151671-04-4Relevant articles and documents
Dynamic ligand exchange of the lanthanide complex leading to structural and functional transformation: One-pot sequential catalytic asymmetric epoxidation-regioselective epoxide-opening process
Tosaki, Shin-Ya,Tsuji, Riichiro,Ohshima, Takashi,Shibasaki, Masakatsu
, p. 2147 - 2155 (2007/10/03)
The characteristic property of the lanthanide complex, which easily undergoes a dynamic ligand exchange and alters its structure and function in situ, is described. After the completion of the catalytic asymmetric epoxidation of various α,β-unsaturated amides 2 in the presence of the Sm-(S)-BINOL-Ph3-As=O (1:1:1) complex 1 (2-10 mol %), the addition of Me3SiN3 directly to the reaction mixture led to smooth epoxide-opening at room temperature, affording the corresponding anti-β-azido-α-hydroxyamide 4 in excellent overall yield (up to 99%) with complete regioselectivity and excellent enantiomeric excess (up to >99%). The key to the success of the sequential process was the in situ generation of the highly reactive samarium azide complex through dynamic ligand exchange. In situ IR spectroscopy and other experiments provided strong evidence that the samarium azide complex was generated. In addition, the relatively high Lewis basicity of the amide moiety had a key role in the high reactivity of both the epoxidation and the epoxide-opening reactions. Examinations of other nucleophiles such as sulfur or carbon nucleophiles as well as transformations of epoxide-opened products are also described.
Asymmetric Synthesis of the Taxol and Taxotere C-13 Side Chains
Bunnage, Mark E.,Davies, Stephen G.,Goodwin, Christopher J.
, p. 2385 - 2392 (2007/10/02)
A practical and efficient asymmetric synthesis of the 3-benzoylamino-2-hydroxy-3-phenylpropionic acid derived side chain of the important anticancer agent taxol is described.The pivotal synthetic transformation relies upon the highly diastereoselective tandem lithium amide conjugate addition-electrophilic hydroxylation of tert-butyl cinnamate 4.The resultant anti β-amino-α-hydroxy acid derivative is readily converted to the anti diastereomer of the taxol side chain methyl ester, from which the naturally occuring syn configuration is secured by a simple Mitsunobu inversion sequence via a dihydrooxazole intermediate.Under optimal conditions, this straightforward approach provides the taxol side chain methyl ester (-)-15 (natural enantiomer) in four steps and 60percent yield from tert-butyl cinnamate 4.The protocol is applied to the preparation of all four taxol side chain stereoisomers and is extended to allow for the synthesis of the side chain of taxotere, a potent taxol analogue.
