Synthetic Photochemistry. XXXIV. Synthetic Strategy of 5-8-5-Membered Tricyclic Higher Terpenoids Based on the Condensation of Two Optically-Active Iridoids, C10-Synthons Obtained from Photo-Cycloadduct of Methyl 2,4-Dioxopentanoate–Isoprene, and Its Application to a Synthesis of the Basic Carbon Skeleton of Fusicoccane

Abstract One of the photocycloadducts obtained during methyl 2,4-dioxopentanoate to isoprene was converted to optically active iridoids. Using a CrCl2 reductive-coupling reaction, proper combinations of two kinds of enantiomeric iridoids, 1-iriden-7-al and 9-benzyloxy-7-chloro-1-iridene, produced versatile intermediates for various types of 5-8-5-membered tricyclic natural products. From one such product, fusicocca-2,8,10(14)-triene (1) was synthesized by sequential transformations.