A multistep photoreaction of aromatic aldehydes with heteroaromatics in the solid state

Mixed crystals, prepared by resolidification of the melt of a mixture of 5-formyl-1,3-dimethyluracil (1a) and antipyrine (7) crystals (molar ratio, 1:2.5), and irradiated with a high-pressure mercury lamp under nitrogen, gave a photocondensation product 8a, as in the previously reported solid state photoreaction between 1a and indole. Similarly, irradiation of mixed crystals of substituted benzaldehydes and indole gave the corresponding photocondensation product 3. A mechanism involving an oxetane intermediate 4 was proposed for the formation of 3. The nature of the starting mixed crystals was examined by powder X-ray diffractometry.