Synthesis of Highly Functionalized Pyrroles Using a Dirhodium Catalyst Open Access

Green, Samantha Alyson (2013)

Permanent URL: https://etd.library.emory.edu/concern/etds/37720d16z?locale=en
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Abstract

Pyrroles are common structural motifs in natural compounds, which, in recent years, have called for an increased demand of new methods for their synthesis. The conversion of furan to highly functionalized pyrroles was investigated using a dirhodium catalyst. It was found that in the presence of an N-sulfonyltriazoles, a formal [3+2] cycloaddition occurred to produced bicyclic hemiaminals which ring opened, resulting in pyrrole product. This study focused primarily on expanding the scope of this reaction in terms of variation of the N-sulfonyl protecting group and substituents on the triazole compound. In comparison to other synthetic methods, this synthesis utilizes mild reaction conditions and inexpensive, shelf-stable starting materials.

Table of Contents

Table of Contents Page

Introduction...................................................1

New Approach to Pyrrole Synthesis....................11

Lewis Acid Exploration.....................................14

Heterocycle Exploration...................................16

Furan Exploration...........................................19

Triazole Synthesis..........................................21

Discussion/Conclusion.....................................26

Experimental Data..........................................31

Figure Page

1. Structure of Rh2(S-DOSP)4...........................11

Tables

1. Catalyst and Solvent Screening.....................12

2. Exploration of Chiral Catalysts......................14

3. Lewis Acid Screening..................................15

4. Heterocycle Scope Exploration......................17

5. 2,5-Disubstituted Furan Scope.......................20

6. Ethanesulfonyl Substrate Scope.....................22

7. Triazole Substrate Scope..............................25

Schemes

1. Pd-Catalyzed Pyrrole Formation....................................................................3

2. 4-pi-electrocyclization synthesis of pyrroles.....................................................4

3. Copper and Rhodium catalyzed formation of disubstituted indolizines....................7

4. Ring-opened diene product through zwitterionic intermediate...............................9

5. Mechanism of 8-oxabicyclo[3.2.1]octadiene formation........................................10

6. Proposed mechanism for pyrrole formation.......................................................26

7. Proposed cyclopropanation mechanism for pyrrole formation...............................27

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