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2005
Benzopyran derivatives
R 0350
Synthesis of Chiral Chromans by the Pd-Catalyzed Asymmetric Allylic Alkylation
Scope, Mechanism, and Applications. — Under optimized conditions, phe05- 120 (AAA):
nol allyl carbonates undergo enantioselective cyclization under catalysis of chiral palladium catalyst derived from known Trost ligand (I). Interestingly, both (E) and (Z)-isomers of tri- and disubstituted carbonates are converted into (R)-chromans by use of
ligands of opposite chirality. In the series of trisubstituted carbonates, the (Z)-isomers
(IV) afford the chromans in significantly higher e.e. values than the (E)-counterparts,
whereas reversed selectivities are observed for disubstituted carbonates (V) and (VII).
The effect of pH, the influence of the olefin geometry, and the substitution pattern on
the e.e. and the absolute configuration of the resulting chromans is studied in detail.
The method enables the enantioselective synthesis of the vitamin E core, the first enantioselective total synthesis of (+)-clusifoliol and (-)-siccanin, and the synthesis of an
advanced intermediate toward (+)-rhododaurichromanic acid A. — (TROST*, B. M.;
SHEN, H. C.; DONG, L.; SURIVET, J.-P.; SYLVAIN, C.; J. Am. Chem. Soc. 126
(2004) 38, 11966-11983; Dep. Chem., Stanford Univ., Stanford, CA 94305, USA;
Eng.) — Klein
2005
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