Toward the total synthesis of ritterazine N

Abstract

Zr-mediated equilibrating cyclocarbonylation of a designed triene led with high diastereocontrol to the ABC 6-6-5 tricyclic core of ritterazine N. The 5-5 EF spiroketal side chain of ritterazine N was prepared by equilibrating cyclization of an acyclic keto diol. The two components were coupled, and the D ring was assembled by intramolecular aldol condensation.

Total syntheses of natural products containing spirocarbocycles

“…There have been several published syntheses of the other 15 ritterazines and derivatives, but at the time of writing there has not yet been a published total synthesis of the spirocarbocycle-containing ritterazines. Taber et al have come the closest to synthesising ritterazine N (1.20, Scheme 2) and related analogues 18,19 by assembling a ritterazine N precursor. The final planned aldol cyclocondensation failed, but an alternative route via ozonolysis of an alkene followed by treatment with base successfully gave the related compound bis-18,18′-desmethylritterazine N (1.23).…”

“…The final planned aldol cyclocondensation failed, but an alternative route via ozonolysis of an alkene followed by treatment with base successfully gave the related compound bis-18,18′-desmethylritterazine N (1.23). 19,20 As this review aims to summarise the progress in the field, but also to identify areas for improvement, where natural pro-ducts have been synthesised by more than one strategy, the methods will be compared.…”