1,1-Diarylalkanes, formation

There is ample evidence that the formation of excimers and exciplexes in covalently linked, a, co-diarylalkanes is optimum for a chain length comprising three methylene groups, since this configuration allows a face-to-face sandwich-type structure to be achieved without imposing severe entropic penalties [58, 59], A two-carbon atom chain is rather too short for optimal exciplex formation, but it facilitates TB mediated ET from an aW-trans conformation, as shown in Figure 16b. 

Instead of nucleophiles such as H2O, MeOH, RNH2 and halide ions, both the aryl group and olefinic double bond will react with an electrogenerated phenoxonium ion to give carbon-carbon coupled products. In particular, electrooxidative coupling reactions of a,ft)-diarylalkanes leading to cyclic diaryl ethers have been known to take place in a radical or cationic manner depending on the oxidation potential, the nature and location of substituents, the solvent systems and other factors, as cited in many books Electrochemical carbon-carbon bond formations will be described here. 

A soln. of startg. benzyl bromide in THF added slowly to cut zinc foil activated with 1,2-dibromoethane at 0°, after stirring for 2-3 h at 5° the soln. added to CuCN and LiCl in THF at —70°, warmed to —20° for 5 min, re-cooled to —70°, a soln. of allyl bromide in THF added, the mixture warmed slowly to 0°, and worked up after 5 min - product. Y 96%. The method is mild, and formation of 1,2-diarylalkane crosscoupling products minimal functional groups such as esters, nitriles, halides, and ketones are tolerated. F.e. and electrophiles s. S.C. Berk et al., J. Org. Chem. 53, 5789-91 (1988). 

Zachariasse, K.A. Intramolecular excimer formation with diarylalkanes as a microfluidity probe for sodium dodecyl sulfate micelles. Chem. Phys. Lett. 1978, 57(3), 429 32. 

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