Experimental and Theoretical Evidence of Through-Space Electrostatic Stabilization of the Incipient Oxocarbenium Ion by an Axially Oriented Electronegative Substituent during Glycopyranoside Acetolysis

Journal of Organic Chemistry

Volumn 62, Issue 22, 1997, Pages 7597-7604

  Miljković, Momčilo ^a   Yeagley, David ^a   Deslongchamps, Pierre ^b   Dory, Yves L ^b  

^a PENN STATE MILTON S HERSHEY MEDICAL CENTER   (United States)

^b UNIVERSITÉ DE SHERBROOKE   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000023645     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo970677d     Document Type: Article

References (23)

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2. For a good discussion of Stereoelectronic control of acetal hydrolysis and ALPH, see: (a) Deslongchamps, P. In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993; pp 26-54, (b) Deslongchamps, P. ; Dory, Y. L.; Li, S. Can. J. Chem. 1994, 72, 2021.
3. For a good discussion of Stereoelectronic control of acetal hydrolysis and ALPH, see: (a) Deslongchamps, P. In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993; pp 26-54, (b) Deslongchamps, P. ; Dory, Y. L.; Li, S. Can. J. Chem. 1994, 72, 2021.
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5. Sinnott, M. L. Adv. Pays. Org. Chem. 1988, 24, 113. See also; Sinott, M. L. In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993; pp 97-113.
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14. Both microfuge tubes and microvials were used for the various runs. Initially microfuge tubes were used for the acetolysis study, as well as for the determination of concentration curves because they were of the proper size and easy to vortex and the water, after the chloroform extraction, was much easier to remove than from glass microvials. When it was determined that they leached smaller oligomers into the acetone solution or into the chloroform extract hplc chromatograms (retention time >50 min)] glass microvials were used instead. However, further studies showed that (1) the contamination of the acetone or chloroform solution coming from polyethylene microfuge tubes can be completely eliminated if the microfuge tubes were kept at -78 °C and (2) it had no effect upon the acetolysis results (direct comparison of kinetic values in experiments eriments using polyethylene microfuge tubes at -78 °C or glass microvials at room temperature gave identical results).
15. Assuming that the 4-acetamido group of 3 and 6 could also be protonated, under the used reaction conditions, we have decided to use 100% molar excess of methanesulfonic acid for the acetolysis of these two substrates since we wanted to be sure that the molar concentration of methanesulfonic acid available for the protonation of the glycosidic oxygen atom is identical to the amount of methanesulfonic acid used in kinetic studies with four other glycopyranosides (1, 2, 4, and 5). However, if our assumption on protonation of the C4 acetamido group was wrong, then the determined acetolysis rates for these two glycopyranosides are possibly too high.
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22. ** level of theory yielding the following respective ZPE: 0.15976 and 0.15947 au (applied scale factor of 0.89). Due to the very small resulting energy correction (0.18 kcal/mol) and to system limitations, the Hessian matrices of the other struc- tures were not computed.
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