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2005
Terpenes
U 0200
33- 220
Stereoselective Synthesis of 19-Hydroxytaxoid by Utilizing Samarium(II) Iodide-Mediated Double Aldol Cyclization. — The synthesis of taxane's basic skeleton
starts with the construction of the B-ring (III) by intramolecular samarium iodide-mediated double aldol cyclization of the optically active polyoxy unit (II). Bicyclic compound (V), corresponding to the BC-ring system of 19-hydroxytaxol, is prepared from
the key intermediate (III) by successive trimethylaluminum-assisted stereoselective
conjugated addition and intramolecular samarium iodide-mediated double aldol cyclization, cf. (IV)→(V). BC-ring unit (VIII), precursor of the ABC ring system, is constructed via stereoselective homoallylation. Intramolecular pinacol coupling of (VIII)
using low-valent titanium reagent affords ABC-ring (IX) as main product. Finally, the
synthesis of the new 19-hydrotaxoid (XI) is accomplished from system (IX) by olefination of the vicinal diol unit in (X). — (OGAWA, Y.; KURODA, K.; MATSUO, J.-I.;
MUKAIYAMA*, T.; Bull. Chem. Soc. Jpn. 78 (2005) 4, 677-697; Kitasato Inst.,
Cent. Basic Res., Kita, Tokyo 114, Japan; Eng.) — H. Hoennerscheid
2005
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