The preparation of polynuclear compounds containing the thiophene ring system
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The process of C. K. Bradsher for preparing mesosubstituted anthracene and 1,2-benzanthracene derivatives has been widely extended. The purpose of this research was to extend this process to the thiophene series, in addition to continuing some work on the 9-(dimethyl)- phenylanthracene series and some newly developed l,2-dimethyl-10-phenyl)-anthracene series. 2'-Thienyl-2-benzylbenzophenone was prepared and cyclized to 9-(2-thienyl)-anthracene by the conventional methods in good yields. 3'-Thienyl-2-benzylbenzophenone was prepared in a different way, indirect and tedious. Thiophene was iodinated to tetraiodothiophene and tetraiodothiophene was reduced with aluminum-amalgam to 3-iodothiophene. 3-Thienylmagnesiumiodide was prepared by the entrainment technique and condensed with 2-cyanodiphenylmethane to 3'-thienyl-2-benzylbenzophenone. This ketone was cyclized to 9-(3'-thienyl)-anthracene by the standard acid mixture. 2-(1-Naphthylmethyl)-phenyl-2-thienylketimine formed from the condensation between 2-(1'-naphthylmethyl)- benzonitrile and 2-thienylmagnesiumbromide resisted hydrolysis to the corresponding ketone but cyclized quantitatively to 10-(2-thienyl)-l,2-benzanthracene. Following the classical Bradsher process, the reaction between 2-thienylmagnesiumbromide and o-chlorobenzaldehyde was unsuccessful because the hydrol formed was so reactive that it polymerized rapidly and ended up with tars. A cross-condensation reaction between 2-ethynylmagnesium bromide and o-chlorobenzylchloride was utilized to give the expected 2-(2'-chlorobenzyl)- thiophene in one step. This new procedure has been widely extended to the other series. It is preferred to. the conventional Bradsher process and the Friedel-Crafts method in terms of time, chemicals, and unequivocal products formed. 2-(2'-Chlorobenzyl)-thiophene so formed by the new procedure was converted by von Braun reaction to the corresponding nitrile and the nitrile was allowed to react with phenylmagnesiumbromide to give 2-(2-thienylmethyl)-benzophenone. The above ketone was cyclized almost quantitatively to 4-phenyl-thiophanthrene. The thiophene-containing ketones prepared in this research are very viscous oils. In order to have crystalline derivatives for identification purposes these ketones were oxidized to the corresponding diketones. 2-Thienyl-2-benzylbenzophenone and 2-(2'-thienylmethyl)- benzophenone gave the identical diketone, 2-benzoyl-2'- thienyl-benzophenone. 3 1 -Thienyl-2-benzylbenzophenone was oxidized to anthraquinone by using 25% sulfuric .acid, acetic acid and sodium dichromate. The formation of anthraquinone indicates that the monoketone cyclized first and then split off the thiophene ring. Apparently, the 3-thienyl group is more susceptible to oxidation than the 2’-thienyl group. A study of the oxidation of anthracene derivatives for structure proof was made using 9-phenylanthracene as a model compound. It was oxidized to 10-phenyl-10-hydroxyanthrone which resisted further oxidation to anthraquinone. It is obvious that the tertiary alcohol system stabilized the phenyl ring. In continuing the work on the 9-(dimethyl)-phenylanthracene series, the yields of three ketimine salts and one ketone were improved. Satisfactory analytical data was obtained for 2’,6’-dimethyl-2-benzylbenzophenone. In an attempt to overcome the steric effects offered by 2,6-ortho groups, 2-(2',3'-dimethylbenzyl)-benzonitrile was prepared. The starting material for this series, l-bromo-2,3-dimethylbenzene has been prepared in 47% yield by diazotization in comparison with the previous yield of 30%.
- Doctoral Dissertations