Stereochemical studies—XX

Zefirov, N. S.; Gurvich, L. G.; Shashkov, A. S.; Krimer, M. Z.; Vorob'eva, E. A.

doi:10.1016/0040-4020(76)80074-9

Cited by 98 publications

(36 citation statements)

References 73 publications

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“…The second transition is more difficult, because the form 9B must be additionally destabilized by a substantial gaucherepulsion between two equatorial atoms of sulfur as it was found in trans-1-RS-2-R′S-cyclohexanes. 36,37 This can explain why the reaction proceeds only up to thiirane in the case of sterically loaded epoxide 1l (entry 12 in Table 2), or can be stopped at the thiirane step in the case of epoxides 1i and 1r (entries 9 and 18). Similarly, steric strain in reaction intermediates prevented transformation of steroid thiiranes into trithiocarbonates (with one questionable exception).…”

Section: Bmentioning

confidence: 99%

Convenient synthesis of 1,3-dithiolane-2-thiones: cyclic trithiocarbonates as conformational locks

Dotsenko¹,

Zhao²,

Franz³

et al. 2014

Arkivoc

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A series of novel 1,3-dithiolane-2-thiones, or cyclic trithiocarbonates, has been prepared by a new simple procedure: a treatment of the corresponding epoxides with the commercially available potassium ethyl xanthogenate, KSC(S)OEt. The stereochemistry of the products was determined by 1 H NMR and in some cases by single-crystal X-ray data. Cyclohexane-based 1,3-dithiolane-2-thiones revealed a trans-fusion of the carbo-and hetero-cycles. The products obtained from the mono-substituted cyclohexene oxides demonstrated an axial position of the substituents. Thus the epoxide transformation into trithiocarbonate can be used as a method for locking cyclic compounds in unstable conformations.

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Section: Bmentioning

confidence: 99%

Convenient synthesis of 1,3-dithiolane-2-thiones: cyclic trithiocarbonates as conformational locks

Dotsenko¹,

Zhao²,

Franz³

et al. 2014

Arkivoc

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“…The γ-butyrolactones studied in this work (Table 1) can be classified into three groups: disubstituted (1-6), trisubstituted (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), and tetrasubstituted (23-36) (Scheme 2). All side-chain rotamers have been generated and geometry-optimized.…”

Section: Computational Materials and Techniquementioning

confidence: 99%

“…When strongly favors quasi-equatorial (to be referred below simply as equatorial and quasi-axial as axial) orientation to form hydrogen bonding with the carbonyl oxygen atom which extends the protonaccepting lone-pair in the average plane of ester group. On the other hand, axial orientation is favored for an OH group attached to positions 3 or 4, because of the gauche [12][13][14] and anomeric [15][16][17][18] effects. The relative importance of these three different types of effects remained unknown in our previous work.…”

Section: Disubstituted γ-Butyrolactones 1-6mentioning

confidence: 99%

Vicinal ring H/H Coupling Constants of γ‐lactones containing two hydroxyl groups

Dinarés

Entrena

Jaime

et al. 1997

Elect J Theoret Chem

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“…The fact that the C, form is found to be predominant for these three compounds (in the two solvents used), as well as published considerations (6,8), suggests that part of the stabilization of the C, form should arise from a repulsive gauche effect. Accordingly, the bond-antibond orbital interactions will be examined to identify the origin of the repulsive feature.…”

Section: Discussionmentioning

confidence: 85%

“…For example, the data in Table 2 (6,(14)(15)(16) show that the equatorial preference of cyclohexylmethyl sulfide is higher than that of the heavy halogen and methoxy substituents. But when the SCH3 substituent interacts with a vicinal polar 0CH3 substituent, as in trans-1 -methylthio-2-methoxycyclohexane, a conformational population change occurs that is larger than predicted on steric grounds (32% of axial conformation in CC14, -AGO = 0.4 kcal/mol) (6).…”

Section: Discussionmentioning

confidence: 99%

Repulsive gauche conformational effect. Analysis of seven-membered rings containing endo and exo sulfur atoms

Dionne¹,

St‐Jacques²

1990

Can. J. Chem.

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The so-called repulsive gauche conformational effect associated with sulfur is investigated through a study of 3-methylthio-1,5-benzodioxepin (1) and 3-methylthio-1-benzoxepin (2), together with 3-fluoro-and 3-chloro-l,5-benzodithiepins (3 and 4), by I3C and 'H dynamic nuclear magnetic resonance methods. The results show that, while compounds 2 , 3 , and 4 exhibit a large amount of the C, conformation, the TB form predominates for compound 1. intramolecular stereoelectronic u-u* orbital interactions are analyzed, together with several other factors (steric, electrostatic, and solvation), to explain the observed conformational behaviour.Key words: gauche effect, seven-membered rings, 1,5-benzodithiepins, variable temperature NMR, orbital interactions.On a ttudit l'effet conforrnationnel gauche repulsif associt ii l'atome de soufre en examinant la 3-mCthylthio-l,5-benzodioxCpine (I), la 3-methylthio-1-benzoxtpine (2) ainsi que les 3-fluoro-et 3-chloro-l,5-benzodithitpines (3 et 4), par des mCthodes de rCsonance magnCtique nucliaire dynamique du I3C et du IH. Les rksultats dtmontrent que, alors que l'on dttecte la prisence de quantitts importantes de la conformation C, dans les composts 2 , 3 et 4, la forme TB prkdomine pour le composC 1. On a analyst les interactions stCrtoClectroniques intramolCculaires des orbitales u-u* ainsi que plusieurs autres facteurs (stCrique, tlectrostatique et de solvatation) afin de pouvoir expliquer le comportement conforrnationnel observt.Mots clks : effet gauche, cycles ii sept chainons, 1,5-benzodithitpines, RMN 2i temp6rature variable, interactions orbitales.[Traduit par la revue] Introduction Over the last few years, we have been interested in the mechanism of the gauche effect (1) and the underlying molecular interactions as revealed by the conformational analysis of some 3-substituted 1,5-benzodioxepins (2, 3) and 1-benzoxepins (4, 5). These results have shown that the seven-membered heterocycles can provide information complementary to analogous six-membered molecules because of the greater ring flexibility, giving rise to the twist boat (TB) form in addition to the axial chair (C,) and the equatorial chair (C,) conformations. Such studies unravelled the nature of the molecular orbital interaction involved. According to the rationalizations formulated earlier by Zefirov et al. (6) from studies of six-membered ring molecules, the conformational feature of the oxygen-containing seven-membered rings studied (2-5) was characteristic of attractive or negligible gauche effects. Our present aim is to analyze the repulsive gauche effect (6, 7) through the conformational study of seven-membered rings containing erzdo and exo sulfur atoms interacting with other heteroatoms such as in the series 1-6.

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Stereochemical studies—XX

Cited by 98 publications

References 73 publications

Convenient synthesis of 1,3-dithiolane-2-thiones: cyclic trithiocarbonates as conformational locks

Convenient synthesis of 1,3-dithiolane-2-thiones: cyclic trithiocarbonates as conformational locks

Vicinal ring H/H Coupling Constants of γ‐lactones containing two hydroxyl groups

Repulsive gauche conformational effect. Analysis of seven-membered rings containing endo and exo sulfur atoms

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