Synthesis of oxindoles
A highly regioselective palladium-catalyzed cyclization converts α-chloroacetanilides to oxindoles in good to excellent yields with high functional group compatibility using 2-(di-tert-butylphosphino)biphenyl as ligand and triethylamine as a stoichiometric base.
E. J. Hennessy, S. L. Buchwald, J. Am. Chem. Soc., 2003, 125, 12084-12085.
A catalyst generated from Pd(dba)2 and a bulky electron-rich phosphine ligand is effective for the α-arylation of oxindoles. Generation of the potassium-enolates of a range of oxindoles enables the coupling with aryl chlorides, bromides, and triflates.
M. J. Durbin, M. C. Willis, Org. Lett., 2008, 10, 1413-1415.
A Rh-catalyzed domino conjugate addition-arylation sequence enables the synthesis of 3-substituted oxindole derivatives in good yields via an intramolecular oxidative addition of a rhodium enolate.
Y. J. Jang, H. Yoon, M. Lautens, Org. Lett., 2015, 17, 3895-3897.
A new platinum-catalyzed oxoarylation of ynamides with nitrones gives oxoarylation products. A cascade sequences via NaBH3CN reduction of in situ formed oxoarylation products allows the synthesis of indolin-2-ones.
S. Bhunia, C.-J. Chang, R.-S. Liu, Org. Lett., 2012, 14, 5522-5525.
A nickel-catalyzed aromatic C-H alkylation with tertiary or secondary alkyl-Br bonds enables the construction of indolones. The reaction tolerates various functional groups. Moreover, challenging secondary alkyl bromides can also be transformed. Radical trapping and photocatalysis conditions exhibited that a radical process is involved in this aromatic C-H alkylation.
C. Liu, D. Liu, W. Zhang, L. Zhou, A. Lei, Org. Lett., 2013, 15, 6166-6169.
Chiral N-heterocyclic carbene (NHC) ligands having a 2,2′-bisquinoline-based C2 symmetric skeleton exhibited good enantioselectivity in palladium-catalyzed intramolecular α-arylation of amides to give 3,3-disubsituted oxindoles.
L. Liu, N. Ishida, S. Ashida, M. Murakami, Org. Lett., 2011, 13, 1666-1669.
Potassium tert-butoxide-mediated intramolecular α-arylations of fluoro- and chloro-substituted anilides provide oxindoles in DMF at 80°C. Diversely substituted products have been obtained in good yields.
A. Beyer, J. Buendia, C. Bolm, Org. Lett., 2012, 14, 3948-3951.
A palladium catalyst derived from an air-stable secondary phosphine oxide enabled efficient intramolecular α-arylations of amides with aryl chlorides to give various substituted oxindoles and azaoxindoles in good yield.
L. Ackermann, R. Vicente, N. Hofmann, Org. Lett., 2009, 11, 4274-4276.
An efficient palladium-catalyzed alkylarylation of acrylamides with unactivated alkyl halides offers broad substrate scope and excellent functional group tolerance. In addition to alkyl halides, fluoroalkyl halides and benzyl bromides also participated well in this transformation. A radical pathway is probably involved in the cyclization process.
H. Wang, L.-N. Guo, X.-H. Duan, J. Org. Chem., 2016, 81, 860-867.
A nickel-catalyzed domino Heck cyclization/Suzuki coupling reaction enables the synthesis of 3,3-disubstituted oxindoles bearing quaternary all-carbon centers. A wide range of electrophiles, such as aryl iodides, bromides, triflates, chlorides, and cheap aryl esters can be employed. This practical and sustainable reaction offers good yields and broad scope.
Y. Li, K. Wang, Y. Ping, Y. Wang, W. Kong, Org. Lett., 2018, 20, 921-924.
A facile method enables the construction of quaternary 3,3-disubstituted 2-oxindoles from 2-substituted indoles without a catalyst under mild conditions via an iminium-intermediate-triggered 1,2-rearrangement.
X. Jiang, J. Yang, F. Zhang, P. Yu, P. Yi, Y. Sun, Y. Wang, Org. Lett., 2016, 18, 3154-3157.
3-Monofunctionalized 2-oxindoles were conveniently synthesized from reactions between an anilide and phenyliodine(III) diacetate (PIDA) through hypervalent iodine mediated C(sp2)–C(sp2) bond formation followed by a subsequent deacylation. This metal-free method provides direct access to interesting oxindole intermediates, as exemplified by the total synthesis of horsfiline.
J. Lv, D. Zhang-Negrerie, J. Deng, Y. Du, K. Zhao, J. Org. Chem., 2014, 79, 1111-1119.
A cross-dehydrogenative coupling enable a low-temperature procedure for the synthesis of 3,3-disubstituted 2-oxindoles. The use of a strong, nonreversible base effects a dramatic drop in reaction temperature. With iodine as an "oxidant", new evidence suggests that this transformation may occur via a transiently stable iodinated intermediate rather than by direct single-electron oxidation.
J. R. Donald, R. J. K. Taylor, W. F. Petersn, J. Org. Chem., 2017, 82, 11288-11294.
Highly efficient conditions for the preparation of 3,3-disubstituted oxindoles by a formal C-H, Ar-H coupling of anilides have been identified using catalytic Cu(OAc)2•H2O with atmospheric oxygen as the reoxidant in mesitylene or toluene as solvent; no additional base is required.
J. E. M. N. Klein, A. Perry, D. S. Pugh, R. J. K. Taylor, Org. Lett., 2010, 12, 3446-3449.
A catalyst-free halogenative cyclization of N-aryl diazoamides with N-halosuccinimides (NXS) provides 3-halooxindoles in good yields through a carbene-free mechanism under mild and catalyst-free conditions. This transformation is proposed to proceed through diazonium ion formation followed by intramolecular Friedel-Crafts alkylation.
C. Ma, D. Xing, W. Hu, Org. Lett., 2016, 18, 3134-3137.
Peroxy trichloroacetimidic acid, in situ generated from aqueous hydrogen peroxide and trichloroacetonitrile, acts as a competent electrophilic oxygenating agent for a direct enantioselective α-hydroxylation of oxindoles in the presence of a chiral 1,2,3-triazolium salt as a phase-transfer catalyst.
K. Ohmatsu, Y. Ando, T. Ooi, Synlett, 2017, 28, 1291-1294.
In a Pd-catalyzed domino cyclization and carboxylation reaction for synthesis of a variety of carboxylic acids, chloroform was used as convenient and safe carbon monoxide source. Heck cyclization leads in situ to a neopentylpalladium species, that can efficiently be trapped by dichlorocarbene to form a series of carboxylic acids.
X. Liu, B. Li, Z. Gu, J. Org. Chem., 2015, 80, 7547-7554.
A small library of α,β-unsaturated oxindoles was prepared by an efficient microwave-assisted one-pot sequence comprising an aromatic substitution followed by an ionic Horner-Wadsworth-Emmons olefination.
A. Teichert, K. Jantos, K. Harms, A. Studer, Org. Lett., 2004, 6, 3477-3480.
A [3 + 2] cycloadition of in situ generated arynes and (putative) aza-oxyallyl cations enables an unprecedented metal- and oxidant-free synthesis of N-alkoxy oxindoles. The versatility of this approach was demonstrated through valuable synthetic transformations.
R. Singh, K. Nagesh, D. Yugandhar, A. V. G. Prasanthi, Org. Lett., 2018, 20, 4848-4853.