Low-Valent Titanium Induced Carbonyl Coupling Reactions

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3.1.2 Mixed Carbonyl Coupling Reactions Intermolecular carbonyl coupling reactions are usually limited to the preparation of symmetrical olefins by the reductive dimerization of a ketone or an aldehyde. A mixture of two different carbonyl compounds will react generally to a nearly statistical mixture of olefins when subjected to low-valent titanium[33,34]. For the purposes of synthesis, such mixed couplings are only useful only if one component is used in excess and if the products are easily separable[24]. For example, mixed coupling of acetone with a chiral α,β-unsaturated ketones like (R)-(-)- (4-methylcyclohexylidene)acetone affords a diene (9)initially prepared by Walborsky for chiroptical study[35]. C H 3 14 8 C H 3 H O + C H 3 O TiCl 4/LiAlH 4 CH 3 C H 3 C H 3 Another example of a mixed coupling reaction is the reaction of an equimolar amount of 2,6dimethyl-2-cyclohexenone (10) and formyl(trimethylsilyl)cyclopropane (11) with low-valent titanium. Paquette[36] prepared sesquiterpene vetispirene (12) by this method with a yield of 60%. There is however, no apparent justification why the mixed product should be so strongly favoured over the symmetrical products in this case. C H 3 10 O CH 3 + 11 SiMe 3 CHO TiCl 3/Zn-Cu 60 % 9 CH 3 CH 3 C H 3 H SiMe 3 Mixed carbonyl coupling reaction has paved the way for the synthesis of the antitumor agent tamoxifen (15) and several of its analogs[37,38]. 12 CH 3
CH 3 13 O + O X R 14 3.1.3 Functional Group Compatibility R = OCH 2CH 2NMe 2 C H 3 X R 15 X = H, Tamoxifen Several easily reducible functional groups do not survive in the presence of low-valent titanium due to the strong reducing potential of this reagent. Acetal. Not many carbony coupling reactions are known to take place in the presence of acetal groups[]. Clive reported[39] the coupling of acetal (16) in the course of compactin (17) synthesis. OHC OSMDBT 16 OSiEt 3 O O O CH 3 CH 3 CH 3 TiCl 3/C 8K 85 % OSMDBT OSiEt 3 17 O O CH 3 8 % CH 3 CH 3 15
Page 1: Walter Sisulu University PROFESSORI
Page 5 and 6: LOW-VALENT TITANIUM-INdUCEd CARbONy
Page 7 and 8: problems, thus opens up the way for
Page 9 and 10: 2 O R R' 2 x e- 2 O- R R' . Deoxyge
Page 11 and 12: OH CH3 OH CH3 1 OH OH 2 = = HO OH O
Page 13: Table 2. Synthesis of Strained Olef
Page 17 and 18: Amines. Amines are inert towards lo
Page 19 and 20: Ketone. Ketones do in fact survive
Page 21 and 22: Table 3. Intramolecular Dicarbinyl
Page 23 and 24: Scheme 7 Keto-enol tautomerism[63]
Page 25 and 26: R 1 47 O O O R 2 Ti/Graphite THF, r
Page 27 and 28: the synthesis of indoles from acyla
Page 29 and 30: 60 C H 3 NH O O O Ti/Graphite in DM
Page 31 and 32: R 1 R 2 N CH 3 Table 9. Titanium in
Page 33 and 34: 7. CONCLUSION Almost any of the org
Page 35 and 36: 20. B. P. Mundy, R. Srinivasa, Y. K
Page 37 and 38: 58. 59. 60. J. E. McMurry, G. J. Ha
Page 39 and 40: ACKNOWLEdGEMENT I would like to tha
Page 44: 44 Design: Mthatha Health Resource

Low-Valent Titanium Induced Carbonyl Coupling Reactions

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