CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

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higher in [bmim][Br]. The results are tabulated in Table III.2.3. In almost all the cases the anti,anti isomer 79c was formed as the major diastereomer. Table III.2.3. Reaction course of 78a with 1 a Entr y 78a (equiv.) Metal (equiv.) Solvent Additive Time (h) Yield Product ratio c (%) b 79a:79b:79c 1 4 In (2.5) H 2 O -- 5 58 3.1:35.0:61.9 2 3.5 In (2.5) THF KI+LiCl 16 NR e -- 3 1.2 In (1.0) [bmim][Br] -- 6 78 11.0:42.0:37.0 4. 4 Ga (2.5) H 2 O KI+LiCl d 16 NR e -- 5 3.5 Ga (2.5) THF KI+LiCl d 16 NR e -- 6 1.2 Ga (1.0) [bmim][Br] -- 7 79 3.4:44.5:52.1 7. 3.5 Bi (2.5) H 2 O KI+LiCl 20 65 7.2:31.8:61.0 8 3.0 Bi (2.0) THF KI+LiCl 12 43 12.0:22.0:66.0 9 1.5 Bi (1.2) [bmim][Br] -- -- 72 5.0:35.4:59.6 a The reactions were carried out at 2 mmol scale. b The yields refer to those of isolated pure isomers. c The isomeric ratios were determined from the isolated yields. d The reactions were carried out under ultrasonication. e NR: no reaction. Mechanism of the reaction. Although an α- or a β-oxygenation in carbonyl compounds is reported to be most effective for chelation to the metals, 136 the aldehyde 1 gave predominantly 4,5-anti-diols with both In and Ga. This indicated that due to the bulky cyclohexanedioxy group in 1 precluded any chelation control in the reaction. The results 116
are consistent with our previous results with the bimetallic protocols and can be rationalized by the Felkin-Anh model. The 3,4-diastereoselectivity of the reaction involving γ-substituted (Me or C 6 H 13 ) allylic metal reagents and aldehydes may, in principle, involve a series of cyclic transition states, wherein the allylmetal reagent coordinates intramolecularly to the oxygen atom of the carbonyl group (Fig. III.2.1). Formation of TS1 and/or TS2 leads to the syn-adduct, while the anti-product is obtained from TS3 and/or TS4. Given that no other intramolecular chelation operates for this reaction, the transition state TS3 leading to the 3,4-anti-adduct is most favourable from the steric point of view, because both R and R' (cyclohexylidene) groups adopt equatorial positions in it, and the allylic-metal exists as the E-form, irrespective of the geometry of the starting bromide. 137 The stereoselectivity is considered to be the outcome of the orientation of R group. These explain the preferential formation of 69c in the Ga-mediated crotylation of 1. On the other hand, the preferential formation of 3,4-syn product 69b in the Bi-mediated crotylation reaction suggested an extensive conversion of the initially formed E-allylbismuth species to the corresponding Z- isomer. However, the effect of the metal and solvent on the diastereoselectivity of the reactivity is unclear. A large number of other factors such as nature of the metal, 138 counterion-dependence, aggregation state of the nucleophiles 139 may be involved in dictating this diastereoselectivity and any more detailed rationalization would be, at best, speculative. 117
Page 1:
ASYMMETRIC STRATEGIES FOR THE SYNTH
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ACKNOWLEDGEMENTS First of all, I wa
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CONTENTS SYNOPSIS LIST OF FIGURES L
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SYNOPSIS
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models (e. g. Cram’s model, Felki
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4 1d 4-(CH 3 ) 2 CH-C 6 H 4 1 : 1.5
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14. 1n C 6 H 5 CO C 6 H 5 2n 8 77 1
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imetallic systems. In all the cases
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For the benzylation reaction, the c
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O O 3 CHO i O O + OH 13a O O OH O O
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10 3.5 Ga (2.5) THF KI+LiCl 10 55 5
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multidrug-resistant (MDR) cancer ce
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directly afforded the furanose, whi
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References 1. Stephenson, G. R. Adv
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LIST OF FIGURES
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II.3.13 III.1.1 III.1.2 III.1.3 III
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IV.5.2 IV.5.3 IV.5.4 IV.5.5 1 H NMR
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Table Title Page No. II.3.1 II.3.2
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II. .11 PPREAMBLE Demand for specia
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II. .22 IINTRODUCTIION TO CHIIRALII
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The most dramatic example in this a
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H H 2 N OH COOH i PhH 2 CO O H N H
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Methods of Asymmetric Synthesis: 15
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O O O O i, ii iii iv HO HO N N OH O
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Models for Asymmetric Synthesis. 21
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If a strongly electronegative group
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enantiomeric products are formed at
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vi) The balance between chiral auxi
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IIII. .11 IINTRODUCTIION TO CHIIRAL
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Scheme II.1.2 However, availability
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Prof. R. Noyori received the Nobel
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Apart from the cinchona alkaloids,
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ligand, it assumes a tetrahedral co
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Marshall. 53 More recently, Barbero
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Various protocols have been develop
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In the absence of a sterically-bulk
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IIII. .33. . PPRESSENT WORK It is w
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[pyridinium][Sn 2 Cl 5 ] etc. can b
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RCHO 59a-j i R OH 60a-j (i) Allyl b
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Fig. II.3.2. 1 H NMR spectrum of 60
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in [bmim][BF 4 ] using sub-stoichio
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The reaction in THF was also follow
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The integration of the signal at δ
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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%)
Page 107 and 108: Fig. II.3.13. 13 C NMR spectrum of
Page 109 and 110: active catalyst, as suggested for t
Page 111 and 112: 1-(4-Bromophenyl)-but-3-en-1-ol 59b
Page 113 and 114: 1H), 7.90-7.93 (m, 1H); 13 C NMR:
Page 115 and 116: 662, 980, 1079, 1332, 1374 cm -1 .
Page 117 and 118: IIIIII. .11 DIIASSTEREOSSELECTIIVE
Page 119 and 120: cyclohexylideneglyceraldehyde (1) 3
Page 121 and 122: mixture of Zn dust, allyl or γ-sub
Page 123 and 124: Fig. III.1.2. 13 C NMR spectrum of
Page 125 and 126: Reaction with crotyl bromide: In ca
Page 127 and 128: Fig. III.1.5. 1 H NMR spectrum of 6
Page 129 and 130: The formation of the 2,3-anti addit
Page 131 and 132: To establish the C-4 configuration
Page 133 and 134: Allylation with (E) and (Z)-1-bromo
Page 135 and 136: (i) Zn, aqueous satd. NH 4 Cl, THF,
Page 137 and 138: Fig. III.1.12. 1 H NMR spectrum of
Page 139 and 140: Allylation with 1-Bromo-4-(tert)-bu
Page 141 and 142: fast and gave a significantly bette
Page 143 and 144: espectively) due to the cyclohexyli
Page 147 and 148: was treated with excess amount of b
Page 149 and 150: Fig. III.1.20. 1 H NMR spectrum of
Page 153 and 154: stereochemistry of allylation of β
Page 155 and 156: of the products were modest (48-62%
Page 157: 6 1.2 In (2.0) H 2 O LiCl+ KI 14 72
Page 161 and 162: III.3 EXPERIMENTAL SECTION: General
Page 163 and 164: (2R,3R)-1,2-Cyclohexylidenedioxy-5-
Page 165 and 166: for an additional 2 h, gradually br
Page 167 and 168: (m, 2H), 5.82-5.98 (m, 1H), 7.25-7.
Page 169 and 170: 31.6, 32.2, 63.4, 128.8, 133.0. Ana
Page 171 and 172: 23 (2R,3S,4R)-1,2-Cyclohexylidenedi
Page 173 and 174: (2R,3S,4S)-1,2-Cyclohexylidenedioxy
Page 175 and 176: (m, 1H), 3.50-4.02 (m, 5H), 4.10-4.
Page 177 and 178: and dried. Removal of solvent in va
Page 179 and 180: ine, and dried. Solvent removal und
Page 181 and 182: IIV. .11 SSYNTHESSIISS OFF ENANTIIO
Page 183 and 184: Scheme IV.1.1 The same group also d
Page 185 and 186: IV.1.3: Present work Although sever
Page 187 and 188: O O C 6 H 13 i O C 6 H 13 ii OH C 6
Page 189 and 190: Fig. IV.1.4. 1 H NMR spectrum of 10
Page 191 and 192: the unit-C contribute positively to
Page 193 and 194: tartrate, Ti(O-i-Pr) 4 , CH 2 Cl 2
Page 195 and 196: Based on this hypothesis, the alcoh
Page 197 and 198: OR 3 O R 1 R 2 NaBH 4 H H R 1 R 1 +
Page 199 and 200: (OH). Oxidative cleavage of its α-
Page 205 and 206: IIV. .33: : SSYNTHESSIISS OFF 33' '
Page 207 and 208: For the actual synthesis, (Scheme I
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Fig. IV.3.1. 1 H NMR spectrum of 14
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IV.4: SSYNTHESSIISS OFF 22( (SS) )-
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(i) PhCHO, triethyl orthoformate, M
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O N 3 II Ph HO OH b1 N 3 Ph O O Ben
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Thus, easily accessible 1 has been
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167 and subsequent reduction gave 1
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from the appearance of 13 C NMR pea
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IV.6 EXPERIMENTAL SECTION (2R,3S,4R
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As described earlier, compound 108
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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
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(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
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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
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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
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119. Wender, P. A.; Holt, D. A.; Si
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140. (a) Chemler, S. R.; Roush, W.
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Lett. 1996, 107, 53. (c) Smith, C.
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158. Mitsuya, H.; Weinhold, K. J.;
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L.; Zugay, J. A. J. Med. Chem. 1993
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1. Goswami, D.; Chattopadhyay, A.;
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