Enantioselective total syntheses of acylfulvene, irofulven, and the agelastatins

Abstract

I. Enantioselective Total Synthesis of (-)-Acylfulvene, and (-)-Irofulven We report the enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven, which features metathesis reactions for the rapid assembly of the molecular framework of these anti tumor agents. We discuss (1) the application of an Evans Cu-catalyzed aldol addition reaction using a strained cyclopropyl ketene thioacetal, (2) an efficient enyne ring-closing metathesis cascade reaction in a challenging setting, (3) the reagent, IPNBSH, for a late stage reductive allylic transposition reaction, and (4) the final ring-closing metathesis/dehydrogenation sequence for the formation of (-)-acylfulvene and (-)-irofulven. II. Total Synthesis of the (-)-Agelastatin Alkaloids The pyrrole-imidazole super-family of marine alkaloids, derived from linear clathrodinlike precursors, constitutes a diverse array of structurally complex natural products. The bioactive agelastatins are members of this family that have a tetracyclic molecular framework incorporating C4-C8 and C7-N12 bond connectivities. We provide a hypothesis for the formation of the unique agelastatin architecture that maximally exploits the intrinsic chemistry of plausible biosynthetic precursors. We report the concise enantioselective total syntheses of the agelastatin alkaloids, including the first total syntheses of agelastatins C and E. Our gram-scale chemical synthesis of agelastatin A was inspired by our hypothesis for the biogenesis of the cyclopentane C-ring and required the development of new transformations including an imidazolone-forming annulation reaction and a carbohydroxylative trapping of imidazolones.