55832-04-7Relevant articles and documents
Regioselective Synthesis of Trisubstituted Quinoxalines Mediated by Hypervalent Iodine Reagents
Ito, Ryota,Miura, Kasumi,Suzuki, Noriyuki,Suzuki, Yumiko,Takehara, Ren
, p. 16892 - 16900 (2021/12/06)
A facile and regioselective synthesis of quinoxalines, an important motif in medicinal chemistry and materials sciences, was developed. Despite their prospective utility, the regioselective preparation of trisubstituted quinoxalines has not been previously established. In the reported system, hypervalent iodine reagents catalyzed the annulation between α-iminoethanones ando-phenylenediamines in a chemo/regioselective manner to afford trisubstituted quinoxalines. Excellent regioselectivities (6:1 to 1:0) were achieved using [bis(trifluoroacetoxy)iodo]benzene and [bis(trifluoroacetoxy)iodo]pentafluorobenzene as annulation catalysts.
N-arylbenzonitrilium ions. Photochemical generation and effect of substituents in the phenyl rings on lifetimes in water and reactivity with azide ion
Ruane, Patrick H.,Ahmed, Abid R.,McClelland, Robert A.
, p. 312 - 317 (2007/10/03)
Nitrilium ions Ar-C≡N+-Ar′ have been studied by laser flash photolysis in aqueous solutions containing 20% acetonitrile. The cations were generated by photoheterolysis of benzimidate esters Ar-CZ=N-Ar′ (Z = -OC6H4-4-CN) with 4-cyanophenoxide as the photochemical leaving group. Rate constants for the reaction with water (kw), azide ion (kaz) and hydroxide (kOH) were measured. The cation Ph-C≡N+-Ph is only 50-fold shorter lived in water compared to Ph-C≡N+-iPr (2); thus the effect of replacing an N-alkyl group with N-phenyl is modest. These two cations are also shown to have similar lifetimes to iminium analogs, e.g. Ph-CH=N+ (Me)-Ph. Thus, addition of water to analogous sp and sp2 hybridized systems occurs at a similar rate, and the increased steric access to the nitrilium plays at most a modest role. For the series where substituents in Ar′ were varied with Ar equal to phenyl, the Hammett plot for log kw correlated with σ, with ρ = - 1.4. For the series where Ar was varied, the data correlated much better with σ+, although ρ+ was only -0.6. This remarkably small effect of substituents in Ar constrasts with the effects seen in benzylic carbocations, but is consistent with the nitrilium structure, with most of the positive charge located on the nitrogen. Rate constant ratios kaz:kw, including the N-alkylnitrilium ion 2, are constant at ～104, with values of kaz well below the diffusion limit, even for the most reactive nitrilium ions. This is very different behaviour from that of carbocations and arylnitrenium ions of similar lifetimes in water. For these cations the rate constants kaz would be at or at least approaching the diffusion limit.
