| Popis: |
The trans–cis isomerisation of trans-α-benzyl-α′-benzylidenesuccinic acid and related compounds, photochemically and through base-catalysed hydrogen-migration reactions of the αα′-dibenzylmaleic anhydride and dimethyl αα′-dibenzylmaleate intermediates is described. The α-arylidene and αα′-diarylidenesuccinic acids, obtained from the Stobbe condensation of aldehydes with succinic esters, have a trans-arrangement of aryl and carboxy-groups. Structural assignments are based on n.m.r. studies of the methyl esters of these acids, which show that the olefinic proton in the trans-arrangement gives a signal at lower field than the corresponding cis-arrangement owing to the deshielding effect which results from the diamagnetic anisotropy of the methoxycarbonyl group. |
