Biomimetic synthesis of pallavicinin, neopallavicinin, pallambins A–D, pallaviambins A/B, and pallavicinolides B/C

Abstract

Inspired by the proposed biogenic skeletal diversification process, the divergent total syntheses of 10 structurally complex pallavicinia diterpenoids with three distinct carbon skeletons, pallavicinin, neopallavicinin, pallambins A–D, pallaviambins A/B, and pallavicinolides B/C, were accomplished. Among them, the total syntheses of pallaviambins A/B and pallavicinolides B/C were achieved for the first time, and the synthetic routes of pallavicinin, neopallavicinin, and pallambins A/B were the shortest. The total syntheses feature a stereoselective Ireland-Claisen rearrangement to construct the C10 quaternary carbon stereocenter, the 2-fluoroethyl vinyl ether used as a masked methyl ketone for the first time, a biomimetic C2–C8 aldol reaction to construct the pallavicinin skeleton, a biomimetic cascade reaction of C4–C8 aldol reaction/oxa-Michael addition/MeOH elimination for the synthesis of pallambins C/D, and the spontaneously intramolecular Diels-Alder reaction to generate the pallavicinolide skeleton.