| Research Abstract |
Euglobal and robustadials were isolated from Encalyptus spp. as inhibitors of the Epstein-Barr virus activation, or as antimalarial compounds. Previously we reported an electrochemical generation of o-quinomethane and their cycloaddition with α-phellandrene to yield the euglobal Ia_1 and Ia_2 skeletons. Furthermore, the first, concise synthesis of natural euglobals has been accomplished by biomimetic cycloaddition of monotermpenes and quinomethanes generated in situ by oxidation of grandinol. In this paper, we introduced novel thermomorphic reaction systems that enable high-throughput synthesis of eublobal and robustadial skeletons via intermolecular hetero Diels-Alder reaction of terpenes and anodically generatefd o-quinomethanes.the thermomorphic liquid-liquid separation system composed of organic solvents of different polarity might allow for extremely efficient reactions, for example, by the association of apolar products and polar substrates or catalysts in a one-phase solution, w
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hich could be spatially separated after the completion of reactions. It should further open the door for the construction of liquid-phase combinatorial chemistry, industrial and green chemistry by the ease of the separation of products, catalyses, reagents, electrolytes, and/or soluble platforms for organic synthesis. This gave us the incentive to explore a novel thermomorphic reaction system using typical organis solvents. Among numerous compositions of organic solvents, an appropriate mixture of cyclohexane (CH) and nitroalkane (NA) was initially found to show the desired function, that is, a 75 : 25 (v/v) mixture of CH and NA [a 20 : 80 v/v mixture of nitromethane (NM) and nitroethane (NE)]. At 25℃, the solvent mixture was separated into an upper CH(main) phase and a lower NA(main) phase. temperature with an increase in the CH ratio to complete the one-phase formation. By using this system, several euglobal and robustadial skeletons could be synthesized just by changing alkenes (dienophiles for intermolecular hetero-Diels-Alder reaction), and most of the products were isolated from upper layer just by cooling to form the biphasic solution system after the completion of the reaction. Less
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