Question

Problem 9 (10 pts) Suggest a reasonable synthetic strategy to carry out the following transformation.

Answer 1

TfOH Catalytic-Activity of different Acyl Donors and Acyl Acceptors

The product 1,7-bis(4-bromophenyl)heptan-4-one from methyl 4-(4-bromophenyl)butanoate can be synthesize by intermolecular C-acylation. It is the type of addition of acyl groups to aromatic-derivatives, which is directed by an activator. Conventional acylation comprises the usages of simple arenes of both electron-rich/electron-poor such as benzene, xylene, toluene; they act as acyl acceptors, and typical acyl donors like carboxylic acid, carboxylic anhydride, acyl chloride, and esters. The Trifluoromethanesulfonic Acid (TfOH) catalytic strategy has made the exploration of various acyl donors, which are more feasible for C-acylation; hence the number of potential donors for this reaction increases. Aromatic compounds on direct C-acylation of using benzoic acid esters are found to extend theses types of exploration series.

For example

One strategy : it is found as, excess TfOH (5 equiv.) at 85 °C, has been utilized for the direct C-acylation of methyl benzoate (2 equiv.) as well as aromatic derivatives, hence synthesizing the derivatives of benzophenone. In this reaction, it is not observed further electrophilic reaction of benzophenones with the aromatics.

For example

Reference,

Tachrim, Z., Wang, L., Murai, Y., Yoshida, T., Kurokawa, N., Ohashi, F., … Hashimoto, M. (2017). Trifluoromethanesulfonic Acid as Acylation Catalyst: Special Feature for C- and/or O-Acylation Reactions. Catalysts, 7(12), 40. doi:10.3390/catal7020040