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We are grateful

for the

generous support from

the

National Science Foundation

(

CHE-0910826).

Introduction and History

Attempted Cyclizations of Diphenyl and Triphenylmethane

References

Acknowledgements

Benzyl Group Migrations

(1)

(a)

Baddeley

, G.; Kenner,

J. Chem. Soc.

1935

, 303-9. (b) Nightingale, D. Carton, B. J. Am. Chem. Soc. 1940, 62, 280-3. (c) Norris, J. F.; Vaali, G. T. J. Am. Chem. Soc. 1939, 61, 2131.(2) Allen, C. F. H.; Pingert, F. P. J. Am. Chem. Soc. 1942, 64, 1365.(3) Olah, G. A.; Meyer, M. W., J. Org. Chem. 1962, 27, 3682-3.(4) Ajaz, A.; McLaughlin, E. C.; Skraba, S. L.; Thamatam, R.; Johnson, R. P. J. Org. Chem. 2012, 77, 9487-95.(5) Olah, G. A.; Meyer, M. W.; Overchuk, N. A. J. Org. Chem. 1964, 29, 2313.(6)Scholl, R.; Seer, C.; Weitzenbock, R. Ber. Dtsch. Chem. Ges. 1910, 43, 2202.(7) Blitz, H. Ber. Dtsch. Chem. Ges. 1893, 26, 1960-2.(8) Roberts, R. J. Org. Chem. 1987, 52, 1591-1599(9) McLaughlin, E. Master’s Thesis, 2012.

Benzyl Group Migration and Exchange in

Arenium IonsHilary E. Miller and Richard P. JohnsonUniversity of New Hampshire, Department of Chemistry, Durham, NH

The rearrangement from the

para

to

meta isomer of alkyl benzenes was first reported by Baddeley in the 1930’s.1 Allen and Pingert were the first to study similar rearrangements in terphenyl isomers with AlCl3.2 A 0:64:36 o:m:p ratio was reported by Olah and co-workers who studied the rearrangements of terphenyl isomers upon heating with AlCl3.3 The preference for the meta-substituted isomer corresponds with the formation of the most stable carbocation.4 The rearrangement occurs through the ipso-arenium ion, as shown below.5

It is believed that the AlCl3 catalyst reacts with water to generate AlCl3-OH2 as an acid. Work by Johnson and co-workers here at UNH has shown that terphenyl isomers also rearrange with trifluoromethane sulfonic acid (TfOH) in dichloroethane (DCE).4 These conditions are more reliable than AlCl3 and yield a product distribution that correlates with the results previously published by Olah and co-workers.4

Synthesis of Anthracene

Scholl Reaction

In

1910, Scholl reported the formation of perylene when 1,1’-binaphthyl was heated with AlCl3.6 This type of reaction, featuring the coupling or cyclization of arenes through formation of a C-C bond, is known as the Scholl reaction.

Benzyl Group Fragmentation and Exchange

Ipso-protonation leads to very facile fragmentation of benzyl groups. In benzene-d6, we find rapid exchange, as seen by 1H NMR analysis.

Our attempts to repeat Blitz’s 1893 cyclization of triphenylmethane with aluminum chloride were unsuccessful. Instead, anthracene was observed!

This matches previous work reported by Royston Roberts, who also reported formation of anthracene from

diphenyl

and triphenyl methane with AlCl3.8 A possible mechanism for the reaction is shown below. This mechanism involves interconversion of dibenzylbenzene isomers.

Rearrangement of DibenzylbenzeneOrtho-, meta-, and para- isomers of dibenzylbenzene were synthesized.9

Computational Studies

It was not possible to find a transition state for the benzyl group migration. It is likely that the benzyl group completely dissociates.

In 1893, Blitz synthesized a mixture of

diphenyl

and triphenylmethane from benzene and aluminum chloride refluxed in chloroform.

7

He reported that if the mixture was refluxed for over 4 hours, a third product, 9-phenylfluorene, was observed, presumably from cyclization of triphenylmethane.

In our experiments, attempts to

cyclize diphenyl or triphenylmethane with triflic acid in dichloroethane were unsuccessful. Instead, dibenzylbenzene isomers and triphenylmethanol were observed.

Work is currently in progress to see if the ortho-, meta-, and para- isomers of

dibenzylbenzene

interconvert or rearrange to form anthracene with catalysis by triflic acid or aluminum chloride.