A Route to Carbasugar Analogues - Jonathan Clayden - The ...

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Chapter 2 – Dearomatising additions to aryl oxazolines 2.1.1 Summary of initial reactions Whilst the dearomatising addition of organolithiums was possible with three of the five oxazolines, the anti-diphenyl oxazoline is clearly best at promoting the dearomatisation. Failure of the cis oxazoline (109) after repeated attempts shows that the trans geometry is key, whilst the benzylic lithiation of the Meyers (104) and norephedrine (110) oxazolines indicate that the diphenyl system may be successful due to the mutual hindrance of C4 and C5. Mechanistically, the pseudo-C 2 nature of oxazolines 101 offers a very appealing rationale for the high levels of diastereoselectivity observed, although equally high diastereoselectivity was seen with anti-oxazolines 104 and 110. The other key component in the reaction is the DMPU co-solvent. DMPU has been used extensively in organolithium chemistry, largely as a less toxic substitute for HMPA. 65 It is a Lewis basic ligand for lithium, donating electron density through its oxygen lone pairs, purportedly making the organolithium more reactive through deaggregation, which is discussed at the end of the chapter. Oxazolines are traditionally used to direct ortho-metalation, and Scheme 2.3 shows that it might be possible to tune the reactivity of the aromatic ring, permitting functionalisation before dearomatisation. Addition of a range of Grignard reagents was also attempted to anisole 101b, but neither dearomatisation nor nucleophilic aromatic substitution were observed and only starting material was isolated. Finally, Table 2.1 shows that the six reactions in which dearomatisation occurred had similar opaque brown/green solutions such as that shown below. Scheme 2.6 – crystal structure and reaction solution of 102b 55
2.1 – A new reaction The next section will outline the study and optimisation of the stereoselective dearomatising addition, and the subsequent section looks at its application to a number of organolithiums, aromatic systems, and electrophiles. Section 2.4 will discuss the mechanistic implications of these results. Throughout these sections, the anti-diphenyl oxazoline discussed above will be abbreviated: Ph Ox* = O N Ph 56
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Dearomatising Addition of Organolit
Page 3 and 4: 2.3 Synthetic Scope 64 2.3.1 Organo
Page 5 and 6: Abstract Dearomatising Addition of
Page 7 and 8: The Author The Author graduated fro
Page 9 and 10: Abbreviations & Conventions Ac acet
Page 11 and 12: RDS rate determining step R f RC rt
Page 14 and 15: Chapter 1: Introduction Chapter 1 -
Page 16 and 17: Chapter 1: Introduction controlled
Page 18 and 19: Chapter 1: Introduction diastereome
Page 20 and 21: Chapter 1: Introduction combine mor
Page 22 and 23: Chapter 1: Introduction O Ar Cl TMP
Page 24 and 25: Chapter 1: Introduction conditions,
Page 26 and 27: Chapter 1: Introduction chiral oxaz
Page 28 and 29: Chapter 1: Introduction Again a lar
Page 30 and 31: Chapter 1: Introduction 34 Scheme 1
Page 32 and 33: Chapter 1: Introduction The amino a
Page 34 and 35: Chapter 1: Introduction It was envi
Page 36 and 37: Chapter 1: Introduction COR' i) ATP
Page 38 and 39: Chapter 1: Introduction O i) ATPH,
Page 40 and 41: Chapter 1: Introduction 1.4 Nucleop
Page 42 and 43: Chapter 1: Introduction Unlike the
Page 44 and 45: Chapter 1: Introduction Diene (-)-8
Page 46 and 47: Chapter 1: Introduction A scheme su
Page 48 and 49: Chapter 1: Introduction Cl R + 93 S
Page 50 and 51: Chapter 2 - Dearomatising additions
Page 92: Chapter 2 - Dearomatising additions
Page 95 and 96: 3.1 - Oxazoline synthesis 3.1.1.a H
Page 97 and 98: 3.1 - Oxazoline synthesis O Ar OH i
Page 99 and 100: 3.1 - Oxazoline synthesis 3.1.2 Gen
Page 101 and 102: 3.1 - Oxazoline synthesis mCPBA O N
Page 103 and 104: 3.1 - Oxazoline synthesis 3.1.4.b M
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3.1 - Oxazoline synthesis Ph Ph Ph
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3.2 - Oxazoline removal O N O OH 3N
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3.2 - Oxazoline removal O Me O N OM
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3.2 - Oxazoline removal However, th
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3.2 - Oxazoline removal 3.2.3 Reduc
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3.2 - Oxazoline removal Ph O N Ph P
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3.2 - Oxazoline removal 3.2.3.c Ami
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3.2 - Oxazoline removal Ph Ph Ph Ph
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3.2 - Oxazoline removal 3.2.5.b N-A
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3.2 - Oxazoline removal Ph Ph O N H
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3.2 - Oxazoline removal Ph Me Ph Me
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3.2 - Oxazoline removal 3.2.6 Deter
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Better, however, would be a method
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4.1 - Introduction HO OH OH HO OH O
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4.1 - Introduction (-)-Shikimic aci
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4.1 - Introduction followed by Flem
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4.2 - Carbasugar synthesis 4.2 Synt
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4.2 - Carbasugar synthesis stereoce
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4.2 - Carbasugar synthesis of the o
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4.2 - Carbasugar synthesis support
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4.2 - Carbasugar synthesis Ox* Ox*
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4.2 - Carbasugar synthesis OsO 4 (c
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4.2 - Carbasugar synthesis taken on
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4.2 - Carbasugar synthesis As well
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4.4 - Revised altrose synthesis 4.4
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4.4 - Revised altrose synthesis suf
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4.4 - Revised altrose synthesis ind
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4.5 - Mannose synthesis 4.5 Synthes
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4.5 - Mannose synthesis It is clear
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4.5 - Mannose synthesis considering
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4.5 - Mannose synthesis which would
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4.5 - Mannose synthesis One clear a
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4.5 - Mannose synthesis 4.5.2.b Epo
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4.5 - Mannose synthesis hydrolysis
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4.5 - Mannose synthesis The second
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4.6 - Summary 4.6 Summary & Future
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4.6 - Summary OH CDI, NH 2 OH.HCl,
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184
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References (37) Rawson, D. J.; Meye
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References (105) Gajewski, J. J.; B
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References (169) McCormick, J. P.;
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References 192
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Experimental section 254nm, dodecam
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Experimental section General Proced
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Experimental for chapter 2 Synthesi
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Experimental for chapter 2 (CDCl 3
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Experimental for chapter 2 3H, OMe
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Experimental for chapter 2 Ph), 139
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Experimental for chapter 2 H4), 5.2
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Experimental for chapter 2 108 R f
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Experimental for chapter 2 Synthesi
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Experimental for chapter 3.1 satura
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Experimental for chapter 3.1 Na 2 S
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Experimental for chapter 3.1 Synthe
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Experimental for chapter 3.1 128.9,
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Experimental for chapter 3.1 Microw
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Experimental for chapter 3.1 R f :
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Experimental for chapter 4.1 281 R
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Experimental for chapter 4.1 combin
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Experimental for chapter 4.1 3H, OB
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Experimental for chapter 4.2 (1S*,2
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Experimental for chapter 4.2 10.0,
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Experimental for chapter 4.2 cm 3 )
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Experimental for chapter 4.2 5.7 Re
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280
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Absolute structure parameter 1.3(11
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_diffrn_standards_interval_time ? _
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H13 H 0.8405 0.7136 -0.0889 0.026 U
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C4 C5 1.454(2) . ? C5 C6 1.324(2) .
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C24 C23 C22 120.0(2) . . ? C24 C23
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. Compound 102c Ph O N Ph Me 102c O
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_diffrn_standards_interval_time ? _
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H11 H 0.8924 0.9592 0.6829 0.022 Ui
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C2 H2 1.0000 . ? C3 C21 1.506(2) .
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C26 C21 C3 121.41(15) . . ? C23 C22
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c. Compound 213 Ph O N Ph Me OH 213
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_cell_volume 1080.9(4) _cell_formul
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_refine_ls_number_reflns 4736 _refi
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H25 H 0.7979 0.2335 0.3365 0.028 Ui
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C4 0.025(4) 0.019(4) 0.018(4) 0.001
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loop_ _geom_bond_atom_site_label_1
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C9 C4 C1 107.1(5) . . ? C10 C4 C1 1
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C36 C38 H38A 109.5 . . ? C36 C38 H3
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C29 C30 C36 C37 -90.4(7) . . . . ?
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The structure was solved by the dir
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_reflns_number_total 2447 _reflns_n
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C7 C 1.1671(4) 0.7629(7) 1.2254(4)
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C3 0.015(3) 0.016(3) 0.021(3) -0.00
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C21 H21A 0.9800 . ? C21 H21B 0.9800
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H21A C21 H21C 109.5 . . ? H21B C21
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