Probing the Anomeric Effect. Trimethylsilyloxy and tert-Butoxy Substituents in 1,4-Dioxane Derivatives: Theory vs. Experiment1

Pinchas Aped, Yitzhak Apeloig, Avivakar Ellencweig, Benzion Fuchs, Israel Goldberg, Miriam Karni, Evgeny Tartakovsky

Research output: Contribution to journalArticlepeer-review

Abstract

A conformational analytical study of a series of trimethylsilyloxy- (TMSO) and tert-butoxy- (TBO) substituted 1,4-dioxanes was performed using NMR techniques. It was found that the TMSO and TBO groups (in contrast to MeO, AcO, and PhO substituents2) alleviate the anomeric effect. Arguments based on molecular mechanics (MM2-parametrized for the anomeric effect) and MO ab initio calculations of ROCOR/ (R = CH3, H; R' = SiH3) at various levels help rationalize this behavior, by isolating and identifying steric and electronic contributions. The electronic factors are (i) strong attractive nonbonded OSi…-0 interactions within the R-O-C-O-Si system, which reduce considerably the O-C-O-Si dihedral angle (down to 0°) and the energy of the “ag” (equatorial) form vs. the “g+g+” one and (ii) inductive electron donation by SiMe3(or CMe3) which lowers the electronegativity of TMSO (or TBO). Steric factors and (p →d)π bonding are negligible. A single-crystal X-ray analysis of 2,5-di-tert-butoxy-l,4-dioxane revealed structural data in line with all the above.

Original languageEnglish
Pages (from-to)1486-1495
Number of pages10
JournalJournal of the American Chemical Society
Volume109
Issue number5
DOIs
StatePublished - 1 Mar 1987

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