Synthesis of Methyl 1-Hydroxy-6-oxo-2-cyclohexenecarboxylate, a Component of Salicortin and Tremulacin, and the Monomer of Idesolide

Silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with malonyl peroxides in solvent-free conditions

For the first time silica gel was observed to activate peroxides in oxidative coupling reactions. Here we report silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with cyclic diacyl peroxides affording α-acyloxy derivatives with 100% atom efficiency. The highest yields of coupling products were achieved in solvent free conditions. C–O coupling products were prepared in yields up to 86%.

Explorations of caffeic acid derivatives: total syntheses of rufescenolide, yunnaneic acids C and D, and studies toward yunnaneic acids A and B

Yunnaneic acids A-D, isolated from the roots of Salvia yunnanensis , are hexameric (A and B) and trimeric (C and D) assemblies of caffeic acid that feature an array of synthetically challenging and structurally interesting domains. In addition to being caffeic acid oligomers, yunnaneic acids A and B are formally dimeric and heterodimeric adducts of yunnaneic acids C and D. Herein we report the first total syntheses of yunnaneic acids C and D featuring the formation of their bicyclo[2.2.2]octene cores in a single step from simple precursors via an oxidative dearomatization/Diels-Alder cascade that may have biogenetic relevance. In addition, exploitation of the key intermediate resulting from this cascade reaction has enabled rapid access to the structurally related caffeic acid metabolite rufescenolide through an unexpected Lewis acid-mediated reduction. Finally, we report the results of extensive model studies toward forming the dimeric yunnaneic acids A and B. These explorations indicate that the innate reactivities of the monomeric fragments do not favor spontaneous formation of the desired dimeric linkages. Consequently, enzymatic involvement may be required for the biosynthesis of these more complex family members.

Explorations into neolignan biosynthesis: concise total syntheses of helicterin B, helisorin, and helisterculin A from a common intermediate

Helicterins A and B (1 and 2), helisorin (3), and helisterculin A (4) are structurally unique natural products with the ability to combat the avian myeloblastosis virus. Biogenetically, their architectures are considered to be products of seemingly straightforward Diels-Alder, radical-based, or acid-induced dimerizations of common, simpler precursors. Yet, the pursuit of such blueprints in the laboratory has failed thus far in enabling their successful synthesis. Herein, we describe the first total syntheses of three of these natural products. Key features include the use of a building block distinct from Nature's likely starting material, highly complex retro Diels-Alder/Diels-Alder reaction cascades, an unconventional protecting group to achieve the proper balance of chemical reactivity on sensitive scaffolds, and several carefully developed reaction conditions that effectively balance competing reaction pathways.