Template-directed photochemical cycloaddition reactions of dienoic acids and studies toward fluoranthene synthesis

Abstract

Carbocyclic compounds are an essential class of organic compounds as they occur broadly in natural products and constitute the heart of pharmaceutically relevant compounds. Photochemical dimerization reactions exhibit great potential for the rapid synthesis of carbocyclic compounds. To circumvent the regio- and diastereoselectivity challenges associated with the photochemical dimerization reactions, template-directed solid-state (topochemical) reactions furnish an efficient solution. We utilized inexpensive and commercially available 1,8-dihydroxynaphthalene (1,8-DHN) as a covalent-bonding template for photochemical dimerization reactions of dienes. 1,8-DHN align the alkenes, fulfilling Schmidt’s criteria for topochemical reactions, and irradiation of template-bound diene gave products displaying high regio- and diastereoselectivity. Reaction conditions were optimized, which taught us that the powder, ground powder and ground crystals gave almost similar results. Furthermore, irradiation of template-bound diene in the solution resulted in a high yield and good diastereoselectivity. It should be noted that our work represents the first example of selective homodimerization and heterodimerization reactions of 5-arylpentadienoic acids. After irradiation, facile removal of the template was achieved by hydrolysis and transesterification reactions. Experiments to convert the divinylcyclobutane product to cyclooctadiene were not successful due to troubles with the Cope rearrangement reaction. In the second part, we aimed to synthesize the substituted fluoranthenes starting from 1,8-diiodonaphthalene. Functionalization of 1,8-diiodonaphthalene with Suzuki-Miyaura borylation to connect pyridazine ring as a dienophile for inverse electron-demand Diels-Alder reaction was tried under different conditions. Unfortunately, the reaction did not yield the desired conversion. To examine the possibility of the Ullmann coupling reaction, we performed studies with 1,8-diiodonaphthalene and iodobenzene under Ullmann coupling conditions, which resulted in complex mixtures.