Nuclear magnetic resonance investigations of carbonium ion intermediates. Part IV. Study of the intermediates involved in the reaction between carboxamides and Lewis acids (extended Vilsmeier reaction) by 1H and 13C nuclear magnetic resonance spectroscopy

Total Synthesis of (±)-Eucophylline. A Free-Radical Approach to the Synthesis of the Azabicyclo[3.3.1]nonane Skeleton

“…In order to obtain information regarding the mechanism of the coupling mentioned above, bicyclic lactam 16 was treated with POCl 3 (2.2 equiv) in CH 2 Cl 2 under reflux for 3 h. This led, after basic treatment, to α-chloroenamine 18 (60% yield), the structure of which could be established unambiguously through extensive 1 H and 13 C NMR studies. In contrast with reported α-chloroenamines, 18 was found to be remarkably stable . The treatment of 18 with trifluoroacetic acid (1 equiv) did not generate the α-choroiminium, but led to the kinetic protonation at the nitrogen center with the formation of the α-chloro-enaminium salt 20 in quantitative yield.…”

“…Surprisingly, reaction of 18 with 6b in the absence of TFA or with 10 mol % of 2,6-di- tert -butyl­pyridine also led to amidine 17b in good yields. α-Chloroenamines are known to react with nucleophiles, including amines via a ketene-iminium intermediate, which is unlikely with bicyclic 18 . Although further studies will be required to firmly establish the mechanism of this coupling, strong coloration observed upon mixing 18 and 6b might be indicative of a single electron-transfer initiation process occurring under neutral or basic conditions.…”

Influence of phospholipid peroxidation on the phase behavior of phosphatidylcholine and phosphatidylethanolamine in aqueous dispersions

“…The new carbon resonance peak at 44.2 ppm reached an intensity of 27% as related to the glycerol C-2 atom resonance. This peak position (44.2 ppm) is typical of a -C-N= carbon atom in a Schiff base (Martin et al, 1976). These results, together with the decrease of reactivity of the ethanolamine head group toward trinitrobenzenesulfonic acid, strongly suggest the formation of Schiff bases between about 30% of the PE molecules and aldehydes (e.g., malondialdehyde) derived from the peroxidized acyl chains.…”

On the Formation and 1H NMR-spectroscopic Characterization of N,N-Diaryl-substituted Formamide Chlorides

“…Formamide chlorides 3a and 3b exhibit, similar to other N, N-dialkyl substituted formamide chlorides [9], in the 1 H NMR spectra characteristic singlets at δ ≈ 10 ppm, and a signal in the same region was thus expected also for the proton at the methine-iminium moiety in 3c. To our surprise, this was not the case, however.…”

“….93 a [9,10] 7.92 b [11] 8.02 c [25] 7.95 d [25] 10.10 a [9,10] 11.08 b [11] 9.21 d [15] 9.21 d [16] 10.56 d [17] 10.62 d [18] 10.32 d [19] 7.40 d [20] b 8.48 [21] 8.53 c [25] 8.48 d [25] 9.51 a [9] 9.36 / 9.46 b [14] 9.64 e [12] 11.17 d [18] 11.22 d [22] 8.10 d [13] c 8.55 d [23] 8.64 d [24] 7.60 d , f 10.0 d [16] 8.67 d [20] 11.75 d [16] 8.18 d [25] …”