Synthesis of 1,4-dienes
In situ generated palladium(0) nanoparticles catalyze an efficient cross-coupling of allyl acetates with aryl and vinyl siloxanes. The reactions are stereoselective, and linear (E)-coupling products are obtained both from cis and trans allyl acetates. The coupling with vinyl siloxanes provides a novel protocol for the synthesis of 1,4-pentadienes.
R. Dey, K. Chattopadhyay, B. C. Ranu, J. Org. Chem., 2008, 73, 9461-9464.
Alkenyltrifluoroborates can be cross-coupled with allyl and benzyl chlorides using KOH as base in acetone-water (3:2) at 50 °C and low catalyst loadings of a 4-hydroxyacetophenone oxime derived palladacycle giving the corresponding 1,4-dienes and allylarenes, respectively. The use of overheated water as solvent and K2CO3 as base allows a coupling of alkenyltrifluoroborates with aryl and heteroaryl bromides.
E. Alacid, C. Nájera, J. Org. Chem., 2009, 74, 2321-2327.
A microwave synthesis of 1,4-pentadienes has been developed involving the palladium-catalyzed cross-coupling of potassium vinyltrifluoroborates with allyl acetates.
G. W. Kabalka, M. Al-Masum, Org. Lett., 2006, 8, 11-13.
An enhanced Lewis acid system of InCl3 and Me3SiBr can be used to promote a wide range of direct coupling reactions between alcohols and silyl nucleophiles in non-halogenated solvents. Highly chemoselective allylations toward a hydroxyl moiety over ketone and acetoxy ones have been demonstrated.
T. Saito, Y. Nishimoto, M. Yasuda, A. Baba, J. Org. Chem., 2006, 71, 8516-8522.
The Pd(0)-catalyzed allylic cross-coupling of homoallylic tosylate substrates using boronic acids and pinacol esters uses 2-(4,5-dihydro-2-oxazolyl)quinoline (quinox) as a ligand and is performed at ambient temperature. The scope of the reaction is broad in terms of both the boronate and the tosylate, that includes secondary tosylates.
B. J. Stokes, S. M. Opra, M. S. Sigman, J. Am. Chem. Soc., 2012, 134, 11408-11411.
A mild, cobalt-catalyzed 1,4-hydrovinylation of acyclic 1,3-dienes with various functionalized terminal alkenes is described. Unsymmetrical 1,3-dienes yield products, where the new carbon-carbon bond is formed at the less substituted end of the 1,3-diene.
G. Hilt, S. Lüers, Synthesis, 2002, 609-618.
In cobalt-catalyzed 1,4-hydrovinylation, dppe/dppp ligands led to the formation of the branched product, whereas the SchmalzPhos ligand generates the corresponding linear product in both excellent yields and regioselectivities. The catalyst exhibits a high tolerance toward functional groups, and the very mild reaction conditions allow the synthesis of 1,4-dienes without isomerization into conjugated systems.
M. Arndt, M. Dindaroğlu, H.-G. Schmalz, G. Hilt, Org. Lett., 2011, 13, 6184-6187.
Monosubstituted acyclic (E)-1,3-dienes undergo efficient hydrovinylation giving (Z)-3-alkylhexa-1,4-dienes upon treatment with catalytic amounts of bidentate phosphine-CoCl2 complexes and Me3Al in an atmosphere of ethylene. Complexes derived from (RR)-DIOP and (SS)-BDDP at -45°C give very high enantioselectivities for several prototypical 1,3-dienes.
R. K. Sharma, T. V. RajanBabu, J. Am. Chem. Soc., 2010, 132, 3295-3297.
A nickel-catalyzed intermolecular process for direct allylation of nonconjugated, nonstrained simple alkenes affords the desired linear 1,4-dienes in high yield in both gram-scale and smaller scale coupling reactions.
R. Matsubara, T. F. Jamison, J. Am. Chem. Soc., 2010, 132, 6880-6881.
Sulfonate bearing chiral bidentate N-heterocyclic carbene (NHC) complexes promote catalytic enantioselective allylic substitution reactions, which involve the use of alkyl- or aryl-substituted vinylaluminum reagents and afford 1,4-dienes containing a quaternary carbon stereogenic center at their C-3 site.
F. Gao. K. P. McGrath, Y. Lee, A. H. Hoveyda, J. Am. Chem. Soc., 2010, 132, 14315-14320.
Vinylaluminum reagents prepared from the reaction of commercially available DIBAL-H and a terminal alkyne can be used directly without purification in catalytic asymmetric allylic alkylation reactions with allylic phosphates in the presence of a readily available chiral N-heterocyclic carbene (NHC) complex and a commercially available and air stable Cu salt.
Y. Lee, K. Akiyama, D. G. Gillingham, M. Kevin Brown, A. H. Hoveyda, J. Am. Chem. Soc., 2008, 130, 446-447.
Use of copper(I) tert-butoxide and allylic halides enables the substitution of the silyl group in vinylsilanes by an allylic group. This synthetic application of a 1,3 Csp2-to-O silyl migration provides a useful method for the generation of vinyl anion equivalents.
A. Tsubouchi, M. Itoh, K. Onishi, T. Takeda, Synthesis, 2004, 1504-1508.
An efficient synthetic method provides tri- and tetra-substituted allenes by the reaction of allylindium reagents with 3°-propargyl alcohols. Allylindium reagents are generated in situ from indium and allyl bromides.
K. Lee, P. H. Lee, Org. Lett., 2008, 10, 2441-2444.
Sulfonate-bearing chiral bidentate N-heterocyclic carbene (NHC) complexes of copper enable catalytic enantioselective allylic substitutions of allylic phosphonates with commercially available allenylboronic acid that result in addition of an allenyl group and formation of tertiary or quaternary C-C bonds in up to 95% yield, >98% SN2′ selectivity, and 98% ee.
B. Jung, A. H. Hoveyda, J. Am. Chem. Soc., 2012, 134, 1490-1493.
On exposure to BuLi, 3-bromo-2-iodocyclopent-2-enol O-TBS ether undergoes iodine-lithium permutation with complete regioselectivity. Reaction with different electrophiles affords the corresponding 2-substituted-3-bromocyclopentenol derivatives. Subsequent bromo-lithium exchange with t-BuLi, followed by reaction with an equal or different electrophile, affords 2,3-disubstituted cyclopentenols.
M. Luparia, A. Vadalŕ, G. Zanoni, G. Vidari, Org. Lett., 2006, 8, 2147-2150.