Enantioselective, Lewis base-catalyzed transformations: I. Polyene sulfenocyclization (preparative and mechanistic aspects) II. Sulfenofunctionalization of alkenyl boronates enabled by 1,2-boronate migration

This thesis covers two independent projects which are united under the umbrella of Lewis base catalysis. Following an overview of the key principles behind Lewis base catalysis and how it is used to enhance the electrophilicity of Lewis acids (Chapter 1), the bulk of this thesis will focus on the development of a catalytic, enantioselective sulfenocyclization of polyenes (Chapter 2). Sulfenyl group transfer from a highly reactive, cationic, Lewis acid-base adduct to an unactivated alkene generates a cyclic thiiranium ion, which serves as the initiating event for a highly stereoselective polyene cyclization that is terminated by arenes or phenols. This reaction was enabled by the identification of hexafluoroisopropyl alcohol (HFIP) as a superior solvent which dramatically improves site selectivity of thiiranium ion generation. A broad substrate scope is demonstrated, and the tricyclic products are isolated in good yield and enantioselectivity. Furthermore, a number of functional group interconversions (FGIs) of the resulting thioether moiety are demonstrated. This method is employed for the concise, enantioselective syntheses of the natural products (+)-ferruginol and (+)-hinokiol. Additionally, investigations into the sulfenocyclization of trienes to form even more complex products are disclosed. Preliminary mechanistic experiments to elucidate the rate-determining step of the catalytic cycle and the order in each reaction component were also performed. Chapter 3 of this thesis will cover the development of a Lewis base-catalyzed, enantioselective carbosulfenylation of alkenylboronate complexes which is enabled by a 1,2-boronate migration. The generation of “iranium” ions from alkenylboronates triggers a diastereospecific, ring-opening migration of an alkyl or aryl group to form 1,2-difunctionalized organoboron compounds. This strategy was employed together with Lewis base-catalyzed, enantioselective sulfenyl group transfer to ultimately afford chiral, non-racemic alkylboronic esters in generally high yield, high enantioselectivity, and perfect diastereospecificity. The products of the transformation are useful synthetic intermediates, and a number of useful FGIs are demonstrated.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Robb, Kevin Allen

Contributors dc:contributor

• Smith, Patriann
• Trent, William
• Brown, Ruth N.
• Zimmerman, Steven C.
• Stovall, David

• Lewis base catalysis
• polyene cyclization
• alkenylboronates
• enantioselective catalysis
• olefin sulfenofunctionalization

Statement dc:rights

• Copyright 2019 Kevin A. Robb

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/105593

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/105593