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3-alkoxy-2-en-1-ones has been reported. 25 I have also recently studied the synthesis of 5-chloroethyl-2-(arylthio)benzoates by TiCl4-mediated domino ′[3+3] cyclization / homo-Michael′ reaction of 3-arylthio-1-trimethylsilyloxy-1,3-butadienes with 1,1diacylcyclopropanes. 26 Herein, I provide a full account of this work. In addition, I report a comprehensive study related to the formal [3+3] cyclization of 3-arylthio-1trimethylsilyloxy-1,3-butadienes with 3-silyloxy-2-en-1-ones. The reactions reported provide a convenient approach to substituted 2-(arylthio)benzoates and thioxanthones which are not readily available by other methods. 1.2 Result and Discussions. The reaction of β-ketoesters 1a-c with various thiophenols gave, following the procedure reported by Chan et al., 22,23 the 3-(arylthio)alkanoates 2a-k (Scheme 1). Deprotonation of 2a-k (LDA) and subsequent addition of Me3SiCl afforded, again following the procedure reported by Chan et al., 22,23 the 3-arylthio-1-silyloxy-1,3butadienes 3a-m. The synthesis of 2a and 3a has been previously reported. Dienes 3a-m proved to be unstable and had to be used directly after their preparation. R 1 O 1a-c R 1 O OMe SAr ArSH 3a-m (78-96%) i OSiMe 3 OMe 14 R 1 SAr O 2a-k (76-94%) ii OMe Scheme 1. Synthesis of 3a-m (for R 1 and Ar, see Table 1); conditions: i, P4O10, CH2Cl2, 20 °C, 18 h; ii, 1) LDA, THF, −78 °C, 1 h; 2) Me3SiCl, −78 → 20 °C, 14 h
3-Arylthio-1-trimethylsilyloxy-1,3-butadienes 3a-m were prepared, as previously reported, by reaction of methyl acetoacetate (1a), methyl 3-oxopentanoate (1b), and methyl 3-oxohexanoate (1c) with various thiophenols to give methyl 3- (arylthio)crotonates 2a-m. The latter were subsequently transformed into 3a-m by deprotonation (LDA) and subsequent silylation. The TiCl4-mediated cyclization of 3a with 3-silyloxy-2-en-1-one 4a, prepared from acetylacetone, afforded the 2- (phenylthio)benzoate 5a (Scheme 1). The best yields were obtained when the reaction was carried out in a highly concentrated solution (stoichiometric ratio: 3a/4a/ TiCl4 = 1.0/1.5/1.5). The solution was slowly warmed from −78 to 20 °C (20 h). The formation of 5a can be explained by reaction of 4a with TiCl4 to give intermediate A. The attack of the terminal carbon atom of 3a onto A afforded intermediate B. The elimination of TMS-siloxane (intermediate C) and subsequent cyclization gave intermediate D. The elimination of titanium hydroxide (before or during the aqueous work-up) and aromatization resulted in the formation of product 5a. Due to the symmetrical structure of A, the attack of 1a on either terminal allylic carbon atom would result in the formation of the same product (5a). The cyclization of dienes 3a-m with 3-silyloxy-2-en-1-ones 4a-f afforded the 2- (thioaryloxy)benzoates 5a-v (Scheme 3, Table 1). Noteworthy, products 5e, 5h and 5k were formed with very good regioselectivity (vide infra). For 5h and 5k, this result is in agreement with the regiochemical result of the reaction of 4f with 1,3bis(silyloxy)-1,3-butadienes. 12,15 The reaction of 1,3-bis(silyloxy)-1,3-butadienes with 4e has not been previously studied. The yields of products 5 depend on the substituents of dienes 3. This can be seen by comparison of the yields of products derived from the same electrophile and different dienes (or vice versa). The comparison of the yields of 5b, 5f, and 5i (or of 5c, 5g, and 5j) show that higher yields are often obtained for products derived from dienes containing an alkyl group attached to carbon C-4 of the diene. However, this effect is not general. The aryl group of the diene also has some influence. The yields of the products derived from dienes containing an electron-rich aryl group (5a,l,o) are higher than the products derived from dienes containing electron-poor aryl groups (5q,t,u). No clear trend is observed for the influence of the 3-silyloxy-2-en-1-one 4. 15
Page 1 and 2: Synthesis of functionalized 2-(aryl
Page 3 and 4: The ink of the scholar is more holy
Page 5 and 6: Affectionately Dedicated to “All
Page 7 and 8: Table of Contents 03 List of used a
Page 9 and 10: RCM Ring Closing Metathesis TBAI Te
Page 11 and 12: humans: 1) the thiomethyl of methio
Page 13 and 14: Chart 3. Structure of sumatriptan S
Page 15 and 16: disulfide (DADS) and diallyl sulfid
Page 17: 1. Synthesis of functionalized 2-(a
Page 21 and 22: under kinetic reaction control, by
Page 23 and 24: l a u 4-FC6H4 H Me H 40 m a v 4-FC6
Page 25 and 26: Table 2. Synthesis of thioxanthones
Page 27 and 28: 3a O OSiMe 3 O OMe + Me Me Cl 3TiO
Page 29 and 30: Table 3. Synthesis of 8a-x 3 7 8 Ar
Page 31 and 32: Cl + SPh OSiMe 3 3a 9 O OMe O O H i
Page 33 and 34: solution. The use of an excess (1.5
Page 35 and 36: Table 4. Synthesis of 12a-r 3 11 12
Page 37 and 38: 2.3 Conclusion In conclusion, I hav
Page 39 and 40: aromatization). An unseparable 1:2
Page 41 and 42: Table 5. Synthesis of arenes 14a-l
Page 43 and 44: 3.3 Conclusion In conclusion, I hav
Page 45 and 46: Mass Spectroscopy: AMD MS40, AMD 40
Page 47 and 48: 131.0 (ArCH), 132.7, 134.0, 135.9,
Page 49 and 50: (EI, 70 eV): m/z (%): 380 (100), 21
Page 51 and 52: (m), 1490 (m), 1434 (m), 1383 (w),
Page 53 and 54: 15.4, 16.9, 18.9 (CH3), 28.3 (CH2),
Page 55 and 56: (C). IR (neat): ν̃ = 2945 (w), 29
Page 57 and 58: 948 (w) 853 (m), 803 (m), 751 (m),
Page 59 and 60: 135.4, 139.2, 143.8, 146.5, 182.2 (
Page 61 and 62: Me S O Me Ph Br Methyl 4-methyl-5-(
Page 63 and 64: 35 Cl, 37 Cl, 61), 430 (M + , 35 Cl
Page 65 and 66: ArH). 13 C NMR (62 MHz, CDCl3): δ
Page 67 and 68: Me S O Me Me Methyl 4,6-dimethyl-5-
Page 69 and 70:
S Methyl 4-methyl-5-(2-bromoethyl)-
Page 71 and 72:
(CH2CH3), 33.3 (CH2), 40.1 (CH2), 5
Page 73 and 74:
Me 3,4-Dimethyl-2-phenylsulfanyl-be
Page 75 and 76:
Me 3,4-Dimethyl-2-(p-tolylsulfanyl)
Page 77 and 78:
OCH3), 7.08-7.17 (m, 7H, Ar); 13 C
Page 79 and 80:
(w), 750 (s), 732 (s), 688 (s), 650
Page 81 and 82:
35 Cl 35 Cl, 100), 359 (26), 357 (3
Page 83 and 84:
2924 (w), 2853 (w), 1728 (s), 1712
Page 85 and 86:
Me 3-Hydroxy-5-(4-methylphenylsulfa
Page 87 and 88:
Et 3-Hydroxy-5-(4-ethylphenylsulfan
Page 89 and 90:
(13), 264 (13), 262 (36) ,260 (12),
Page 91 and 92:
MS (EI, 70 eV): m/z (%) = 337 (16),
Page 93 and 94:
OH O 5'-Hydroxy-[1,1';3',1'']terphe
Page 95 and 96:
Refrences 1. Handbook of Chemistry
Page 97 and 98:
20. For a review of [3+3] cyclizati
Page 99 and 100:
Nationality Pakistan Place of Birth
Page 101 and 102:
Publications 1. Inam Iqbal, Muhamma
Page 103 and 104:
Tetrahedron 2007, 63, 12562-12575.
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List of used abbreviations - RosDok - Universität Rostock

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