Impact of Silyl Ethyl Esters on the Rhodium(II)-Catalyzed Transformations of Donor/Acceptor Carbenes 公开

Cohen, Carolyn Michelle (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/5h73pw72d?locale=zh
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Abstract

Donor/acceptor carbenes are a privileged class of reagents that are capable of highly site-selective C-H bond functionalization when used in combination with transition metal catalysts. This ability to selectively functionalize a C-H bond has revolutionized organic synthesis in recent years. The transformations of a donor/acceptor carbene substituted with a trialkylsilyl moiety in the acceptor group are investigated. It was discovered that in the presence of the catalyst Rh2(TPA)4, triisopropylsilyl-substituted ethyl aryldiazoacetates undergo an intramolecular C-H insertion followed by decomposition of the beta-lactone intermediate, resulting in preferential formation of the more sterically hindered Z allylsilanes. In addition to this unexpected reactivity, the silyl substituted donor/acceptor carbenes are excellent substrates for cyclopropanation using Rh2(S-DOSP)4. This reaction has been applied to the synthesis of the triarylcyclopropane carboxylate ligand used in the catalyst Rh2(R-BTPCP)4.

Table of Contents

Table of Contents Page

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

Part 1: Reaction of a Silyl-Substituted Diazo Compound........................................11

Background: Allylsilanes.................................................................................12

Exploration of a New Allylsilane Reaction...........................................................14 Discussion....................................................................................................22

Part 2: Cyclopropanation.................................................................................25

Exploration of Ligand Synthesis........................................................................30 Conclusion....................................................................................................30

Experimental Data.........................................................................................32

Figures

1. Three classes of carbenes.............................................................................3

2. Structure of dirhodium(II) tetracarboxylate catalysts.........................................4

3. Dirhodium tetracarboxylate catalysts..............................................................5

4. Structure of Rh2(R-BTPCP)4...........................................................................7

5. Silyl substituted ethyl aryldiazoacetate............................................................8

6. Example cyclopropane natural product............................................................9

7. Structure of Rh2(TPA)4................................................................................16

Tables

1. Catalyst Optimization Study.........................................................................15

2. Initial Investigation of Reaction Scope............................................................17

3. Silyl Group Optimization..............................................................................18

4. Catalyst Optimization for Cyclopropanation.....................................................27

5. Exploration of Substrate Scope.....................................................................28

6. Substrate Scope with Optimized Conditions.....................................................29

Schemes

1. Synthesis of triarylcyclopropanecarboxylate ligand............................................8

2. Reaction of a silyl substituted diazo with Rh2(S-DOSP)4.....................................11

3. Control reaction for byproduct identification....................................................12

4. Exploration of Diazo Substrate Scope.............................................................20

5. Synthesis of Chiral Allylsilanes......................................................................21

6. General Synthesis of Diazo Compounds..........................................................22

7. Proposed Mechanism for Allylsilane Formation.................................................23

8. Control Reaction to Isolate Beta-lactone Intermediate.......................................23

9. Explanation of Observed Stereochemistry.......................................................25

10. Synthesis of Triarylcyclopropanecarboxylate..................................................30

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