Experimental studies of the anomeric effect. Part VI. Ring inversion equilibria in cyclohexane, tetrahydropyran and piperidine rings substituted by a carbomethoxy or a cyano group.

Booth, Harold Simmons; Je, Dixon; Khedhair, Khedhair A.

doi:10.1016/s0040-4020(01)89862-8

Cited by 30 publications

(22 citation statements)

References 26 publications

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“…6 Based on the integration of 13 C resonances (155-180 K), and line broadenings of these at higher temperatures (190-220 K), it was deduced that the cyano substituent preferred an axial orientation, with an equilibrium constant K eq/ax ranging from 0.20 at 155 K to 0.25 at 200 K. As our old observations were in accord with these results, we concentrated on re-examining the behaviour of the sulfur-and seleno-analogs (3 and 4, respectively), both of which had subsequently been described by other work- ers, 19,20 albeit without comment on their stereochemical preferences.…”

Section: Resultsmentioning

confidence: 99%

“…1 H NMR d H (ppm): 11.11 (1H, br s), 4.23 (1H, dd, J = 6.6 and 7.9 Hz) 3.37 (2H, t, J = 6.6 Hz), 2.05 (2H, m), 1.87 (2H, m), 1.85 (1H, m), 1.64 (1H, m). 13 (±)-Thiane-2-carboxylic acid (6) This was prepared from (±)-2,6-dibromohexanoic acid (5) according to Roush et al 18 and obtained as a colourless viscous oil. 1 …”

Section: Methodsmentioning

confidence: 99%

“…While the anomeric effect is well-established for n O ?s Ã CX 2,6-11 and n N ?s Ã CX , 6 where X is any electronegative group, including CN, its importance in the case for the donor being a second or higher row element, e.g., n S ?s Ã CX , is less certain. [10][11][12] Cyclohexane derivatives possessing X substituents adjacent to S also preferentially adopt the C-X axial orientation.…”

Section: Introductionmentioning

confidence: 99%

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Concerning the conformational preferences of the 2-cyano derivatives of oxane, thiane, and selenane

et al. 2010

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This paper investigates the origin of the anomalous anomeric effect in merosinigrin, a 2-cyanothiane in which the cyano group is axial as expected for the anomeric effect, but in which bond distances are opposite to that expected from the n S ?s Ã CÀCN orbital interaction, which underlies the classical anomeric effect. The model compounds, 2-cyanooxane, 2-cyanothiane, and 2-cyanoselenane, were synthesized and studied both experimentally and computationally. Both the thia and selena systems displayed an even higher preference for the axial conformation than the oxa system but also exhibited the bond length anomalies found previously in merosinigren. Natural bond order (NBO) analysis of the B3LYP/6-311+G(3df,2p) wave functions of the axial and equatorial forms of the three systems confirmed a weakening of the n?s* orbital interaction in the O, S, and Se series, and a strengthening of a s-p*(CN) interaction that explains the bond length reversals observed in the S and Se systems. It also revealed a new mechanism, n?p*, namely, a through-space interaction between the nonbonded lone pair electrons of the heteroatom and the p* orbital of the cyano group, which selects for the axial conformation.Résumé : Dans ce travail, on recherche l'origine de l'effet anomère anormal dans la mérosinigrine, un 2-cyanothiane dans lequel le groupe cyano est axial, tel qu'on pourrait s'y attendre en raison de l'effet anomère, mais dans lequel les longueurs des liaisons sont à l'inverse de celles attendues sur la base d'une interaction orbitalaire n S ?s Ã CÀCN qu'on retrouve dans l'effet anomère classique. On a synthétisé les composés modèles, 2-cyanooxane, 2-cyanothiane et 2-cyanolélénane et on les a étudiés tant d'un point de vue expérimental que théorique. Les systèmes thia et séléna présentent tous les deux une préférence pour la conformation axiale qui est supérieure à celle du système oxa, mais ils présentent aussi les anomalies de longueurs des liaisons qui ont été observées antérieurement dans la mérosinigrène. Une analyse de l'ordre naturel de liaison (ONL) des fonctions d'onde B3LYP/6-311+G(3d,2p) des formes équatoriales et axiales des trois systèmes confirme un affaiblissement de l'interaction de l'orbitale n?s* dans les séries O, S et Se et un affermissement de l'interaction s-p*(CN) qui explique les inversions des longueurs des liaisons observées dans les systèmes S et Se. Elle met aussi en évidence un nouveau mécanisme, n?p*, à savoir une interaction à travers l'espace entre la paire d'électrons non liée de l'hétéroatome et l'orbitale p* du groupe cyano qui choisit la conformation axiale.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Concerning the conformational preferences of the 2-cyano derivatives of oxane, thiane, and selenane

et al. 2010

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“…Although this conformer places the ester and nitro substituent in axial positions, the hyperconjugation between the lone pair on nitrogen and the anti-bonding orbital of the C-CO2Et bond provides additional stabilization (n-* interaction). 19 NOE contacts between CHNO2 its two vicinal protons were observed, but that between ArCH and CHCO2Et was not. This conformation would result in two small coupling constants to CHNO2 and in the 1 H NMR spectrum these were not resolved, giving rise to a broad singlet instead.…”

Section: Optimisation Of Nitro-mannich/reductive Cyclisation Sequencementioning

confidence: 89%

“…Chromatography of reside on silica gel, using 30% EtOAc in hexane, gave 10 (20.0 mg, 83% overall) as a colourless oil. Rf (30% EtOAc in hexane) 0.32; FTIR (neat, cm -1 ) 2984, 2908,1742,1697,1554,1506,1491,1446,1235,1205,1170,1147; HRMS (ESI-TOF) ; 1 H NMR (400 MHz, CDCl3) a mixture of diastereomers, dr 85:15; major isomer:  6.77 (1H, d, J = 7.8), 6.70-6.59 (2H, m), 5.96 (2H, s), 5.89 (1H, t, J = 1.7), 5.49-5.42 (1H, m), 4.47-4.17 (3H, m), 3.39 (1H, ddd, J = 14.3, 13.0, 2.9), 3.19 (1H, dt, J = 13.3, 3.4), 2.67 (1H, qd, J = 13.3, 4.4), 1.92-1.78 (1H, m), 1.36 (3H, t, J = 7.1); 13 C NMR (101 MHz, CDCl3) δ 166.0 (C), 157.2 (q, J = 37.2, C(O)CF3), 148.3 (C), 147.6 (C), 130.9 (C), 120.5 (CH), 116.3 (q, J = 287.4, CF3), 108.8 (CH), 107.5 (CH), 101.4 (CH2), 84.5 (CH), 63.5 (CH2), 55.5 (CH), 43.4 (CH2), 41.2 (CH), 23.8 (CH2), 14.2 (CH3); 19 F NMR (282 MHz, CDCl3) δ -67.90 (minor isomer), -68.97 (major isomer). HRMS (ESI-TOF, m/z) calcd.…”

Section: Ethyl 4-(benzo[d][13]dioxol-5-yl)-3-nitro-1-(222trifluoroacetyl)piperidine-2-carboxylate (10)mentioning

confidence: 99%