1976
DOI: 10.1002/9780470147184.ch4
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Multistep Conformational Interconversion Mechanisms

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Cited by 107 publications
(16 citation statements)
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“…The observed ring conformation is in agreement with that reported previously for the Ac 12 c residue [31]. This 12membered ring conformation, which is described as [3,3,3,3] according to Dale's nomenclature [46], was characterized in the crystal and electron diffraction studies of cyclododecane [47,48] and is the global minimum structure in the energy calculations of 12-membered rings [49,50]. A recent report on the cyclododecane conformation in crystal state also identified [3,3,3,3] as the sole conformer observed in crystalline state, so far [51].…”
Section: Resultssupporting
confidence: 91%
“…The observed ring conformation is in agreement with that reported previously for the Ac 12 c residue [31]. This 12membered ring conformation, which is described as [3,3,3,3] according to Dale's nomenclature [46], was characterized in the crystal and electron diffraction studies of cyclododecane [47,48] and is the global minimum structure in the energy calculations of 12-membered rings [49,50]. A recent report on the cyclododecane conformation in crystal state also identified [3,3,3,3] as the sole conformer observed in crystalline state, so far [51].…”
Section: Resultssupporting
confidence: 91%
“…I n the last few decades, internal rotation barriers have been widely studied experimentally due to their importance for the conformational analysis in the biochemical activity of drugs, enzymes, and proteins [1,2]. In this way, the interest in conformational analysis produced an expressive number of experimental data obtained for large number of molecules [3].…”
Section: Introductionmentioning
confidence: 99%
“…This is again in contrast to the ranking established from the diastereoselectivities of the epoxidations of 6-NHBn trans - 19 and 6-NBn 2 trans - 20 for the six-membered ring system: NHBn ≫ OH > NBn 2 . The presence of two relatively nonsterically demanding substituents within 7-NHBn trans - 55 likely results in a certain degree of conformational promiscuity (which is known for cycloheptene) with several possible reactive conformations, which satisfy the geometric requirements for efficient hydrogen-bonding to either the N -benzylammonium moiety or hydroxyl group, being accessible and so allowing the two hydrogen-bonding directed epoxidation processes to compete effectively with each other. The diastereoselectivities of epoxidation of the “parent” seven-membered ring substrates 7-NHBn 11 (85:15 dr; syn : anti ) and cyclohept-2-en-1-ol 3 (61:39 dr; syn : anti ) suggest modest directing proficiencies in this system; if the two are able to operate largely independently, a mixture of products slightly favoring epoxide 63 (resulting from direction from the N -benzylammonium moiety, the superior directing group) may be expected, as observed experimentally (56:44 dr).…”
Section: Resultsmentioning
confidence: 99%
“…In the substrates where the two established, individual directing group preferences would result in epoxidation being directed to the same face of the olefin, regardless of which group acts as the directing group (i.e., 5-NBn 2 cis - 40 , 6-NHBn cis - 24 , 6-NBn 2 cis - 25 , 7-NHBn cis - 53 , and 7-NBn 2 trans - 56 ), the observed diastereoselectivities are higher than those of the respective “parent” allylic alcohol 1 – 3 and ostensibly the same as those of the respective “parent” allylic amine 8 – 12 . Although in most cases the diastereoselectivities of the latter epoxidation process is at or beyond the limit of detection, the diastereoselectivity of epoxidation of 7-NHBn 11 (85:15 dr), resulting from direction by the ammonium moiety alone and falling well within the limits of detection, is not enhanced by the presence of the hydroxyl group within 7-NHBn cis - 53 (82:18 dr) and in this instance at least, the effect is unlikely due to a lack of conformational freedom given that seven-membered rings with nonsterically demanding substituents are involved . It may be that it is simply not feasible for both directing groups to form hydrogen-bonds to the peracid oxidant simultaneously.…”
Section: Resultsmentioning
confidence: 99%
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