A specific intramolecular interaction in a bis(2-thienyl)maleimide derivative

Abstract

3,4 Bis(4 ethoxycarbonyl 3 hydroxy 5 methyl 2 thienyl) 1 phenyl 1H pyrrole 2,5 dione shows no photochromism in the crystalline state, despite its typical "photochromic" structure (X ray diffraction data): the anti parallel orientation of the thienyl fragments relative to the plane of pyrrole 2,5 dione and a short distance between potential reactive sites (C(3´)...C(3´A), 3.27 Å). The absence of photochromism was explained by a specific attractive interaction between the O atoms of the maleimide ring and the thiophene S atoms, which can preclude UV induced photocyclization.

Photostability and Antiproliferative Activity of Furan Analogues of Combretastatin A-4

“…It showed that the distance between these atoms did not exceed 2.7 Å, which is less than the sum of the van der Waals radii of these atoms (Scheme A). We propose that the Z stabilization of 2j arises in part from orbital-driven “attractive nonbonded interactions.” − These interactions are most likely driven by HOMO–LUMO and Coulomb interactions, and the sulfur atom acts as a Lewis acid despite its electronegativity. The sulfur atom acts like an “electrophile” as it approaches the electronegative oxygen atom, forming a favorable interaction between the n O HOMO and σ* S LUMO. − …”