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Synthesis of alkenes by isomerizations
Recent Literature
O3ReOSiPh3 promotes the 1,3-isomerization of various
allylic alcohols. Two different strategies allow the selective formation of
a single isomer. The first strategy utilizes the formation of a conjugated
alkene to ensure a high selectivity. The second strategy employs N,O-bis(trimethylsilyl)acetamide
(BSA) as an additive to remove the product from the reaction equilibrium and
works well for the isomerization of tertiary allylic alcohols.
C. Morrill, R. H. Grubbs, J. Am. Chem. Soc.,
2005, 127, 2842-2843.
C. Morrill, R. H. Grubbs, J. Am. Chem. Soc.,
2005, 127, 2842-2843.
Lithium diisopropylamide (LDA) promotes virtually quantitative conversion of
allylic ethers to (Z)-propenyl ethers with very high stereoselectivity in
THF at room temperature. The reaction time for the conversion increases with
more sterically hindered allylic ethers.
C. Su, P. G. Williard, Org. Lett., 2010,
12, 5378-5381.
Substituted benzofurans were synthesized from their corresponding substituted
1-allyl-2-allyloxybenzenes using ruthenium-catalyzed C- and O-allyl
isomerization followed by ring-closing metathesis.
W. A. L. van Otterlo, G. L. Morgans, L. G. Madeley, S. Kuzvidza, S. S. Moleele,
N. Thornton, C. B. de Koning, Tetrahedron, 2005,
61, 7746-7755.
A hydroxyl group-directed, highly regio- and stereoselective transposition of
allylic alcohols based on rhenium catalysis is suitable for a direct
isomerization of acetals into the thermodynamically preferred isomer as long as
one of the hydroxyl groups is allylic. This method will expand the scope of
rhenium-catalyzed alcohol transpositions for complex molecule synthesis.
A. T. Herrmann, T. Saito, C. E. Stivala, J. Tom, A. Zakarian, J. Am. Chem. Soc., 2010,
132, 5962-5963.
Pd(PPh3)4-catalyzed isomerization of
methylenecyclopropanes (MCPs) proceeds smoothly
at 80°C in acetic acid and toluene to give 1-substituted or 1,1-disubstituted
dienes in good to excellent yields. The mechanism is discussed.
M. Shi, B.-Y. Wang, J.-W. Huang, J. Org. Chem., 2005, 70, 5606-5610.
Aryl-substituted cyclopropyl carbinol derivatives undergo a facile
stereoselective rearrangement catalyzed by In(OTf)3 in
dichloromethane under sonication to produce the substituted conjugated all-trans-butadienes.
B. C. Ranu, S. Banerjee, Eur. J. Org. Chem., 2006, 3012-3015.
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