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2001
diastereoselective syntheses, enantioselective syntheses
diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism)
O 0031
The Magnesium–Ene Cyclization Stereochemically Directed by an
16 - 041 Allylic Oxyanionic Group and Its Application to a Highly Stereoselective Synthesis of (±)-Matatabiether. Allylmagnesium Compounds by
Reductive Magnesiation of Allyl Phenyl Sulfides. — A method for the
generation of allylmagnesium intermediates is developed avoiding the presence
of lithium ions. Thus, treatment of allyl or benzyl phenyl sulfide precursors such
as (I), (V), and (VIII) with activated magnesium (sonication of a mixture of
Mg, anthracene and dibromoethane in THF) affords these intermediates which
can undergo cyclization or can be trapped with electrophiles. The usefulness
of this reductive magnesiation method is demonstrated with the synthesis of
terpene (IV) via selenide (III), which is obtained with higher diastereoselectivity
from the conjugate base derived from alcohol (I) [by deprotonation of (I) with
MeMgBr], than by a method employing lithium ions. — (CHENG, DAI; ZHU,
SHIRONG; YU, ZHIFANG; COHEN, THEODORE; J. Am. Chem. Soc. 123
(2001) 1, 30-34; Dep. Chem., Univ. Pittsburgh, Pittsburgh, PA 15260, USA;
EN)
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