i. lewis base-catalyzed aldol reaction in the total synthesis of erythronolide b ii. efforts towards the

186 Pages·2011·1.01 MB·English

I. LEWIS BASE-CATALYZED ALDOL REACTION IN THE TOTAL SYNTHESIS OF
ERYTHRONOLIDE B
II. EFFORTS TOWARDS THE TOTAL SYNTHESIS OF AMPHIDINOLIDE H

by
Dezhi Fu
Bachelor of Science, Lanzhou University, 2002
Master of Science, Brown University, 2006

Submitted to the Graduate Faculty of
Arts and Sciences in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy

University of Pittsburgh
2011
UNIVERSITY OF PITTSBURGH
FACULTY OF ARTS AND SCIENCES

This dissertation was presented

by

Dezhi Fu

It was defended on
April 8,2011
and approved by

Theodore Cohen, Professor, Department of Chemistry
Craig S. Wilcox, Professor, Department of Chemistry
Billy W. Day, Professor, Department of Pharmaceutical Sciences
Dissertation Advisor: Scott G. Nelson, Professor, Department of Chemistry

ii
Copyright © by Dezhi Fu
2011
iii
I. LEWIS BASE-CATALYZED ALDOL REACTION IN THE TOTAL SYNTHESIS
OF ERYTHRONOLIDE B
II. EFFORTS TOWARDS THE TOTAL SYNTHESIS OF AMPHIDINOLIDE H

Dezhi Fu, PhD
University of Pittsburgh, 2011

Lewis base (trimethylsilylquinine and trimethylsilylquinidine) catalyzed acyl halide-aldehyde
cyclocondensation (AAC) reactions have been developed to prepare synthetically important
bispropionate units previously by the Nelson group. A new Lewis base-catalyzed
diastereoselective Mukaiyama aldol reaction has extended this bispropionate unit preparation
methodology to all-syn bispropionates which widely occurred in polypropionate natural products.
By using phenoxides as Lewis base catalysts, enol silanes were activated and underwent a Felkin
attack on an aldehyde through an antiperiplanar transition state to generate all-syn bispropionate
product in high yields and excellent diastereoselectivities.
Me Me
Me OAr ArO Me
Si Si
OTMS O Me Me O MeH O OSi OTBS
Me ArO– Me O N R
N N N H R
L Me Me
Me
OTBS
Si = silyl protecting group R =
L
R
All-syn bispropionate prepared from the Lewis base-catalyzed diastereoselective
Mukaiyama aldol reaction has been untilized in natural product synthesis of erythronolide B
establishing “syn,syn,syn” stereochemical relationships from C -C .
2 5
iv
O
Me Me
8
Me
Me 7
O OH OH
OH
OH
2 4 Me 13 Me 5
N 1 3 5 OH
O 4
Me Me Me
O OH
2
"syn, syn, syn" Bispropionate Synthon Me
Erythronolide B
Studies towards the total synthesis of the cytotoxic marine macrolide amphidinolide H (89)
have been disclosed. By exploiting AAC methodology, several key stereochemical relationships
present in major fragments 198 and 199 were established. A highly enantioselective synthesis of
methyl ketone 200 was realized from commercially available (S)-(−)-glycidol. Iodide 198 was
coupled with boronic ester 199 via an efficient Suzuki reaction to form a C -C fragment.
7 20

Aldol coupling
Me OH O
Me OH O
Me OH
18 Me OH
22
14 Me Suzuki
HO Me
HO
Me 196
Me OH Me
11 6 OH
+
O
OH
O 1 CHO
Julia olefination O Macrolactonization O SO2Ph Me
OTMSE
Amphidinolide H (89) Me O
Me 197 O
H
O C H OMe-p
198 6 4
I
O
+ Me
B(Pin)
2
Me
O
Me
OBn
OTBS 200
OTES
O
199

v
TABLE OF CONTENTS
1.0 LEWIS BASE-CATALYZED DIASTEREOSELECTIVE MUKAIYAMA
ALDOL REACTION FOR ALL-SYN BISPROPIONATE UNITS........................................1
1.1 INTRODUCTION.......................................................................................................1
1.1.1 Aldol Reaction...................................................................................................1
1.1.2 Synthesis of Polyketide and Polypropionate Units........................................3
1.1.3 Lewis Base-Catalyzed Mukaiyama Aldol Reaction.......................................8
1.2 LEWIS BASE-CATALYZED DIASTEREOSELECTIVE MUKAIYAMA
ALDOL REACTION FOR ALL-SYN BISPROPIONATE UNITS..............................13
1.2.1 Bispropionate Units in the Total Synthesis of Erythronolide B.................13
1.2.2 Design of Enol Silane for Mukaiyama Aldol Reaction................................15
1.2.3 BF -Mediated Mukaiyama Aldol Reaction..................................................17
3
1.2.4 Lewis Base-Catalyzed Mukaiyama Aldol Reaction.....................................20
1.3 CONCLUSION..........................................................................................................36
1.4 EXPERIMENTALS..................................................................................................38
2.0 EFFORTS TOWARDS THE TOTAL SYNTHESIS OF AMPHIDINOLIDE H 54
2.1 INTRODUCTION.....................................................................................................54
2.1.1 The Amphidinolides.......................................................................................54
2.1.1.1 Isolation................................................................................................54
vi
2.1.1.2 Structural Features and Biological Activity.....................................55
2.1.2 Previous Approaches to the Total Synthesis of Amphidinolide H1...........57
2.1.3 Application of AAC Reaction Technology in the Total Synthesis of
Amphidinolide H1......................................................................................................66
2.2 EFFORTS TOWARDS THE TOTAL SYNTHESIS OF AMPHIDINOLIDE H69
2.2.1 The Retrosynthesis of Amphidinolide H1....................................................69
2.2.2 The First Generation of Synthesis of the C –C Fragment......................70
14 26
2.2.2.1 Model Study for preparing Fragment C –C .................................70
14 26
2.2.2.2 Synthesis of the C -C Fragment 148..............................................72
14 21
2.2.2.3 Synthesis of the C -C Model Fragment.........................................74
22 26
2.2.2.4 Model Study of Aldol Coupling of C -C Fragment With C -C 76
14 21 22 26
2.2.3 The Second Generation of Synthesis of the C –C Fragment..................77
14 26
2.2.3.1 The Retrosynthesis of the C –C Fragment....................................77
14 26
2.2.3.2 The Synthesis of Fragment 168..........................................................78
2.2.3.3 The Synthesis of Fragment 169..........................................................80
2.2.3.4 Dithiane Addition Trials.....................................................................85
2.2.4 Revised Synthesis of Amphidinolide H1.......................................................87
2.2.4.1 The Revised Retrosynthesis of Amphidinolide H1...........................87
2.2.4.2 Synthesis of the C -C Fragment 199 100..........................................88
7 13
2.2.4.3 Synthesis of the C -C Fragment 211..............................................90
14 18
2.2.4.4 Synthesis of the C -C Fragment 200..............................................92
19 26
2.2.4.5 Fragments Coupling............................................................................93
2.3 CONCLUSIONS........................................................................................................95
vii
2.4 EXPERIMENTALS..................................................................................................96
APPENDIX................................................................................................................................112
BIBLIOGRAPHY.....................................................................................................................161
viii
LIST OF TABLES
Table 1. Initial trial of Lewis base for Mukaiyama aldol reaction................................................22
Table 2. Screen of counter ions of theLewis base for Mukaiyama aldol reaction.......................23
Table 3. Lithium phenoxide-catalyzed Mukaiyama aldol reaction..............................................25
Table 4. Screen of substituents on phenoxide...............................................................................27
Table 5. Solvents screened for tetrabutylammonium phenoxide-catalyzed Mukaiyama aldol
reaction..........................................................................................................................................29
Table 6. Temperature screen of tetrabutylammonium phenoxide-catalyzed Mukaiyama aldol
reaction..........................................................................................................................................30
Table 7. Comparison of Lewis base-catalyzed Mukaiyama aldol reaction and Lewis acid-
mediated Mukaiyama aldol reaction for all-syn bispropionate synthesis.....................................32
Table 8. Comparison of enol silanes for electronic properties.....................................................34
Table 9. Enol silane comparisons.................................................................................................35
Table 10. Scope of enol silanes.....................................................................................................36
Table 11. Crystal data and structure refinement for 84..............................................................113
Table 12. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x
103) for 81...................................................................................................................................114
Table 13. Bond lengths [Å] and angles [°] for 84.......................................................................115
Table 14. Anisotropic displacement parameters (Å2x 103) for 84............................................119
ix
Table 15. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for
84.................................................................................................................................................120
Table 16. Crystal data and structure refinement for 68..............................................................121
Table 17. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x
103) for 68...................................................................................................................................123
Table 18. lengths [Å] and angles [°] for 68................................................................................124
Table 19. Anisotropic displacement parameters (Å2x 103) for 68............................................128
Table 20. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for
68.................................................................................................................................................129
Table 21. Crystal data and structure refinement for 81..............................................................130
Table 22. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x
103) for 81...................................................................................................................................132
Table 23. Bond lengths [Å] and angles [°] for 81.......................................................................133
Table 24. Anisotropic displacement parameters (Å2x 103) for 81............................................137
Table 25. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for
81.................................................................................................................................................138
Table 26. Crystal data and structure refinement for 78..............................................................139
Table 27. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x
103)for 78....................................................................................................................................141
Table 28. Bond lengths [Å] and angles [°] for 78.......................................................................143
Table 29. Anisotropic displacement parameters (Å2x 103) for 78............................................150
x