Photochemistry of Compounds Containing CC Double Bonds

Abstract

Introduction Excited States Z – E Isomerizations [2 + 2] Photodimerizations [2 + 2] Photocycloadditions of Alkenes to Enones DI ‐π‐Methane Rearrangement

Renewable Cyclobutane-1,3-dicarboxylic Acid (CBDA) Building Block Synthesized from Furfural via Photocyclization

“…Just as with furfural, malonic acid is a bioadvantaged chemical, meaning petrochemical processes cannot compete with biochemical production. − The subsequent decarboxylation of the Knoevenagel adduct in the same pot gave 2-furanacrylic acid ( 2 ) in 87% isolated yield. , Our previous study showed that 2 can be dimerized directly through photocycloaddition in the solid state to give CBDA-2 (head-to-head dimer), and all other related reports have also suggested that the β-form crystal (head-to-head packing) is the preferred packing conformation of 2 . ,, As such, despite its great potential applications in materials, the cyclobutane-1,3-diacid (head-to-tail dimer of 2 , CBDA-5, shown in Scheme ) has never been reported before, as it would need to arise from the α-form crystal (head-to-tail packing) of 2 . It seems that the intermolecular hydrogen bonds in the solid state disrupt the weak complementary π–π stacking between adjacent acid molecules that could lead to the formation of the α-form crystal., − Thus, we hypothesized that ethyl 2-furancarylate might offer the desired α-form packing in the solid state because the strong intermolecular hydrogen bonds between the carboxylic acid groups are removed. ,,, …”