Total syntheses of several iridolactones and the putative structure of noriridoid scholarein A: an intramolecular Pauson–Khand reaction based one-stop synthetic solution

Abstract

A general synthetic strategy featuring a diastereoselective intramolecular Pauson–Khand reaction (IPKR) and some tactical synthetic manoeuvres to access ten iridoids in a stereocontrolled manner is delineated.

Four New Iridoid Metabolites Have Been Isolated from the Stems of Neonauclea reticulata (Havil.) Merr. with Anti-Inflammatory Activities on LPS-Induced RAW264.7 Cells

“…Twenty compounds were isolated from the EtOAc fraction by silica gel column chromatography and normal-phase, semi-preparative, high-performance liquid chromatography (HPLC). Among these compounds, we isolated one new iridoid, which namely neonanin C ( 1 ) (neonanin A and B have been reported in our previous study [9]), one monocyclic iridoid ring-opened derivative namely neonanin D ( 2 ), two new bis-iridoid derivatives namely reticunin A ( 3 ), reticunin B ( 4 ) and sixteen known compounds, including strychnovoline ( 5 ) [15], siphonostegiol ( 6 ) [16], isoboonein ( 7 ) [17], floribundane B ( 8 ) [18], alyxialactone ( 9 ) [19], syringaresinol ( 10 ) [20], (+)-pinoresinol ( 11 ), (+)-medioresinol ( 12 ) [21], 4-methoxycatechol ( 13 ) [22], protocatechuic acid ( 14 ) [23], trans -caffeic acid ( 15 ) [24], syringic acid ( 16 ) [25], 3-hydroxy-1-(4-hydroxy 3,5-dimethoxyphenyl)-1-propanone ( 17 ) [26], ferulic acid ( 18 ) [27], protocatechuic acid methyl ester ( 19 ) [28], C-veratroylglycol ( 20 ) [29]. The structures of the new compounds were determined through spectral analyses, including IR, UV, 1D- and two-dimensional (2D)-NMR, as well as HR-ESI-MS data.…”

Application of Pauson–Khand reaction in the total synthesis of terpenes

“…91 In spite of the appearance of these reports among the others, a literature survey disclosed few reports on the total synthesis of diverse oxy-functionality pattern observed on the cyclopentane ring of the iridoid framework. 89,92,93 In 2019, Khan and co-workers reported an efficient and economic strategy to have access to several iridoids (65, 68, 68 0 , 70, 71, 72, 75, 75 0 , 79) 94 using an intramolecular Pauson-Khand reaction (IPKR) as the crucial step to access ten iridoids in a stereoselective fashion. In their strategy, bicyclic ether 61 was found to be an important intermediate, since it contains the iridoid scaffold as well as bearing a carbonyl functionality at the C6 position and tosylate at the C4 position.…”

Recent Advances in Iridoid Chemistry: Biosynthesis and Chemical Synthesis

“…Khan and coworkers aimed to synthesize iridolactones with a strategy based on using an intramolecular Pauson‐Khand reaction (IPKR) (Scheme 11). [45] For effective synthesis of this series of iridoids, the common intermediate 112 is prepared. First, the key Pauson‐Khand reaction is investigated using silyl protected enyne ether 110 that is derived from solketal.…”