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2001
addition reactions
addition reactions
O 0060
Reaction of Alkyl and Aryl Grignard Reagents with Trifluo16 - 048 roacetyldihydropyrans and Other Cyclic β-Alkoxy-α,β-unsaturated
Trifluoromethylketones.
— Reaction of aryl and alkyl Grignard reagents
with title ketones (II) proceeds by 1,4-addition to give cis-2,3-disubstituted
tetrahydropyrans (III) in a stereoselective manner. Side products (IV) arise
from ring opening of the initial 1,4-adducts and recyclization. In comparison, in
the reaction of ketone (IIa) with BuLi (Vb) the selectivity of 1,4- to 1,2-addition
is decreased in comparison to BuMgBr (Va). Addition of aryl Grignard reagents
to the alkoxy-substituted analogue (X) proceeds predominantly by ring opening
and addition of further equivalents of aryl Grignard reagent. 1,4-Adducts
analogous to compounds (III), namely (XV), are obtained at low temperatures
only.
— (MELLOR, JOHN M.; REID, GILL; EL-SAGHEER, AFAF H.;
EL-TAMANY, EL-SAYED H.; Tetrahedron 56 (2000) 51, 10039-10055; Dep.
Chem., Univ. Southampton, Southampton SO17 1BJ, UK; EN)
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