Synthetic Studies towards Pectenotoxin‐2: Synthesis of the Nonanomeric 10‐epi‐ABCDE Ring Segment by Kinetic Spiroketalization

Abstract

The synthesis of the nonanomeric 10‐epi‐ABCDE ring system of pectenotoxin‐2 has been achieved by using a kinetic spiroketalization reaction. The synthesis of the spiroketalization precursor was achieved through a cross‐metathesis/hydrogenation sequence. The formation of the epi‐C10 isomer resulted from an unexpected anti‐Felkin selective addition of organometallic nucleophiles to the advanced CDE ring precursor. This addition reaction was investigated with differently protected α,β‐dioxygenated model aldehydes, which displayed similar anti‐Felkin selectivities with organometallic nucleophiles.

Mukaiyama–Michael Reactions with Acrolein and Methacrolein: A Catalytic Enantioselective Synthesis of the C17–C28 Fragment of Pectenotoxins

“…PTX4 and PTX8 are the only members of the PTX family that have been produced synthetically . We have previously recorded efforts aimed at the synthesis of the most active congener, PTX2, which bears as an additional synthetic challenge a thermodynamically unstable “nonanomeric” spiroketal …”

Synthesis of Decytospolide A, B and Their C-3 Epimers Using Stereoselective­ Oxypalladation

“…The primary hydroxy group of 10 was oxidized with Dess-Martin periodinane followed by treatment with npentylmagnesium bromide in the presence of MgBr 2 to give 8 as a single diastereomer. 16 Determination of the absolute configuration of the newly formed chiral center was not performed at this stage. Cross-metathesis reaction of 8 with 5 equivalents of allyl 2-naphthoate (7) afforded cyclization precursor 6 in 90% yield (E/Z = 10:1).…”