¹³C shieldings in syn and anti aldimines and ketimines

Abstract

FUMINORI AKIYAMA, and NOEMI CHUAQUI-OFFERMANNS. Can. J. Chem. 59,705 (1981).The I3C chemical shifts in a variety of aldimines and in both acyclic and cyclic ketimines have been examined. A comparison of the shieldings at the a carbons in syn versus anti stereoisomers shows a consistent upfield shift of 8-11 ppm in the syn isomer. The greater magnitude found in imines vs. oximes or hydrazones is a clear indication of a steric origin for the differential shieldings. The shifts in the imines of cyclohexanones exhibited stereochemically dependent effects of methyl substitution, very similar to those in analogous oxime and hydrazone derivatives. Chemical shift differences in the syn isomers of the a-phenethylimines of chiral aldimines and ketimines allow a facile measurement of diastereomer ratios for such compounds.ROBERT R. FRASER, JACQUES BANVILLE, FUMINORI AKIYAMA et NOEMI CHUAQUI-OFFERMANNS. Can. J. Chem. 59,705 (1981). On a examine les deplacements chimiques du I3C de diverses aldimines et des cetimines acycliques et cycliques. En comparant le blindage au niveau des carbones en positions a des stCrCoisomkres syn et anti, on constante un dtplacement vers les champs forts de 8-1 1 ppm en faveur de I'isomere syn. La valeur plus forte observee pour les imines par rapport icelle des oximes ou des hydrazones est une nette indication de I'origine sttrique des blindages differentiels. Les deplacements observes dans les imines de cyclohexanones ont des effets qui dependent stereochimiquement de la substitution par les methyles et qui sont trks semblables a ceux des derives analogues d'oximes et d'hydrazones. Les differences de deplacement chimique des isomkres syn desa-phenethylimines d'aldimines et de cetimines chirales permettent de mesurer facilement les rapports de diastereoisomkres dans de tels composes.[Traduit par le journal]The 13C spectral characteristics of aldehydes and ketones have been thoroughly studied (1, 2) and more recently many of their carbonyl derivatives including oximes (3-9, hydrazones (5, 6), and oxime ethers (6) have received considerable attention. Another class of nitrogen-containing carbonyl derivatives which has not been studied to any significant extent is the imines, data on only a few aryl(7) and a few anti aldimine derivatives (8) having been reported. During the course of our studies on the alkylation of ketimines (9, 10) and aldimines (11, 12) we have had the opportunity to record a large number of spectra of both the syn and anti isomers. In this paper we wish to describe the spectral characteristics of a number of representative examples in order to demonstrate the capability of 13C nmr to reveal both configurational and conformational information for this class of compounds. In addition, the comparison of configurational effects with those previously observed in other species provides clear evidence for the dominance of steric factors in causing the large --differential syn-anti shifts. ExperimentalThe imines described herein have all been synthesized either from the parent ketone...

Stereochemical analysis ofN-cyclohexylidene-N-(1-phenylethyl)amine derivatives

“…Both the cyclohexanones and the amines are commercially available products. The physical and spectroscopic properties are in good agreement with previous reports: 1, 6,7 as well; both products showed NMR spectra identical with the one prepared from the racemic mixture.…”

“…To our knowledge, only the absolute configurations of Ncyclohexylidene-1-phenylethylamine (1) and some isomers of N-(2-methylcyclohexylidene)-1-phenylethylamine (2) prepared by stereoselective alkylation, have been determined by means of chiroptical methods 6 and their relative configuration established by NMR. 7 In this paper we report the 1 H, 13 C and 15 N NMR assignment of imines 1-5 (Scheme 1). Although the structures of these compounds have been described as simple, they possess some symmetry elements that require more detailed analysis.…”

“…This assignment is in agreement with previous reports. 7,8,10 The 15 N NMR chemical shifts (Table 3) reflect a dependence on the configuration of the molecules; however, the shift difference between isomers is less than 0.4 ppm (Scheme 2). In derivative 2, only the signals for the main isomers product were observed.…”

13C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

“…Imines 1-10 were synthesized from the parent aldehyde or ketone and primary amine as described previously (5). For the ketimine derived from tert-butyl amine (60 mmol scale) pentane (10mL) was used in place of ether and two drops of pyridine were added to shorten the reaction time to 16h.…”

Grassypeptolides F and G, Cyanobacterial Peptides from Lyngbya majuscula

“…The strongly deshielded chemical shifts of the methine carbons C-22 and C-29 (δ C 77.6 and 79.4, respectively) were consistent with cyclic secondary ketimine attachment at both centers in addition to the down-field effect of the adjacent carbonyls (C-21 and C-28, respectively). 8 The molecular formula indicated the presence of two sulfur units in the molecule. One-bond carbon–proton coupling constants ( 1 J CH ) increase with substitution of electron-withdrawing groups (viz.…”