Construction of 6,10-syn- and -anti-2,5-Dioxabicyclo[2.2.1]heptane Skeletons via Oxonium Ion Formation/Fragmentation: Prediction of Structure of (E)-Ocellenyne by NMR Calculation

Abstract

A highly efficient and stereoselective route to potential synthetic intermediates for ocellenyne and related C acetogenin natural products with 6,10-syn- and 6,10-anti-2,5-dioxabicyclo[2.2.1]heptane core structures has been developed by means of an iterative biogenesis-inspired oxonium ion formation/fragmentation sequence. In accordance with chemical transformations, the most likely stereostructure for (E)-ocellenyne on the basis of GIAO C NMR calculations possesses a 6,10-anti-2,5-dioxabicyclo[2.2.1]heptane core, as predicted from a plausible biosynthetic pathway, instead of the spectroscopically proposed 6,10-syn-2,5-dioxabicyclo[2.2.1]heptane skeleton.

Synthesis, Characterization, and Reactivity of Complex Tricyclic Oxonium Ions, Proposed Intermediates in Natural Product Biosynthesis

“…Alternatively, opening of 20 with bromide ion at C-13 would give the ocellenyes, 54 the full stereostructures of which have recently been tentatively reassigned based on DFT calculations and biogenetic considerations as 23. 55…”

“…Opening of the oxonium ions 20 at C-10 or C-7 with bromide or chloride ions would generate the natural products 19 , 21 , 22 , and 24 . Alternatively, opening of 20 with bromide ion at C-13 would give the ocellenyes, the full stereostructures of which have recently been tentatively reassigned based on density functional theory (DFT) calculations and biogenetic considerations as 23 . , …”

Forwards and backwards – synthesis of Laurencia natural products using a biomimetic and retrobiomimetic strategy incorporating structural reassignment of laurefurenynes C–F

“…35 Among the acetogenic Laurencia natural products whose structures have been reassigned are laurefucin, 36,37 obtusallenes V, VI and VII, 16,19,26 elatenyne, [12][13][14][15]38 laurendecumenyne B, 15,39,40 aplysiallene, 41,42 a chloroenyne from Laurencia majuscula 13,34,38,43 and laurefurenynes A and B, [20][21][22] additionally the structures of the ocellenynes have been tentatively reassigned on the basis of biogenetic considerations and DFT calculations of NMR chemical shis. 24,44,45 The laurefurenynes are a series of six acetogenic natural products which were isolated and characterized by Jaspars and co-workers from a sample of Laurencia sp. collected in the Philippines in 1991.…”

Structure Determination of a Chloroenyne from Laurencia majuscula Using Computational Methods and Total Synthesis

“…Flexible, halogenated natural products epitomize this challenge and have been variously misassigned. 9…”

“…Although elegant synthetic approaches have been developed to access multiple diastereomers of a target molecule, the ability to predict the most plausible relative and absolute configuration of flexible natural product structures is desirable. Flexible, halogenated natural products epitomize this challenge and have been variously misassigned …”