70430-09-0Relevant articles and documents
Synthesis of Triarylmethanes via Palladium-Catalyzed Suzuki-Miyaura Reactions of Diarylmethyl Esters
Dardir, Amira H.,Casademont-Reig, Irene,Balcells, David,Ellefsen, Jonathan D.,Espinosa, Matthew R.,Hazari, Nilay,Smith, Nicholas E.
supporting information, p. 2332 - 2344 (2021/06/28)
The synthesis of triarylmethanes via Pd-catalyzed Suzuki-Miyaura reactions between diarylmethyl 2,3,4,5,6-pentafluorobenzoates and aryl boronic acids is described. The system operates under mild conditions and has a broad substrate scope, including the coupling of diphenylmethanol derivatives that do not contain extended aromatic substituents. This is significant as these substrates, which result in the types of triarylmethane products that are prevalent in pharmaceuticals, have not previously been compatible with systems for diarylmethyl ester coupling. Furthermore, the reaction can be performed stereospecifically to generate stereoinverted products. On the basis of DFT calculations, it is proposed that the oxidative addition of the diarylmethyl 2,3,4,5,6-pentafluorobenzoate substrate occurs via an SN2 pathway, which results in the inverted products. Mechanistic studies indicate that oxidative addition of the diarylmethyl 2,3,4,5,6-pentafluorobenzoate substrates to (IPr)Pd(0) results in the selective cleavage of the O-C(benzyl) bond in part because of a stabilizing η3-interaction between the benzyl ligand and Pd. This is in contrast to previously described Pd-catalyzed Suzuki-Miyaura reactions involving phenyl esters, which involve selective cleavage of the C(acyl)-O bond, because there is no stabilizing η3-interaction. It is anticipated that this fundamental knowledge will aid the development of new catalytic systems, which use esters as electrophiles in cross-coupling reactions.
Efficient access to triarylmethanes through decarboxylation
Saha, Tiash,Kumar, M. Srinivas Lavanya,Bera, Saurav,Karkara, Bidhu Bhusan,Panda, Gautam
, p. 6966 - 6971 (2017/02/05)
A new synthetic approach has been developed for efficient access to triarylmethanes by palladium catalyzed decarboxylative cross coupling reactions. The reaction features sp2-sp3 coupling where benzoic acids upon decarboxylation reac
A photochemical retro-Friedel-Crafts alkylation. Rapid rearrangement of cyclohexadienyl cations
MacKnight, Earl,McClelland, Robert A.
, p. 2518 - 2527 (2007/10/03)
This paper reports the use of laser flash photolysis (LFP) techniques to show that cyclohexadienyl cations (σ complexes) of the Friedel-Crafts reaction of 1,3-dimethoxybenzene and the diphenylmethyl cation rearrange on the ns time scale without separating the aromatic compound and the electrophile. This is demonstrated through a study of the photochemical behaviour of 2-diphenylmethyl-1,3-dimethoxybenzene (4) in 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP). Derivatives of 1,3-dimethoxybenzene have previously been found to selectively protonate at C2 upon excitation in HFIP, and indeed the principal products with 4 are 1,3-dimethoxybenzene (6) and Ph2CHOCH(CF3)2 (7), the species expected if the cyclohexadienyl cation formed in the C2 protonation cleaved Ph2CH+. These products are, however, accompanied by 4-diphenylmethyl-1,3-dimethoxybenzene (8), a rearranged isomer of 4. A portion of this product is explained by the combination of Ph2CH+ and 1,3-dimethoxybenzene as the latter accumulates during the irradiation. However, 11.5% of 8 is also seen upon extrapolation to zero time. LFP experiments on the ps time scale reveal that the C2 protonated cation, the 1-diphenylmethy 1-2,6-dimethoxybenzenium ion (5), is formed within 100-200 ps, and reacts with k = 9 × 108 s-1, with absorbance for Ph2CH+ growing in as 5 decays. LFP studies on the ns time scale reveal that there is a second quantity of Ph2CH+ that grows in, with k = 5.0 × 105 s-1. The precursor for this has been identified as the 1-diphenylmethyl-2,4-dimethoxybenzenium ion (10), the thermodynamically more stable isomer of 5. A mechanistic model is proposed in which excited 4 is C2 protonated in HFIP with k ≥ 1 × 1010 s-1 to form 5, which loses Ph2CH+ with k = 3 × 108 s-1 in competition with rearrangement to 10 with k = 6 × 108 s-1. The cation 10 serves as the second source of Ph2CH+, losing Ph2CH+ with k = 4 × 105 s-1; in competition 10 is deprotonated by HFIP to give 8 with k = 8 × 104 s-1. The 11.5% of the rearranged 8 that is observed at zero conversion is thus shown to come from an intramolecular pathway in which the key step is the migration of a diphenylmethyl group without separation: 4 → 4* → 5 → 10 → 8.
Triarylcarbenium Salts Highly Reducible by Primary Alcohols
Wada, Masanori,Mishima, Hisashi,Watanabe, Tetsuya,Natsume, Satoko,Konishi, Hideki,et al.
, p. 243 - 249 (2007/10/02)
A series of triarylmethanols bearing o-methoxyl groups (1a: 3COH, 1b: (2-MeOC6H4)2COH, 1c: Ph2COH, 1d: 3COH, 1e: Ph2COH) were prepared.Corresponding carbenium salts, X 2a-c, were isolated by short-period treatments of Ar3COH 1a-c with a slight excess of acid in some bulky alcohols, such as 2-propanol or 2-methyl-1-propanol.The high basicity of 1a-c was explained by through-space interactions of a pair of 2p electrons of an o-methoxyl oxygen with an empty 2p orbital of the resulting carbenium carbon.In ethanol, 1-butanol or 3-methyl-1-butanol, 1c, as well as 2c, was reduced under very mild conditions to triarylmethane, Ar3C-H 3c, and in other bulkier alcohols it was reduced under more forcing conditions.The formations of aldehyde or ketone, the by-product, were confirmed in some cases.Compounds 1a,b,d,e, as well as 2a,b, reacted in analogous manners under more forcing conditions.The reaction rates in several alcohols increased in the order 2a 3-methyl-1-butanol > 1-butanol > 2-propanol > methanol > 2-butanol > 2-methyl-1-propanol.Compounds 2b,c were also reduced in tetrahydrofuran, and formed xanthene derivatives in dimethyl sulfoxide or in water.
