Radical Cyclization of Alkene-Tethered Ketones Initiated by Hydrogen-Atom Transfer

Four-Step Synthesis of (-)-4-epi-Presilphiperfolan-8α-ol by Intramolecular Iron Hydride Atom Transfer-Mediated Ketone-Alkene Coupling and Studies to Access trans-Hydrindanols with a Botryane Scaffold

From an (R)-(+)-pulegone-derived building block that incorporates the stereo-defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four-step synthesis of (-)-4-epi-presilphiperfolan-8-α-ol was achieved. The key processes involved are a ring-closing metathesis leading to a bridged alkene-tethered ketone and its subsequent Fe^III -mediated metal-hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon-centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans-fused hydrindanols structurally related to botrydial compounds.

Electrochemical synthesis of 2-alkyl-4-phenylalkan-2-ols via cathodic reductive coupling of alkynes with unactivated aliphatic ketones

Herein, we present an efficient electrochemical method for synthesizing 2-alkyl-4-phenylalkan-2-ols through an electrochemically driven cathodic reductive coupling of the terminal and internal acetylenes with unactivated aliphatic ketones under mild conditions. The process proceeds through a ketyl radical, which then activates the aryl acetylene and causes complete reduction of the triple bond of the acetylene moiety. This strategy is environmentally benign and exhibits a broad substrate scope with ubiquitously available starting materials.

Hydrogen Atom Transfer-Mediated Cyclisations of Nitriles

Hydrogen atom transfer-mediated intramolecular C-C coupling reactions between alkenes and nitriles, using PhSiH₃ and catalytic Fe(acac)₃ , are described. This introduces a new strategic bond disconnection for ring-closing reactions, forming ketones via imine intermediates. Of note is the scope of the reaction, including formation of sterically hindered ketones, spirocycles and fused cyclic systems.

A Unified Approach for the Assembly of Atisine- and Hetidine-type Diterpenoid Alkaloids: Total Syntheses of Azitine and the Proposed Structure of Navirine C

A tetracyclic dinitrile was synthesized in twelve steps from cyclohex-2-en-1-one by using a chelation-triggered conjugate addition to a γ-hydroxy-substituted α,β-unsaturated nitrile and an oxidative dearomatization/Diels-Alder cycloaddition cascade as the key steps. The first total synthesis of azitine (in 17 steps) was achieved through a simple reductive cyclization of this intermediate and subsequent transformations while the total synthesis of the proposed structure of navirine C (in 19 steps) was accomplished by a hydrogen-atom-transfer reaction of the tetracyclic dinitrile, Pd/C-catalyzed reductive cyclization, and subsequent functional group manipulation.