Substituent effects on ¹³C chemical shifts of 1‐arylsulphonyl‐2‐arylaziridines

Abstract

Carbon-13 chemical shifts of l-phenylsulphonyl-2-phenylaziridine and several of its m-and psubstituted derivatives have been determined. The substituent chemical shift (SCS) effects on the benzylic carbon C-2, and on the methylene carbon C-3 have been satisfactorily correlated with Hammett substituent parameters (a) for variation of the C-Zaryl ring substituent (with a arylsulphonyl ring), and for analogous variation of the arylsulphonyl ring (with a given C-Zaryl ring). The results reveal an inverse C-Zaryl SCS effect on C-2, whereas the effect on C-3 is nosubstituents on the arylsulphonyl ring have a normal effect on both C-2 and C-3, for which the SCS is to higher frequency with increasing electron-withdrawing power of the substituent.In conjunction with a continuing investigation of the kinetics of ring-opening reactions of three-membered heterocycles, we have had occasion to record the 13C NMR spectra of a wide range of l-arylsulphonyl-2-arylaziridines (A). The results are of particular interest since there have been relatively few reports of I3C NMR spectra for series of three-membered heterocycles.' Further, our investigation of the relationship between Hammett substituent parameters (a, and a , ) and the I3C chemical shifts of C-2 and C-3 has revealed an inversion of the dependence on substituents X for the two atoms; thus, an increase in the electron-withdrawing power of X causes the I3C resonances of C-2 and C-3 to move to lower frequency and to higher frequency, respectively. The chemical shift values for C-2 and C-3 are subject to almost identical downfield displacements with an increase in the electron-withdrawing power of substituent Y. EXPERIMENTAL MeasurementsC NMR spectra were determined in CDCl, (0.5 mmol cm-') containing 2.5% v/v of T M S as reference, on a JEOL FX90Q spectrometer fitted with a multinuclear probe insert operating at 22.50 M H z with deuterium lock (CDC1, signal) and resolution stabil- iser; conventional wide-band proton noise and offresonance decoupling modes were used in conjunction, where necessary, with the usual gated (NOE retained) coupled mode in the course of spectral assignment. A n excitation pulse of 10 p s (a = 30") and a repetition time of 1.182s were used with a 600Hz spectral width and 8K data table; between 1000 and 10 000 scans were accumulated as required. Chemical shifts are expressed as G(ppm) with respect to internal TMS . Compounds 1-Arylsulphonyl-2-arylaziridines (A)were prepared by base-induced cyclization of the corresponding N-arylsulphonyl-1-aryl-2-bromoethylamines. The general procedures for the formation and dehydrobrominative cyclization of the bromoalkylsulphonamides are to be published in Synthesis. RESULTS AND DISCUSSIONThe 13C signals for the aziridines A were readily assigned using the known chemical shift rules2 in conjunction with observations of the off -resonance decoupled spectra. The results are listed in Table 1, and details of the Hammett correlations observed between the varying substituent parameter ax (or a,) and the substituent ch...

Trifluoromethanesulfonamides and Related Compounds

“…189 It is noteworthy that simple NMR and elemental analysis is insufficient to prove the formation of aziridines. To distinguish them from their dimers, piperazines, X-ray analysis, or, at least, measuring of 1 J CH constants (which in aziridines are much higher than in unstrained compounds, 170−180 versus 140−150 Hz) 190 is required.…”

The Reactions of Alkenes with Phenyl-N-triflylimino-λ3-iodane: Solvent and Oxidant Impact

“…The structure of aziridine 10 was proved by IR and NMR spectroscopy and confirmed by HRMS data. In particular, the values of the 1 JCH constants in the aziridine moiety are known to be much larger than in saturated aliphatic compounds and lie in the range of 170-180 Hz [32,33,34]. The measured value of 1 JCH in product 10 is 177 Hz, which unambiguously proves its structure.…”

Formation of 2,6-diphenyl-1,4-bis(trifluoromethylsulfonyl)piperazine in the reaction of styrene with trifluoromethylsulfonylnitrene

“…In the proton-coupled 13 C NMR spectrum, the CH signal was split into a doublet with 1 J CH = 154.4 Hz, and the CH 2 signal was split into 8 lines due to coupling with diastereotopic methylene protons ( 1 J CH = 142.2, 144.0 Hz) and CH proton ( 2 J CH = 4.1 Hz). The observed direct coupling constants 1 J CH are much smaller than those typical of aziridines (>170 Hz [23]). Likewise, the 13 C NMR spectrum of the crude product obtained by aziridination of styrene with methanesulfonamide according to [3] contained multiplet signals with coupling constants 1 J CH of 155-157 Hz.…”