Total Synthesis of Arylnaphthalene Lignans through a Photochemical Key Step

The total syntheses of three arylnaphthalene lignans (ANLs) were developed: Vitrofolal E (1), Noralashinol C (2), and Ternifoliuslignan E (3). These natural products have in common a missing substituent in 2-position of the naphthalene moiety (2H-ANLs). The key step of these syntheses is a regioselective intramolecular Photo-Dehydro-Diels-Alder (PDDA) reaction with (1,7)naphthalenophanes as primary products. A further improvement of the photochemical step was achieved by triplet sensitization with xanthone, allowing the use of more efficient UVA lamps. It should be noted that this work is a continuation of a previous publication about the total synthesis of lignans using the PDDA reaction.([1])