ABSTRACT
Kinetics of the reactions of aryldiazomethanes (ArCHN2) with benzhydrylium ions (Ar2CH+) have been measured photometrically in dichloromethane. The resulting second-order rate constants correlate linearly with the electrophilicities E of the benzhydrylium ions which allowed us to use the correlation lg k = sN( N + E) (eq 1) for determining the nucleophile-specific parameters N and sN of the diazo compounds. UV-vis spectroscopy was analogously employed to measure the rates of the 1,3-dipolar cycloadditions of these aryldiazomethanes with acceptor-substituted ethylenes of known electrophilicities E. The measured rate constants for the reactions of the diazoalkanes with highly electrophilic Michael acceptors ( E > -11, for example 2-benzylidene Meldrum's acid or 1,1-bis(phenylsulfonyl)ethylene) agreed with those calculated by eq 1 from the one-bond nucleophilicities N and sN of the diazo compounds and the one-bond electrophilicities of the dipolarophiles, indicating that the incremental approach of eq 1 may also be applied to predict the rates of highly asynchronous cycloadditions. Weaker electrophiles, e.g., methyl acrylate, react faster than calculated from E, N, and sN, and the ratio of experimental to calculated rate constants was suggested to be a measure for the energy of concert Δ Gconcert = RT ln( k2exptl/ k2calcd). Quantum chemical calculations indicated that all products isolated from the reactions of the aryldiazomethanes with acceptor substituted ethylenes (Δ2-pyrazolines, cyclopropanes, and substituted ethylenes) arise from intermediate Δ1-pyrazolines, which are formed through concerted 1,3-dipolar cycloadditions with transition states, in which the C-N bond formation lags behind the C-C bond formation. The Gibbs activation energies for these cycloadditions calculated at the PCM(UA0,CH2Cl2)/(U)B3LYP-D3/6-31+G(d,p) level of theory agree within 5 kJ mol-1 with the experimental numbers showing the suitability of the applied polarizable continuum model (PCM) for considering solvation.
ABSTRACT
The kinetics of the reactions of the trans-ß-nitrostyrenes 1a-f with the acceptor-substituted carbanions 2a-h have been determined in dimethyl sulfoxide solution at 20 °C. The resulting second-order rate constants were employed to determine the electrophile-specific reactivity parameters E of the trans-ß-nitrostyrenes according to the correlation equation log k(2)(20 °C) = s(N)(N + E). The E parameters range from -12 to -15 on our empirical electrophilicity scale (www.cup.lmu.de/oc/mayr/DBintro.html). The second-order rate constants for the reactions of trans-ß-nitrostyrenes with some enamines were measured and found to agree with those calculated from the electrophilicity parameters E determined in this work and the previously published N and s(N) parameters for enamines.
ABSTRACT
In the title compound, C(14)H(17)NO(3), the plane of the phenyl ring and the least-squares plane of the cyclo-hexyl moiety enclose an angle of 89.14â (6)°. The cyclohexyl ring adopts a chair conformation. In the crystal, the molecules are linked by weak C-Hâ¯O bonds, with each of the nitro-O atoms accepting two such interactions.
ABSTRACT
Indole aziridines and their hydroxyl derivatives have been used for the preparation of a small library of novel functionalized bisindoles. Diversification of these building blocks by solvent-free C-C-bond formation on solid support yielded annulated Hymenialdisine analogues under mild reaction conditions. Indoles as C-nucleophiles form potentially pharmacologically active bisindoles through an electrophilic aromatic substitution pathway in good to excellent yields. Further transformations of the indole aziridines with H-, N-, and O-nucleophiles demonstrate their versatility as key intermediates in diversity oriented synthesis. The hydroxyl precursor leads also to unsymmetrical bisindoles under similar reaction conditions. Important intermediates and final library compounds were confirmed by X-ray analysis. Theoretical studies on these systems show the possible cationic intermediate in the substitution pathway.
