Diarylmethane derivatives

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). ... 

In this field, Yoshida et al. have also made interesting contributions describing some insertion reaction of aiynes into C—C a-bonds. IMth /i-toluenesulfonylacetonitrile or malononitrile two equivalents of the corresponding arynes react with the starting material. The overall process, which takes place through an initial C—C a-bond insertion, involves the formation of three C—C and one C—H bonds, and affords diverse diarylmethane derivatives 82 in a straightforward manner (Schane 12.43) [72]. 

Encouraged by these results, the reaction of benzylic alkoxides with dichloroborane was examined. These reactions provide an alternative route to diarylmethane derivatives (Schane 23.77). The deoxygenation of alkoxides using dichloroborane provides useful evidence for understanding the importance of Lewis acidity in previously reported deoxygenation methods operating through alkoxide intermediates. ... 

Benzophenones are produced by the oxidation of diarylmethanes under basic conditions [6-9], The initial step requires a strongly basic medium to ionize the methane and the more lipophilic quaternary ammonium catalysts are preferred (Aliquat and tetra-n-octylammonium bromide are better catalysts than tetra-n-butyl-ammonium bromide). The oxidation and oxidative dehydrogenation of partially reduced arenes to oxo derivatives in a manner similar to that used for the oxidation of diarylmethanes has been reported, e.g. fluorene is converted into fluorenone (100%), and 9,10-dihydroanthracene and l,4,4a,9a-tetrahydroanthraquinone into anthraquinone (75% and 100%, respectively) [6]. 

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). 

Substituted diarylmethanes have been prepared from formaldehyde and a variety of its derivatives. Sulfuric acid is a common catalyst. The procedure described is based on the general method of Gordon, May, and Lee. Formic acid is preferable to sulfuric acid as a catalyst because it is capable of acting as a solvent as well, thus eliminating troublesome emulsions. Side reactions such as sulfonation are avoided. 

Negishi, E., King, A. O., Okukado, N. Selective carbon-carbon bond formation via transition metal catalysis. 3. A highly selective synthesis of unsymmetrical biaryls and diarylmethanes by the nickel- or palladium-catalyzed reaction of aryl- and benzylzinc derivatives with aryl halides. J. Org. Chem. 1977,42, 1821-1823. 

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 intermolecular Friedel-Crafts alkylation with benzyUc and aUyUc halides occurs at room temperature in CH2CI2. Diarylmethanes are also obtained in moderate yields from arenes and benzyl alcohols on heating the mixtures with InCls 4H2O and acetylacetone at 120°. l-VinyltetraUn and 4-vinyltetrahydrDisoquinoline derivatives are readily formed by an intramolecular aUylation. ... 

Such reactions, which will not be discussed further here, include the formation of diarylmethanes from an aldehyde and two molecules of an aromatic hydrocarbon, of triphenylmethane derivatives from an aldehyde and two molecules of an aromatic amine, and of phthaleins from phthalic anhydride and two molecules of phenol or resorcinol. 

Unsymmetrical biaryh and diarylmethanes. Negishi et al have used a nickel-(0) complex or a palladium(0) complex as catalyst for the cross-coupling of aryl-or benzylzinc halides with aryl halides at room temperature to form biaryls or diarylmethanes. The zinc derivatives are prepared by reaction of aryl- or benzyl-lithium with zinc chloride or bromide. 

Anodic oxidation of dithioketals with /tara-iodoanisole in acetonitrile in the presence of EtsN 3HF as an electrolyte forms gem-difluoro derivatives of diarylmethane (94JOC7190) (Scheme 50). (Difluoroiodo)arenes possess a high fluorinating abihty. These substances need not be isolated pure one can employ their solutions in acetonitrile. 

Another improvement of the DPM rigidity and preorganization without alteration of the substitution pattern is the back-stabilization of the gable conformation. The 1.1-diphenylcyclopropane derivatives invariably show preference for the gable conformation, as revealed from x-ray data. Also, in diarylmethane-bridged fullerenes, the gable disposition was described as the most stable conformation. However, no experimental rotational barriers were reported until now. 

This reaction was initially studied by von Baeyer in 1872. It is an acid-catalyzed condensation of aromatic compounds with formaldehyde or formaldehyde derivatives. In normal conditions, the reactive benzene derivatives such as phenols and arylamines are applied to condense with formaldehyde however, a small number of less-reactive aromatics have also been used in this reaction, including benzene, toluene, benzyl chloride,biphenyl, iodobenzene, naphthalene, and mesitylene. Although no yields were given in the early studies, it is reasonable to obtain 70-80% yield for this type of reaction. Many other reactions have been developed to synthesize diarylmethanes, including Katritzky s benzotriazole method, Kochi s dealkylative coupling," Fukuzaw s 1,3-propandiol method, and the reduction method. In general, the condensation occurs at the /tflra-position of substituted aromatics. 

Trimethylaluminum exhaustively methylates O-functions and thus converts tert. alcohols to alkanes, ketones to gem-dimethyl compounds, and carboxylic acids to terUhuiyX derivatives . AgC104-SnCl4 gives high yields of diarylmethanes by benzylation of arenes, e. g. with benzyl alcohol . 

The alkylation of 2-arylpyridine and 2-aryloxazoline derivatives with benzylhalides leads to regioselective ort/io-monoakylations under similar conditions and to the formation of diarylmethane compounds. However this reaction revealed the surprising higher efficiency of benzylchlorides compared to benzylbromides [(Eq. 35)] [110]. 

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