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