Cornell University
Library
Cornell UniversityLibrary

eCommons

Help
Log In(current)
  1. Home
  2. Cornell University Graduate School
  3. Cornell Theses and Dissertations
  4. STRUCTURE-SELECTIVITY PRINCIPLES UNDERLYING ALKYLATIONS OF OPPOLZER’S CAMPHORSULTAM ENOLATES

STRUCTURE-SELECTIVITY PRINCIPLES UNDERLYING ALKYLATIONS OF OPPOLZER’S CAMPHORSULTAM ENOLATES

File(s)
Lui_cornellgrad_0058F_13793.pdf (22.69 MB)
Permanent Link(s)
https://doi.org/10.7298/2pn4-cq46
https://hdl.handle.net/1813/114693
Collections
Cornell Theses and Dissertations
Author
Lui, Nathan Mancheun
Abstract

Camphorsultam-based enolates, referred to colloquially as Oppolzer enolates, are examined spectroscopically, crystallographically, kinetically, and computationally to ascertain the mechanism of alkylation and the origin of stereoselectivity. Solvent- and substrate-dependent structures of lithium Oppolzer enolates include tetramers for alkyl-substituted enolates in toluene, spirocyclic dimers for aryl-substituted enolates in toluene, substrate-independent symmetric dimers in tetrahydrofuran (THF) and THF/toluene mixtures, hexamethylphosphoramide-bridged (HMPA) trisolvated dimers at low HMPA concentrations, and disolvated monomers for the aryl-substituted enolates at elevated HMPA concentrations. Their sodium counterparts, however, reside as monomers in neat THF and THF/HMPA solutions and as dimers in toluene when solvated by N,N,N’N’-tetramethylethylenediamine (TMEDA) and N,N,N’,N’’N’’-pentamethyldiethylenediamine (PMDTA). Aided by density functional theory (DFT) extensive analyses of the stereochemistry of aggregation and solvation are included. Rate studies of allylation implicate analogous transition structures, namely an HMPA-solvated ion pair with a +Li(HMPA)4 or +Na(HMPA)5 counterion. Curious dependencies on toluene and THF are attributed to exclusively secondary-shell (medium) effects. Sparse reports detailing an analogous HMPA–free methylation are also explored, revealing a similar reaction pathway (via the THF-solvated E–//+Na(THF)6 ion pair). Aided by DFT calculations, a stereochemical model is presented in which the alkylating agent is guided to the exo–face of the camphor owing to stereoelectronic preferences imparted by the sultam sulfonyl moiety, rather than chelate directed endo–facial approach. Consequently, counter to decades of reasoning, the origins of stereoselectivity stem not from steric effects enforced by the chelation of the metal cation, but rather from chirality within the sultam ring imparted by the rigidity of the camphor skeletal core.

Description
913 pages
Date Issued
2023-08
Keywords
Camphorsultam
•
DFT calculations
•
Enolates
•
Kinetics
•
Mechanism
•
Organic chemistry
Committee Chair
Collum, David
Committee Member
Fors, Brett
Lin, Song
Degree Discipline
Chemistry and Chemical Biology
Degree Name
Ph. D., Chemistry and Chemical Biology
Degree Level
Doctor of Philosophy
Rights
Attribution-NoDerivatives 4.0 International
Rights URI
https://creativecommons.org/licenses/by-nd/4.0/
Type
dissertation or thesis
Link(s) to Catalog Record
https://newcatalog.library.cornell.edu/catalog/16219288

Site Statistics | Help

About eCommons | Policies | Terms of use | Contact Us

copyright © 2002-2026 Cornell University Library | Privacy | Web Accessibility Assistance