Diarylmethane products

Scheme 21 Reactivity of 85 in the preparation of diarylmethane products using Suzuki-Miyaura coupling...

Magnesium phenolates react with triethylorthoformate regiospecifically at the ortho position of the phenoxy group (normally phenols give alkyl ethers) giving diarylmethanes. This reaction is complex and the product composition depends on the phenol and the reaction conditions.52... 

A general experimental procedure57 for a diarylmethane leuco compound via a benzotriazole To a stirred solution of the corresponding (benzotriazol-l-yl-methyl)aniline (5 mmol) in methanol (30 ml) under reflux was added a solution of the appropriate aromatic compound (5 mmol) and concentrated hydrochloric acid (1 ml) in water (30 ml). The resulting mixture was heated under reflux followed by the addition of aqueous KOH (1 M, 50ml). The product was isolated by filtration or by extraction with ether, and further purified by recrystallization or by column chromatography. 

It is interesting to consider the factors affecting the product selectivity. Our experimental studies have examined precisely such phenomena. In this article we review the hydrogenolysis of asymmetric diarylmethanes based on our investigations. 

Oxidation of Other Diarylmethanes. Table VII summarizes the products isolated in the oxidation of a number of other diarylmethanes. 

When paraformaldehyde is added to a solution of II in concentrated sulfuric acid at room temperature, a rapid reaction takes place, yielding colorless to orange polymeric compositions depending upon the ratio of reactants and the reaction condition employed (17). It is reasonable to assume that the polymerization of II with formaldehyde proceeds in a fashion similar to that of an activated aromatic ring with formaldehyde to yield as final products the diarylmethane and dimethylene oxy-derivatives, IV and V (Equation 9). 

Reduction of diaryl thioketones with ytterbium metal affords a mixture of the corresponding thiols and diarylmethanes together with products arising from homocoupling reactions (equation 119)433. 

Another example is the photoreaction of tctrazolo[ 1,5- ]pyrimidinc 14 with aromatic compounds in the presence of trifluoroacetic acid (TFA) to give 2-(2-, 3-, and 4-substituted anilino)pyrimidines together with 2-aminopyridine and biphenyl or diarylmethanes. Here the key intermediate is also the 2-pyrimidylnitrenium ion originating from the photochemical decomposition of an imidoyl azide. This ion, depending on the reaction conditions, is present either in the singlet or triplet state and this governs the composition of the products (Scheme 11) <1998JP0478>. 

Anilines are readily oxidized by DIB, being converted either into azo compounds or into other products of condensation, in complex solvent-dependent reactions without much synthetic utility. Better results were obtained in some intramolecular cyclizations of 2,2-diamino-diarylmethanes and 2,2-diamino-diarylsulphones, which afforded the corresponding cyclic azo compounds (diazepines) [50,51], More generally, intramolecular cyclizations of ortho-substituted anilines are known to occur on oxidation of several substrates, according to the following scheme [52] ... 

In 1884, Friedel and Crafts reported that the alkylation of benzene or toluene with dichloromethane in the presence of AlCb avoided the corresponding diarylmethanes, besides other products derived from further alkylation and other transformations. pr ucts from the reaction with benzene are shown... 

The following products of alkylation/condensation were detected diphenyl-methane, methyl-diphenylmethane and xylenes plus minor amounts of styrene, benzofuran, indene, naphthalene, stilbene, anthracene and fluorene. Climent et al. [10] observed the formation of diarylmethanes as one of the primary products of acid-catalyzed condensation of benzaldehyde... 

Reactions of type A (Figure 10.14) involve a carbanion, originating from an ionized phenol structure in lignin, and a quinone methide. The anion can be located either in the aromatic ring or, in some cases, in the side chain of a conjugated aromatic system. Normally, the resulting product will be a substituted diarylmethane structure, but... 

Another unexpected hydrogenolysis reaction was discovered by Lautens while attempting to expand the scope of the cvf/to-alkylation/dircct arylation of thiophenes. When benzyl chlorides were used as alkylating agents, significant amounts of the orffto-benzylation/hydrogenolysis product were obtained. An optimization of the reaction conditions led to an efficient synthesis of diarylmethanes (Scheme 41) [92], This reaction is unique compared to the aforementioned... 

A A -Dialkylarylamines react under classical conditions at C-4 if that position is unsubstituted. For example, A. )V-dimethylaniline reacts with formaldehyde and dimethylamine to afford 4-)V, A -dimethyl-amino-A, Af-dimethylbenzylamine in 82% yield (equation 20). Under acidic conditions fragmentation of the initial product can occur, leading to the formation of diarylmethanes. In the reaction of A A -dimethy-laniline with formaldehyde and pyrrolidine the best yield of the Mannich base (44%) is obtained in the presence of 1.5 mol equiv. of acetic acid with 4.0 mol equiv. the yield is only 7%. The reaction of N-methylenemorpholinium chloride with 4-A -morpholinylmethyl-)V,A -dimethylaniline results in the introduction of a second A -morpholinylmethyl residue at the 2-position, but with other iminium chlorides quaternary salts are formed by reaction with the nitrogen of the 4-dialkylaminomethyl group. There is dso a brief report of the use of the mixed A. Af-dialkylmethyleneiminium salt, A -f-butyl-A -methyl-methyleneiminium perchlorate, with A. Af-dimethylaniline. °... 

Benzo[h] thiophene undergoes selective Rieche formylation (65%) in the 3-position with dichloromethyl butyl ether and TiCl4.508 2-Bromo- and 3-methylbenzo[h]thiophene are similarly formylated in the vacant thiophene position.345 508 The diarylmethane compounds 121 (Ar = thiophene, benzo-[h]thiophene, or benzene) undergo Rieche formylation, but the resulting aldehyde cyclizes under the conditions of the reaction, to give the annelated products 122.509... 

An intramolecular Friedel-Crafts reaction of a diene and an electron-rich aromatic moiety, promoted by BF3-Ft20, was used in the late stage construction of cyclohexyl ring in an approach to the marine natural product pseudopterosin aglycone. In a somewhat related transformation, it has been demonstrated that aromatics can be converted into the corresponding diarylmethane derivative on exposure to a-methoxyacetic acid in the presence of trifluoroacetic anhydride (TFAA) and BF3-Ft20 (eq 49). ... 

Specifically, diphenylmethane was prepared in >90% yield by the reaction of either Ph4Sn or Ph3SnMe with BrCH2Ph in the presence of PhCH2Pd(PPh3)2Cl.f The synthesis of polychlorinated diarylmethanes shown in Scheme 26 is noteworthy despite the modest product yields.f Most of the other currently known examples of Pd-catalyzed aryl-benzyl coupling pertain to the synthesis of heteroarenes (Scheme 27). 

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