Total Synthesis of Panaginsene

Abstract

The total synthesis of panaginsene has been accomplished in 11 linear steps starting from methyl 3,3dimethyl-5-oxocyclopent-1-ene-1-carboxylate. The key steps are a Sharpless asymmetric epoxidation and Ti(III)mediated reductive epoxide opening-radical cyclization to construct the chiral quaternary carbon stereocenter followed by a very challenging HWE olefination reaction on an 1,3-keto aldehyde and a late stage McMurry olefination using low valent titanium to construct the highly constrained angular tetrasubstituted olefin in a five-membered ring.

Stereoselective Synthesis of Acyclic Tetrasubstituted Alkenes from Anilines by Dearomatization and Trimethylenemethane Cycloaddition

“…Because of this, synthetic chemists have developed novel methodologies to produce all-carbon tetrasubstituted alkenes . Carbonyl olefination, elimination of appropriate alkanes, olefin metathesis of 1,1-disubstituted olefins, insertive coupling of internal alkynes via carbometalation and cross coupling reactions or addition to electrophiles, and C–H functionalization of olefins have all been examined. Notwithstanding the remarkable achievements that have been made, efficient stereoselective synthesis of all-carbon tetrasubstituted alkenes, especially acyclic alkenes, remains a daunting challenge, mainly caused by their congested structures.…”