CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

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conversions occurring under the chosen conditions. Even if this condition is met, the problems associated with this are far from being fully solved. Frequently a substrate may have multiple functional groups that react with the reagents used. Hence, the development of efficient catalytic system for selective organic transformation is currently one of the challenging tasks in synthetic organic chemistry. 2 This is generally achieved using metal complexes and/ or biocatalysts that ensures higher degree of selectivity, better efficacy, and thus, fulfills the criteria of ideal organic synthesis. Of late, there is a paradigm shift of the perspectives of organic synthesis. For example, the stereoisomers of a compound are now considered as separate molecular entities with specific properties. Hence there is a great demand for developing highly stereoselective asymmetric routes for the synthesis of the target compounds. Thus, selectivity has become the keyword of modern organic synthesis as it provides solutions to the above problems, besides furnishing the so-called “tailored molecules” in the most efficient way. Given the importance of stereoselectivity in organic synthesis, a brief account of stereoselective asymmetric synthesis is provided in this chapter. The present work was mainly focused on the development of operationally simple and practically viable asymmetric strategies that include some metal-mediated routes and non-conventional protocols, and their possible application to the homologation of (D)-mannitol derived (R) - 2,3-cyclohexylideneglyceraldehyde (1). 3 O O CHO Fig. I.1.1. Structure of (R) -2,3-cyclohexylideneglyceraldehyde (1) 2
II. .22 IINTRODUCTIION TO CHIIRALIITY AND ASSYMMETRIIC SSYNTHESSIISS The demand for chiral compounds, often as single enantiomers, has escalated sharply in recent years, driven particularly not only by the demands of the pharmaceutical industry, but also by other applications, including agricultural chemicals, flavors, fragrances, and materials, especially in chiral polymers and liquid crystals. Two-thirds of prescription drugs are chiral, with the majority of new chiral drugs being single enantiomers. This widespread demand for enantiomerically pure chiral compounds has stimulated intensive research to develop improved methods for synthesizing such compounds. In addition to this, enantiomerically pure compounds are of most importance because of the fact that two enantiomers are considered different when screened for pharmacological activity, 4 and in some cases, it could mean between life and death if the manufactured drug is not enantiomerically pure. There are many examples of pharmaceutical drugs, 5 agrochemicals 6 and other chemicals, where the desired biological property is very much related to the absolute configuration. Some representative examples are shown in Fig. I.2.1. The recognition events in biology and the action of drugs that intervene in these events almost always involve the molecular recognition of a biologically active molecule by a chiral non-racemic receptor structure. The two enantiomers of a drug molecule cannot be expected to bind equally well to the receptor and so should cause different biological responses. Thus, only one enantiomer of the drugs is often endowed with the desired biological activity, while the other enantiomer is inactive or possesses a different activity and may cause toxic side effects. For example, in the series of eight possible stereoisomers of dibromovinyl-2,2-dimethylcyclopropane carboxylic esters (pyrethroid insecticides) the 3
Page 1: ASYMMETRIC STRATEGIES FOR THE SYNTH
Page 6 and 7: ACKNOWLEDGEMENTS First of all, I wa
Page 8 and 9: CONTENTS SYNOPSIS LIST OF FIGURES L
Page 10: SYNOPSIS
Page 13 and 14: models (e. g. Cram’s model, Felki
Page 15 and 16: 4 1d 4-(CH 3 ) 2 CH-C 6 H 4 1 : 1.5
Page 17 and 18: 14. 1n C 6 H 5 CO C 6 H 5 2n 8 77 1
Page 19 and 20: imetallic systems. In all the cases
Page 21 and 22: For the benzylation reaction, the c
Page 23 and 24: O O 3 CHO i O O + OH 13a O O OH O O
Page 25 and 26: 10 3.5 Ga (2.5) THF KI+LiCl 10 55 5
Page 27 and 28: multidrug-resistant (MDR) cancer ce
Page 29 and 30: directly afforded the furanose, whi
Page 31 and 32: References 1. Stephenson, G. R. Adv
Page 33 and 34: LIST OF FIGURES
Page 35 and 36: II.3.13 III.1.1 III.1.2 III.1.3 III
Page 37 and 38: IV.5.2 IV.5.3 IV.5.4 IV.5.5 1 H NMR
Page 39 and 40: Table Title Page No. II.3.1 II.3.2
Page 41: II. .11 PPREAMBLE Demand for specia
Page 45 and 46: The most dramatic example in this a
Page 47 and 48: H H 2 N OH COOH i PhH 2 CO O H N H
Page 49 and 50: Methods of Asymmetric Synthesis: 15
Page 51 and 52: O O O O i, ii iii iv HO HO N N OH O
Page 53 and 54: Models for Asymmetric Synthesis. 21
Page 55 and 56: If a strongly electronegative group
Page 57 and 58: enantiomeric products are formed at
Page 59 and 60: vi) The balance between chiral auxi
Page 61 and 62: IIII. .11 IINTRODUCTIION TO CHIIRAL
Page 63 and 64: Scheme II.1.2 However, availability
Page 65 and 66: Prof. R. Noyori received the Nobel
Page 67 and 68: Apart from the cinchona alkaloids,
Page 69 and 70: ligand, it assumes a tetrahedral co
Page 71 and 72: Marshall. 53 More recently, Barbero
Page 73 and 74: Various protocols have been develop
Page 75 and 76: In the absence of a sterically-bulk
Page 77 and 78: IIII. .33. . PPRESSENT WORK It is w
Page 79 and 80: [pyridinium][Sn 2 Cl 5 ] etc. can b
Page 81 and 82: RCHO 59a-j i R OH 60a-j (i) Allyl b
Page 83 and 84: Fig. II.3.2. 1 H NMR spectrum of 60
Page 85 and 86: in [bmim][BF 4 ] using sub-stoichio
Page 87 and 88: The reaction in THF was also follow
Page 89 and 90: The integration of the signal at δ
Page 91 and 92: The standard reduction potential of
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It has also been reported, 83a,b th
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IIII. .33. .33 Gaal lliuum meeddi i
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5 3.0 5.0 THF LiCl+KI c 14 d 71 6 1
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3 59d 4-(CH 3 ) 2 CH-C 6 H 4 H 60d
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Fig. II.3.8. 13 C NMR spectrum of 6
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Fig. II.3.10. 13 C NMR spectrum of
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fragmentation peak at m/z 138 (19%)
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Fig. II.3.13. 13 C NMR spectrum of
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active catalyst, as suggested for t
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1-(4-Bromophenyl)-but-3-en-1-ol 59b
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1H), 7.90-7.93 (m, 1H); 13 C NMR:
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662, 980, 1079, 1332, 1374 cm -1 .
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IIIIII. .11 DIIASSTEREOSSELECTIIVE
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cyclohexylideneglyceraldehyde (1) 3
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mixture of Zn dust, allyl or γ-sub
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Fig. III.1.2. 13 C NMR spectrum of
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Reaction with crotyl bromide: In ca
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Fig. III.1.5. 1 H NMR spectrum of 6
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The formation of the 2,3-anti addit
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To establish the C-4 configuration
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Allylation with (E) and (Z)-1-bromo
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(i) Zn, aqueous satd. NH 4 Cl, THF,
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Fig. III.1.12. 1 H NMR spectrum of
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Allylation with 1-Bromo-4-(tert)-bu
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fast and gave a significantly bette
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espectively) due to the cyclohexyli
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was treated with excess amount of b
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Fig. III.1.20. 1 H NMR spectrum of
Page 151 and 152:
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stereochemistry of allylation of β
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of the products were modest (48-62%
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6 1.2 In (2.0) H 2 O LiCl+ KI 14 72
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are consistent with our previous re
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III.3 EXPERIMENTAL SECTION: General
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(2R,3R)-1,2-Cyclohexylidenedioxy-5-
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for an additional 2 h, gradually br
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(m, 2H), 5.82-5.98 (m, 1H), 7.25-7.
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31.6, 32.2, 63.4, 128.8, 133.0. Ana
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23 (2R,3S,4R)-1,2-Cyclohexylidenedi
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(2R,3S,4S)-1,2-Cyclohexylidenedioxy
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(m, 1H), 3.50-4.02 (m, 5H), 4.10-4.
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and dried. Removal of solvent in va
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ine, and dried. Solvent removal und
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IIV. .11 SSYNTHESSIISS OFF ENANTIIO
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Scheme IV.1.1 The same group also d
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IV.1.3: Present work Although sever
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O O C 6 H 13 i O C 6 H 13 ii OH C 6
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Fig. IV.1.4. 1 H NMR spectrum of 10
Page 191 and 192:
the unit-C contribute positively to
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tartrate, Ti(O-i-Pr) 4 , CH 2 Cl 2
Page 195 and 196:
Based on this hypothesis, the alcoh
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OR 3 O R 1 R 2 NaBH 4 H H R 1 R 1 +
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(OH). Oxidative cleavage of its α-
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
IIV. .33: : SSYNTHESSIISS OFF 33' '
Page 207 and 208:
For the actual synthesis, (Scheme I
Page 209 and 210:
Page 211 and 212:
IV.4: SSYNTHESSIISS OFF 22( (SS) )-
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(i) PhCHO, triethyl orthoformate, M
Page 215 and 216:
O N 3 II Ph HO OH b1 N 3 Ph O O Ben
Page 217 and 218:
Page 219 and 220:
Thus, easily accessible 1 has been
Page 221 and 222:
167 and subsequent reduction gave 1
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from the appearance of 13 C NMR pea
Page 225 and 226:
Page 227 and 228:
IV.6 EXPERIMENTAL SECTION (2R,3S,4R
Page 229 and 230:
As described earlier, compound 108
Page 231 and 232:
19.5, 23.8, 23.9, 25.1, 26.9, 34.6,
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74.2, 74.4, 110.1, 116.7, 127.6, 12
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mmol) in MeOH (10 mL), work up, fol
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7.51 (m, 3H), 7.92-8.08 (m, 2H); 13
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subsequent isolation afforded rotam
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4.18 (t, J = 3.4 Hz, 1H), 4.75-4.84
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-4.21 (c 1.2, CHCl 3 ); IR: 3466, 1
Page 245 and 246:
(3R)- 3,4-O-Cyclohexylidene-2-oxo-1
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Water and EtOAc was added to the mi
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24 179. Yield: 1.49 g (77.5%); colo
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24 furnished pure 183. Yield: 0.37
Page 253 and 254:
1. Wender, P. A. Chem. Rev. 1996, 9
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17. Hanessian, S.; Maji, D. K.; Gov
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32. For some selective references s
Page 259 and 260:
43. (a) Cleare, M. J.; Hydes, P. C.
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54. Barbero, A.; Pulido, F. J.; Rin
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2008, 1681. (d) Fargeas, V.; Zammat
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72. Karodia, N.; Guise, S.; Newland
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Kaminski, J.; Millhauser, G.; Ortiz
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Böhm, V. P. W.; Reisinger, C. J. O
Page 271 and 272:
119. Wender, P. A.; Holt, D. A.; Si
Page 273 and 274:
140. (a) Chemler, S. R.; Roush, W.
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Lett. 1996, 107, 53. (c) Smith, C.
Page 277 and 278:
158. Mitsuya, H.; Weinhold, K. J.;
Page 279 and 280:
L.; Zugay, J. A. J. Med. Chem. 1993
Page 281 and 282:
1. Goswami, D.; Chattopadhyay, A.;
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