The effects of space formed by host molecules in inclusion compounds on the homogeneity/heterogeneity of the photoreaction in the solid state

Two inclusion compounds that contain a light-stable host molecule and a light-sensitive guest molecule have been crystallized, that is, 4,5-bis(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxolane as the host molecule with tropolone methyl ether as the guest molecule and 2,3-bis(hydroxydiphenylmethyl)-1,4-dioxaspiro[4.5]decane as the host molecule with 4-(oxophenylacetyl)morpholine as the guest molecule. The two inclusion compounds undergo photochemical ring-closure reactions. However, while the first reacts by a heterogeneous process, the second undergoes a homogeneous photoreaction. The X-ray crystal structure of the two compounds clearly demonstrate that when the space required by the guest molecule to undergo the photoreaction fits the space provided by the host molecule, the reaction is homogeneous; when the space required by the guest is larger than that provided by the host molecule, the photoreaction is heterogeneous. Since the photochemical reaction of the inclusion compound with tropolone methyl ether as the guest is heterogeneous it could not be followed by single-crystal X-ray diffraction. The product of the photochemical reaction is 1-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one. The photochemical reaction of the second compound was followed by single-crystal X-ray diffraction and the crystal structure shows that the product is tetrahydro-2-phenyloxazolo[2,3-c] [ 1,4]oxazine-3(2H)-one, and not the beta-lactam system obtained in similar reactions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)