Benzylation, synthesis of diarylmethanes
A metal-free carbon-carbon bond-forming coupling between tosylhydrazones and boronic acids is very general and functional-group tolerant. As the required tosylhydrazones are easily generated from carbonyl compounds, it can be seen as a reductive coupling of carbonyls, a process of high synthetic relevance that requires several steps using other methodologies.
J. Barluenga, M. Tomás-Gamasa, F. Aznar, C. Valdés, Nat. Chem., 2009, 1, 494-499.
A novel InCl3/SiO2-catalyzed hydroarylation of various styrenes with arenes can be carried out under solvent-free conditions to afford a series of 1,1-diarylalkanes in high yields and with good regioselectivities. The catalyst can be reused six times without obvious loss of catalytic activity.
G. Sun, H. Sun, Z. Wang, M.-M. Zhou, Synlett, 2008, 1096-1100.
A highly efficient secondary benzylation procedure of nucleophiles (arenes, heteroarenes, alcohols, thiols, amides) with benzylic alcohols afforded the corresponding benzylated products in moderate to excellent yields in the presence of a high-valent heterobimetallic complex [Ir2(COD)2(SnCl3)2(Cl)2(μ-Cl)2] as the catalyst.
S. Podder, J. Choudhury, S. Roy, J. Org. Chem., 2007, 72, 3129-3132.
The reaction of benzylic chlorides with Al-powder in the presence of InCl3 as catalyst provides various functionalized benzylic aluminum sesquichlorides under mild conditions. These organometallics reacted smoothly in Pd-catalyzed cross-couplings, or Cu-mediated acylations, allylations, or 1,4-addition reactions. Substrates prone to Wurtz coupling can be converted to benzylic zinc compounds first.
T. D. Blümke, K. Gross, K. Karaghiosoff, P. Knochel, Org. Lett., 2011, 13, 6440-6443.
Diarylmethanes can be accessed efficiently by Suzuki-Miyaura cross-couplings of arylboronic acids with benzyl halides mediated by trans-PdBr(N-Succ)(PPh3)2. The methodology can be applied to the synthesis of heteroaryl analogues.
I. J. S. Fairlamb, P. Schnal, R. J. K. Taylor, Synthesis, 2009, 508-510.
The palladium-catalyzed cross-coupling of various benzylic carbonates with arylboronic acids gave the corresponding diarylmethanes in high yields. The catalyst is generated in situ from [Pd(η3-C3H5)Cl]2 and 1,5-bis(diphenylphosphino)pentane (dpppe).
R. Kuwano, M. Yokogi, Org. Lett., 2005, 7, 945-947.
A cross-coupling reaction of various aryl, heteroaryl, and benzyl chlorides with ArMgX is catalyzed by nickel in the presence of a bidentate phosphine ligand. The ligand is stable in air and forms a stable complex in situ upon reaction with Ni(CH3CN)2Cl2.
R. Ghosh, A. Sarkar, J. Org. Chem., 2010, 75, 8283-8386.
The use of the Xantphos ligand in a mild palladium-catalyzed Kumada-Corriu reaction of secondary benzylic bromides with aryl and alkenyl Grignard reagents minimizes the undesired β-elimination pathway. The corresponding cross-coupling products can be isolated in good yields with inversion of the configuration.
A. López-Pérez, J. Adrio, J. C. Carretero, Org. Lett., 2009, 11, 5514-5517.
An efficient Hiyama coupling reaction between benzylic halides and aryltrialkoxysilanes using Pd nanoparticles allows the synthesis of a diverse range of diarylmethanes which are ubiquitous units of natural products and pharmaceuticals.
D. Srimani, A. Bej, A. Sarkar, J. Org. Chem., 2010, 75, 4296-4299.
Suzuki-Miyaura cross-coupling of benzylic phosphates with arylboronic acids using a simple catalytic system of palladium(II) acetate and triphenylphosphine with either potassium phosphate or potassium carbonate as the base and toluene as the solvent at 90°C allows the preparation of a series of structurally diverse diarylmethanes.
M. McLaughlin, Org. Lett., 2005, 7, 4875-4878.
Coupling of sterically hindered aryl and activated alkyl chlorides bearing β-hydrogens has been successfully achieved by using N-heterocyclic carbene (NHC)Pd-carboxylate complexes as catalysts.
R. Singh, M. S. Viciu, N. Kramareva, O. Navarro, S. P. Nolan, Org. Lett., 2005, 7, 1829-1832.
A new, reusable Pd/MgLa mixed oxide catalyst has been applied successfully in the Suzuki-Miyaura cross-coupling reaction of aryl halides as well as benzylic bromide with boronic acids in ethanol. The catalyst is air stable, can be stored and handled under an ambient atmosphere and after the reaction it can be recovered by simple filtration and reused without significant loss of activity.
A. Cwik, Z. Hell, F. Figueras, Org. Biomol. Chem., 2005, 3, 4307-4309.
Palladium catalyzed Suzuki-Miyaura coupling with aryl chlorides using a bulky phenanthryl N-heterocyclic carbene ligand
C. Song, Y. Ma, Q. Chai, C. Ma, W. Jiang, M. B. Andrus, Tetrahedron, 2005, 61, 7438-7446.
A combination of copper chloride, triethyl phosphite, and tetrabutylammonium iodide is a very efficient catalytic system for cross-coupling reaction of arylmagnesium halides with benzylic phosphates.
C. C. Kofink, P. Knochel, Org. Lett., 2006, 8, 4121-4124.
A hybrid catalyst of iron oxide nanoparticles on carboxy-functionalized graphite demonstrated superior catalytic activity towards the alkylation of arenes with alkyl halides in contrast to commercial graphite or unsupported iron oxide nanoparticles. The catalyst can be reused up to five times with a minimal loss of catalytic activity.
V. Rajpara, S. Banerjee, G. Sereda, Synthesis, 2010, 2835-2840.
Suzuki-Miyaura coupling of diarylmethyl carbonates with arylboronic acids gives various triarylmethanes in the presence of [Pd(η3-C3H5)Cl]2−DPPPent (1,5-bis(diphenylphosphino)pentane) as catalyst.
J.-Y. Yu, R. Kuwano, Org. Lett., 2008, 10, 973-976.
Sm(OTf)3 is an effective catalysts for a versatile and efficient halogen-promoted highly regio- and stereoselective Friedel-Crafts (F-C) alkylation of electron-rich arenes with alkenes and α,β-unsaturated carbonyl compounds in the presence of NBS or I2 as halogen sources.
S. Haira, B. Maji, S. Bar, Org. Lett., 2007, 9, 2783-2786.
The superacid-catalyzed reaction of various olefinic amines and related compounds with benzene gives addition products in good yields. The formation of reactive, dicationic electrophiles is proposed.
Y. Zhang, A. McElrea, G. V. Sanchez, Jr., D. Do, A. Gomez, S. L . Aguirre, R. Rendy, D. A. Klumpp, J. Org. Chem., 2003, 68, 5119-5122.
The reaction of different functionalised organolithium compounds prepared by DTBB-catalysed lithiation of isochromane, phthalane, 2,3-dihydrobenzofuran and 1-chloro-3,3-diethoxypropane with an equimolecular amount of zinc bromide, followed by reaction with an aryl or an alkenyl bromide in the presence of a palladium catalyst gives the expected cross-coupling products.
M. Yus, J. Gomis, Eur. J. Org. Chem., 2002, 1989-1995.