Cobalt versus Osmium: Control of Both trans and cis Selectivity in Construction of the EFG Rings of Pectenotoxin 4

Abstract

Catalytic oxidative cyclisation reactions have been employed for the synthesis of the E and F rings of the complex natural product target pectenotoxin 4. The choice of metal catalyst (cobalt- or osmium-based) allowed for the formation of THF rings with either trans or cis stereoselectivity. Fragment union using a modified Julia reaction then enabled the synthesis of an advanced synthetic intermediate containing the EF and G rings of the target.

Rhodium-catalysed vinyl 1,4-conjugate addition coupled with Sharpless asymmetric dihydroxylation in the synthesis of the CDE ring fragment of pectenotoxin-4

“…8) into the desired enone 35 , with the unsaturated ethyl ester side chain serving as a precursor for a Julia olefination coupling with the FG ring fragment. Therefore, the previously reported E fragment enantiopure 29 (ref. 8) was deprotected with TBAF, before Parikh–Doering oxidation to the aldehyde and vinyl Grignard reagent was added to afford allyl alcohol 30 (Scheme 7).…”

“…To further test this methodology in the synthesis of pectenotoxin-4, we converted the desired E ring fragment 29 (ref. 8) into the desired enone 35 , with the unsaturated ethyl ester side chain serving as a precursor for a Julia olefination coupling with the FG ring fragment.…”

“…We have successfully synthesised the C-1 to C-16 ABC fragment via a double osmium catalyzed oxidative cyclisation together with a hydride-shift-initiated spiroketalisation,7 as well as preparing the C-21 to C-40 EFG fragment via stereodivergent catalytic cobalt and osmium oxidative cyclisations (Scheme 1a). 8…”

The dioxasilepanyl group as a versatile organometallic unit: studies on stability, reactivity, and utility

“… 21 A similar structure is also found in another reported X-ray structure of a dioxasilepane ring. 22 Meanwhile, the 1 H NMR spectrum of 1-VII shows that the four ethylene protons of the dioxasilepane core appear as one broad signal. This is in contrast to the methylene protons in the dioxasilynane moiety of 1-VI that show two independent signals in the 1 H NMR spectrum.…”

Σύνθεση Φυσικών Τερπενίων Ή/Και Αναλόγων Τους Με Πιθανή Βιολογική Δράση

“…Ένα τελευταίο παράδειγμα χρήσης της αντίδρασης Julia-Kocienski στα φυσικά προϊόντα είναι από την ομάδα του T. J. Donohoe και των συνεργατών του στα τελευταία στάδια της σύνθεσης των EFG δακτυλίων του αντικαρκινικού μακροκυκλικού πολυαιθέρα pectenotoxin 4 (138, Σχήμα 17). 93…”