Synthesis of cyclopropanes via iodine–magnesium exchange between 3-iodomethyl-1-oxacyclopentanes and organomagnesium reagents
摘要:
Iodine-magnesium exchange occurs upon treatment of 3-iodomethyl-1-oxacyclopentanes with alkyl Grignard reagents or trialkylmagnesate. The resulting organomagnesium compounds undergo intramolecular nucleophilic substitution in ether to afford cyclopropane skeletons in a stereoselective manner. (C) 2003 Elsevier Ltd. All rights reserved.
作者:Andrew L. Kocen、Maurice Brookhart、Olafs Daugulis
DOI:10.1039/c7cc04953f
日期:——
We report a method for palladium-catalysed chain-running isomerization of terminal and internal alkenes. Using an air-stable 2,9-dimethylphenanthroline-palladium catalyst in combination with NaBAr4 promoter, olefins are converted to the most stable double bond isomer at −30 to 20 °C. Silyl enol ethers are readily formed from silylated allylic alcohols. Fluorinated substituents are compatible with the
disubstituted γ-lactol 1e were converted into tetrahydrofuran derivatives by reaction with typical silylenolethers in the presence of Lewis acids. Although the most suitable Lewis acid appears to be zinc chloride, BF3·Et2O or diethylaluminium chloride are also suitable under appropriate conditions. The stereoselectivities of these substitution reactions are similar to those observed with other silylated nucleophiles;
Radical addition of triphenylgermane to vinyloxiranes proceeded in the presence of triethylborane to yield 4-triphenylgermyl-2-buten-1-ol derivatives in good yields. Iodo acetals, prepared by iodoetherification of vinyl ethers with the obtained allylic alcohol, underwent radical cyclization to give 2-alkoxy-4-vinyltetrahydrofurans, which were converted into 4-vinyltetrahydro-2-furanones by Jones oxidation. The cyclization involved fragmentation of β-triphenylgermyl radical.
Isomerization of Allyl Ethers Initiated by Lithium Diisopropylamide
作者:Chicheung Su、Paul G. Williard
DOI:10.1021/ol102029u
日期:2010.12.3
Lithium diisopropylamide (LDA) promotes virtually quantitative conversion of allylic ethers to (Z)-propenyl ethers. It was discovered that allylic ethers can be isomerized efficiently with very high stereoselectivity to (Z)-propenyl ethers by LDA in THF at room temperature. The reaction time for the conversion increases with more sterically hindered allylic ethers. Different amides were also compared with LDA for their ability to effect this isomerization.
Hippeli, Claudia; Reissig, Hans-Ulrich, Liebigs Annalen der Chemie, 1990, p. 217 - 226