Compelled orientational control of the solid-state photodimerization of trans-cinnamamides: Dicarboxylic acid as a non-covalent linker

The 2:1 hydrogen-bonded cocrystals 1a.ox, 1a.su, 1a.pht, 1a.fu, 1b.ox, 1c.ox, 1d.ox between trans-cinnamamides (la-ld) and dicarboxylic acids (ox, su, gl, fu, pht) were prepared and characterized by IR and powder X-ray techniques. The crystal structures of la pht, la ox and la fu were solved by single crystal X-ray diffraction. Phthalic acid (pht) caused beta-type photodimerization of trans-cinnamamide (la) in the cocrystal and functioned as a non-covalent licker like gauche 1,2-diamines in photodimerization of trans-cinnamic acids. Oxalic acid (ox) enforced la to take a bilayer structure that is suitable for beta-type photodimerization. In the case of fumaric acid (fu), cross photodimerization with la occurred to give a cycloadduct 4. For the cocrystals la pht and la fu, pedal-like motion was assumed to occur prior to the dimerization. (C) 2000 Elsevier Science Ltd. All rights reserved.