Allylic Substitutions, Allylation
The reaction of secondary and tertiary alkyl halides with benzylic or allylic Grignard reagents in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reaction provides efficient access to quaternary carbon centers.
H. Someya, H. Ohmiya, H. Yorimitsu, K. Oshima, Org. Lett., 2008, 10, 969-971.
Efficient enantioselective Cu-catalyzed alkylations of aromatic and aliphatic allylic phosphates bearing di- and trisubstituted olefins are promoted in the presence of a readily available chiral amino acid-based ligand. Tertiary and quaternary stereogenic carbon centers are delivered regioselectively in high ee.
M. A. Kacprzynski, A. H. Hoveyda, J. Am. Chem. Soc., 2004, 126, 10676-10681.
Direct Csp3−Csp3 coupling of various aliphatic trimethylsilyl ethers and allylsilanes is effectively catalyzed by InCl3 and I2. The transformation probably involves an in situ-derived combined Lewis acid of InCl3 and Me3SiI. The reaction allows the construction of quaternary-quaternary and quaternary-tertiary carbon-carbon bonds and tolerates aryl halide moieties.
T. Saito, Y. Nishimoto, M. Yasuda, A. Baba, J. Org. Chem., 2007, 72, 8588-8590.
A promising new approach to a generalized allylation process uses various easily accessible allyl diphenylphosphine oxides as radical trapping agents for the allylation of ditihocarbonates.
G. Ouvry, B. Quiclet-Sire, S. Z. Zard, Angew. Chem. Int. Ed., 2006, 45, 5002-5006.
The palladium-catalyzed reaction of allyl acetates with aryl- and vinyltin reagents gave good yields of cross-coupled products. The reaction was mild and tolerant of functionality (-CO2R, -OH, -OSiR3, -OMe) in the tin reagent. Inversion of stereochemistry at the acetate center was observed, with retention of the geometry of the olefin of the allyl group and with exclusive coupling at the primary position. Retention of geometry of the olefin in the vinyltin reagents was also observed.
L. Del Valle, J. K. Stille, L. S. Hegedus, J. Org. Chem, 1990, 55, 3019-3023.
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.
In a Pd-catalyzed cross-coupling of aromatic and aliphatic allylic carbonates and allylB(pin), small-bite-angle ligands favor the branched substitution product. This mode of regioselection is consistent with a reaction that operates by a 3,3′ reductive elimination reaction. In the presence of appropriate chiral ligands, this reaction is rendered enantioselective.
P. Zhang, L. A. Brozek, J. P. Morken, J. Am. Chem. Soc., 2010, 132, 10686-10688.
A palladium-catalyzed cross-coupling of allyl boronates and chiral propargyl delivers chiral 1,5-enynes with excellent levels of chirality transfer. The reaction can be applied across a broad range of substrates.
M. J. Ardolino, J. P. Morken, J. Am. Chem. Soc., 2012, 134, 8770-8773.
The Suzuki-Miyaura cross-coupling reaction between a diborylmethane derivative and allyl halides or benzyl halides proceeded efficiently in the presence of an appropriate Pd-catalyst at room temperature. The present approach provides functionalized homoallylboronates and alkylboronates with excellent regio- and chemoselectivities.
K. Endo, T. Ohkubo, T. Ishioka, T. Shibata, J. Org. Chem., 2012, 77, 4826-4831.
Allylsilylation allows to install both silyl and allyl groups onto a carbon-carbon double bond directly. Proton-exchanged montmorillonite showed excellent catalytic performances for the allylsilylation of alkenes. Isolation of the reaction intermediate on the montmorillonite surface helped to investigate the reaction mechanism.
K. Motokura, S. Matsunaga, A. Miyaji, Y. Sakamoto, T. Baba, Org. Lett., 2010, 12, 1508-1511.
Enantioselective copper-catalyzed allylic alkylations of Grignard reagents were performed on allylic bromides with a protected hydroxyl or amine functional group using Taniaphos as a ligand. The terminal olefin moiety in the products can be transformed into various functional groups without racemization.
A. W. van Zijl, F. López, A. J. Minnaard, B. L. Feringa, J. Org. Chem., 2007, 72, 2558-2563.
A chemo- and regioselective, Cu-catalyzed asymmetric addition of Grignard reagents to 3-bromopropenyl esters provides allylic esters in high yields and enantioselectivities using Taniaphos as ligand. The method is a practical route to chiral, nonracemic allylic alcohols.
K. Geurts, S. P. Fletcher, B. L. Feringa, J. Am. Chem. Soc., 2006, 128, 15572-15573.
The use of catalytic loadings of picolinaldehyde and Ni(II) salts in catalytic α-allylation of unprotected amino acid esters induces preferential reactivity at the enolizable α-carbon over the free nitrogen with electrophilic palladium π-allyl complexes to produce α-quaternary α-allyl amino acid esters. Additionally, the use of chiral ligands to access enantioenriched α-quaternary amino acid esters from racemic precursors is demonstrated.
P. Fang, M. R. Chaulagian, Z. D. Aron, Org. Lett., 2012, 14, 2130-2133.
Chelated amino acid ester enolates are excellent nucleophiles for allylic alkylations. With these enolates, even terminal π-allyl palladium complexes react without significant isomerization.
K. Krämer, U. Kazmaier, J. Org. Chem., 2006, 71, 8950-8953.
The use of unsaturated methylidene ketones in catalytic conjugate allylations allows a significant expansion in substrate scope and occurs in a highly enantioselective fashion in the presence of a Taddol-derived phosphinite ligand.
L. A. Brozek, J. D. Sieber, J. P. Morken, Org. Lett., 2011, 13, 995-997.
The reaction of alkoxides with boron trichloride results in the generation of cations that can be allylated in subsequent transformations. The absence of Brønsted acids can make a significant difference in such syntheses.
G. W. Kabalka, M.-L. Yao, S. Borella, J. Am. Chem. Soc., 2006, 128, 11320-11321.
Aryl aldehydes couple readily with allylmetals to afford haloallylated products in the presence of boron trihalides. The reactions tolerate a variety of functional groups. Simple aqueous workup of haloallylation reactions, followed by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene, provides a straightforward route to synthetically useful (E)-1,3-dienes.
M. P. Quinn, M.-L. Yao, G. W. Kabalka, Synthesis, 2011, 3815-3820.
Various acetals or alcohols react with allyl(trimethyl)silane or 1-phenyl-2-(trimethylsilyl)acetylene in the presence of a catalytic amount of the Brønsted acid o-benzenedisulfonimide under mild conditions to give good yields of the allylated products. The catalyst can be easily recovered and purified for use in further reactions.
M. Barbero, S. Bazzi, S. Cadamuro, S. Dughera, C. Piccinini, Synthesis, 2010, 315-319.
Allylic gem-dichlorides undergo regio- and enanantioselective copper-catalyzed allylic alkylation with Grignard reagents to afford chiral Z-vinyl chlorides. Subsequent Suzuki cross coupling reactions afford optically active Z-alkenes and 1,3-cis,trans dienes.
M. Giannerini, M. Fañanás-Mastral, B. L. Feringa, J. Am. Chem. Soc., 2012, 134, 4108-4111.
In the “deacylative allylation”, the coupling partners, ketone pronucleophiles and readily available allylic alcohols undergo in situ retro-Claisen activation to generate an allylic acetate and a carbanion. In the presence of palladium, these reactive intermediates undergo catalytic coupling to form a new C-C bond.
A. J. Grenning, J. A. Tunge, J. Am. Chem. Soc., 2011, 133, 14785-14794.
α-Halonitriles react with alkyllithium, organomagnesium, and lithium dimethylcuprate reagents generating reactive, metalated nitriles. The rapid halogen-metal exchange with alkyllithium and Grignard reagents allows Barbier-type reactions with various electrophiles.
F. F. Fleming, Z. Zhang, W. Liu, P. Knochel, J. Org. Chem., 2005, 70, 2200-2005.
Allyl nitroacetates undergo decarboxylative allylation to provide tertiary nitroalkanes in high yield within several minutes under ambient conditions. The preparation of substrate allyl nitroacetates by tandem Knoevenagel/Diels-Alder sequences allows the facile synthesis of relatively complex substrates that undergo diastereoselective decarboxylative allylation.
A. J. Grenning, J.A. Tunge, Org. Lett., 2010, 12, 740-742.
|Enantioselective Allylic Carbon-Carbon Bond Construction|