broensted plots of log k vs. pKHA (both in Me2SO) are used to calculate reactivity values (r) for 9-G-Fl- ions of the same basicity reacting with allyl chloride.The r values reveal the same order of steric effects for G in these SN2 reactions as was found previously for benzyl chloride, i.e., Me - ions were found to increase progressively and appreciably with γ-methyl substitution, i.e., CH2=CHCH2Cl (1) , MeCH=CHCH2Cl (4) , Me2C=CHCH2Cl (5), whereas the Broensted β values decreased progressively.The second-order rate constants for reactions with families of 9-G-Fl- ions were found to follow a somewhat different pattern for α-methyl substitution, i.e., CH2=CHCH2Cl (1) > CH2=CHCH(Me)Cl (2) CH2=CHC(Me)2Cl (3); the rate differences were small, but the β values again decreased progressively.Product studies indicated that 1 reacts with 9-G-Fl- ions by an SN2 mechanism but that 2 gives SN2' products in a amounts increasing along the series G = Me, Ph, o-tol, t-Bu; 3 appears to give only SN2' products.The rates of reactions of 9-CN-Fl- and 9-CO2MeFl- ions with 3 to form SN2' and SN2 products are independent of the carbanion concentration.The first-order reaction of 9-CN-Fl- ion with t-BuCl in MeOH gives 17percent yield of 9-CN-9-t-BuFl.Entalpies of activation for SN2 reactions of 9-G-Fl- ions reacting with 5 are 7-9 kcal/mol lower, and entropies of activation are 18, or more, eu units less positive than for SN2' reactions of 9-G-Fl- ions with 3.Mechanism for SN2' reactions are discussed in light of these findings.
Cation-Anion Combination Reactions. 21. Reactions of Thiolate Ions, Cyanide Ion, and Amines with Cations and Carbonyl Compounds in Me2SO Solution
Ritchie, Calvin D.,Verth, J.E. Van,Virtanen, P.O.I.
, p. 3491 - 3497 (2007/10/02)
The pKa's of three alkanethiols and of two ammonium ions, and the rates of reactions of the thiolates, amines, and of cyanide ion with Malachite Green, Crystal Violet, 2,4-dinitrophenyl acetate, and 9-acetyl-9-cyanofluorene, all in Me2SO solution, have been measured.The pKa's of the thiols in Me2SO, compared with those in water, indicate important hydrogen bonding of water to the thiolates.The reactions of nucleophiles with both the triarylmethyl cations and 2,4-dinitrophenyl acetate have rate constants that are greater in Me2SO than in water.The solvent effects on rates are compared with solvent effects on equilibrium constants to arrive at measures of the progress of the transition states toward products as "seen" by solvent.These measures are not in accord with other measures, such as Broensted slopes, possibly indicating that transition states are not solvated in a manner suggested by stable molecule analogues.The pattern of nucleophilic reactivities toward 9-acetyl-9-cyanofluorene is different from that toward 2,4-dinitrophenyl acetate.A possible rationalization involving concerted reactions of 2,4-dinitrophenyl acetate, but stepwise reactions of the ketone, is discussed.
