Conformational analysis. XVIII. 1,3-Dithianes. Conformational preferences of alkyl substituents and the chair-boat energy difference

. Can. J. Chem. 64, 2142Chem. 64, (1986. The conformational and dynamic properties of 1,5-benzodithiepin (I), its 3,3-dimethyl (2), 3-methyl (3), and 3-methoxy (4) derivatives have been investigated by high-field 'H and I3C dynamic nuclear magnetic resonance mcthods. Analyses of the spectra at low temperatures indicate that, in CS2, both 1 and 2 exist as a mixture of C and TB forms (97:3 for 1; 63:37 for 2). In contrast, both 3 and 4 exist as a mixture of three equilibrating conformations C,, C,, and TB in ratios of 55:25:20 and 88:8:4 respectively. Comparison with analogues derived from 1,5-benzodioxepins (la-4a) indicates that the replacement of 0 by S decreases the amount of the TB form for all four compounds studied. The observation that C, is the most abundant form for 4 while it is not observed for 4n can be explained by a repulsive S/O gauche interaction in 4 compared to an attractive 010 interaction in 4a. Chem. 64, 2142Chem. 64, (1986.Faisant appel B des mCthodes de rmn du 'H et du "C B hauts champs, on a CtudiC les propriCtCs dynamiques et conformationelles de la benzodithiepine-1,s (1) et de ses dCrivCs dimCthy1-3,3 (2), methyl-3 (3) et mCthoxy-3 (4). L'analyse des spectres mesurCs dans le CS2, a basse tempkrature, indiquent que les composCs 1 ainsi que 2 existent B I'Ctat de mClange des formes C et TB (97 :3 dans le cas du composC 1 et 63 : 37 dans le cas du compose 2). Par ailleurs, les composCs 3 and 4 existent tous les deux a 1'Ctat de mClange des trois conformations a l'kquilibre, C,. C, et TB dans des proportions respectives de 55 :25 : 20 et 88: 8:4. Une comparaison avec des analogues provenant des benzodioxipines (la-4a) indiquc que. dans chacun des composCs CtudiCs, le remplacement d'un oxygkne par un soufre diminue la proportion de la forme TB. Le fait que la forme C, soit la forme la plus abondante dans le composC 4 alors que l'on n'observe pas sa prCsence dans le cas du compose 4a pourrait &tre expliquC par la prCsence d'un interaction gauche S/O rCpulsive dans le composC 4 alors que, dans le composC 4a, il existerait une interaction 010 attractive.[Traduit par la revue]Pursuing our study of seven-membered heterocyclic compounds related to the 1,5-benzodioxepin ( l a ) family, which recently revealed novel and diversified conformational features for some 3-substituted derivatives (1, 2), we have sought to identify the conformational preferences of analogous compounds derived from 1,5-benzodithiepin (1). Comparison of the results from the two series should provide valuable information on the origin of the underlying forces, which appear to involve strong electrostatic interactions in addition to steric ones. Indeed, it has been pointed out that the substitution of oxygen by sulfur significantly modifies the gauche effect in six-membered heterocycles so that the 010 gauche interaction present in 4 a should be attractive (2) while the O / S interaction that would exist in 4 should be repulsive (3).1 : X = S ; R = R r = H l a : X = 0; K = R' = H 2: X = S; R = R' = CH3 3: X = S; R = CH3, ...

Section: Origin Of the Conformation Preferencescontrasting

confidence: 48%

High-field proton and carbon-13 nuclear magnetic resonance studies of the conformational dynamic properties of seven-membered rings. 1,5-Benzodithiepin and 3-substituted derivatives

Menard¹,

St‐Jacques²

1986

“…Analogous effects were observed upon irradiation of the H-4, signals of either conformer (entries 5,6). Saturation transfer effects between H-2's of the two conformers (entries 7,8) were also observed; in addition, irradiation of H-2 in the spectrum of the minor conformer l a also resulted in detectable magnetization transfer effects on H-4, of the major isomer le. The latter effect results from magnetization transfer via exchange of H-2, in l a with H-2, in l e , coupled with a relayed nOe effect between H-2, and H-4, in l e .…”

Section: H4alm1nlmentioning

confidence: 91%

A dynamic NMR study of the nitrogen lone pair orientation in 2-benzoyl-5-methyl-5-aza-1,3-dithiacyclohexane

Pinto¹,

Johnston²,

Nagelkerke³

et al. 1989

. 67,2067 (1989).Nuclear Overhauser enhancement difference experiments and magnetization transfer experiments on 2-benzoyl-5-methyl-5-aza-l,3-dithiacyclohexane 1 at 186 K show conclusively that the N-methyl group adopts a preferred axial orientation. The result has implications for evaluation of the origin of the anomeric effect in this and related compounds. The free energy of activation for ring interconversion in 1 is estimated by spin saturation transfer experiments to be 10.7 * 0.4 kcal mol-'.

“…Compounds 6-9 were prepared by standard procedures (34,(36)(37)(38)(39)(40)(41)(42) and gave satisfactory mass and 'H nmr spectra (28,(43)(44)(45)(46)(47). These were repeatedly calibrated at 5-Hz intervals in the frequency sueep mode of a n HA100 spectrometer at a probe temperature of 305 5 1 K. The spectral dispersion was 1 Hz:' cm and sweep rates were 0.02 and 0.01 Hz/s.…”

Section: Methodsmentioning

confidence: 99%

The conformational preference and barrier to internal rotation of an equatorial 3,5-dichlorophenyl group by the J method. Derivatives of cyclohexane, 1,3-dithiane, 1,3-dioxane, and 1,3-dioxolane

Schaefer¹,

Niemczura²,

Danchura³

1979

(1979) We report the preparation and the analysis of the phenyl ring proton magnetic resonance spectra of 3,5-dichlorophenylcyclohexane and of the 2-(3,5-dichlorophenyl) derivatives of 1,3-dioxane, 1,3-dithiane, and 1,3-dioxolane. With the exception of the dioxolanes these compounds exist predominantly as the equatorial isomers. The J method is used to show that the phenyl moiety prefers the conformation in which the x C-H bond lies in the phenyl La faible valeur pour la barriere, dans le derive dioxanne-1,3, est en bon accord avec des calcuis de mtcanique molCculaire et avec les resultats d'etudes calorimetriques et de diffraction de rayons-X sur le phenyl-2 dioxanne-1,3 equatorial.[Traduit par le journal]