Dearomative (3 + 2) Cycloaddition of Indoles for the Stereoselective Assembly of Fully Functionalized Cyclopentanoids

The gold(I)-catalyzed dearomative cyclopentannulation of various indoles with 2-ethynyl-1,3-dithiolane is reported. The method generates three new stereocenters with excellent control of relative stereochemistry and is tolerant of diverse functionalization and substitution patterns on the indoles. The obtained cyclopentane-fused indolines allow for interesting subsequent synthetic manipulations, giving rise to fully substituted cyclopentanes with control of the relative stereochemistry of all five stereocenters. The reported reaction illustrates and elucidates a mechanistic dichotomy underlying gold(I)-catalyzed reactions of 2-ethynyl-1,3-dithiolane.

Stereoselective Gold(I)-Catalyzed Vinylcyclopropanation via Generation of a Sulfur-Substituted Vinyl Carbene Equivalent

A stereoselective gold(I)-catalyzed vinylcyclopropanation of alkenes has been developed. A gold-coordinated cationic vinyl carbene species, readily generated via a rearrangement of the ethylenedithioacetal of propargyl aldehyde, reacts with a wide range of alkenes to afford thio-substituted vinylcyclopropanes. The gold-catalyzed vinyl cyclopropanation proceeds under mild conditions at room temperature and is generally selective for the formation of cis-substituted cyclopropanes. The reaction allows the formal introduction of a "naked" vinyl carbene, by subsequent chemoselective hydrodesulfurisation of the ethylenedithio-bridge. The synthetic utility of the new method is demonstrated by a short, racemic formal synthesis of the alkaloid cephalotaxin, hinging on a key vinyl cyclopropane-cyclopentene rearrangement.

An Intramolecular Cycloaddition Approach to the Kauranoid Family of Diterpene Metabolites

Synthetic studies toward the ent-kauranoid family of diterpene natural products are reported. An intramolecular (4 + 3) cycloaddition allows the direct elaboration of diverse natural product frameworks, encompassing a challenging bicyclo[3.2.1]octane core. The established routes comprise only a few synthetic operations (3-5 steps), transforming a range of simple starting materials into the tetracyclic scaffolds that are commonly found in many ent-kaurene metabolites.