The prepration of some unsymmetrical ortho substituted ̲o-dibenzoylbenzenes and 1,3-diphenylisobenzofurans

Abstract

A review of the more important methods of synthesis of 1,3-diarylisobenzofurans (III) and o-diaroylbenzenes (II) was made. These were compared with the possibilities involved in the type of synthesis in which substituted o-benzylbenzophenones (I) are oxidized to o-diaroylbenzenes (II) and subsequently reduced to 1,3-diarylisobenzofurans (III). It is seen that this latter method affords a greater variety of substituents for these types of compounds than the other methods. The possible orientations of substituents are also greater.

Two o-benzylbenzophenones (I), 2’-methyl-2-benzylbenzophenone (LIII) and 2'-methoxy-2-benzylbenzophenone (LVI), were prepared by the action of the appropriate Grignard reagent on o-benzylbenzonitrile (LII) and subsequent hydrolysis of the intermediate ketimine. These were oxidized to the corresponding o-dibenzoylbenzenes (II), 2’-methyl-2-benzoy1 benzophenone (LIV), and 2'-methoxy-2- benzoylbenzophenone (LVII), by the use of sodium dichromate and sulfuric acid, Reduction of these with zinc dust in acetic acid gave the corresponding 1,3-diarylisobenzofurans (III), 1-(2‘-methylpheny1)-3-phenylisobenzofuran (LV) and 1-2" -methoxyphenyl)-3-phenyl isobenzofuran (LVIII). Attempts were made to prepare 2'-chloro-2-benzylbenzophenone (I; Reo-Cl and R'=R) by the same method as that in the above-mentioned paragraph. None of the ketone could be obtained. A small amount of a hydrocarbon was obtained in one case which was analyzed as C₂₀H₁₄.

The action of the Grignard reagent of 4-iodo-1, 3-dimethylbenzene on o-chlorobenzaldehyde gave 2-chloro-2', 4'-dimethylbenzohydrol (LI).

New compounds synthesized are 2‘-methy1-2~benzoylbenzophenone (LIV), 2'-methoxy-2-benzoyl benzophenone (LVII), 1-(2'-methylphenyl)-3-phenylisobenzofuran (LV), 1-(2'-methoxyphenyl1)-3-phenylisobenzofuran (LVIII), and 2-chloro-2! ,4'-dimethylbenzohydrol (LI).