Stereoselective Tandem Synthesis of Pyrrolidine Derivatives under Gold Catalysis: An Asymmetric Synthesis of (-)-Lepadiformine A

Gold-catalyzed cyclization and cycloaddition in natural product synthesis

Covering: 2016 to mid 2023Transition metal catalysis, known for its remarkable capacity to expedite the assembly of molecular complexity from readily available starting materials in a single operation, occupies a central position in contemporary chemical synthesis. Within this landscape, gold-catalyzed reactions present a novel and versatile paradigm, offering robust frameworks for accessing diverse structural motifs. In this review, we highlighted a curated selection of publications in the past 8 years, focusing on the deployment of homogeneous gold catalysis in the ring-forming step for the total synthesis of natural products. These investigations are categorized based on the specific ring formations they engender, accentuating the prevailing gold-catalyzed methodologies applied to surmount intricate challenges in natural products synthesis.

Towards a General Access to 1-Azaspirocyclic Systems via Photoinduced, Reductive Decarboxylative Radical Cyclizations

A convenient and versatile approach to important 1-azaspirocyclic systems relevant to medicinal chemistry and natural products is reported herein. The main strategy relies on a reductive decarboxylative cyclization of redox-active esters which can be rapidly assembled from abundant cyclic azaacids and tailored acceptor sidechains, with a focus on alkyne acceptors enabling the generation of useful exo-alkene moieties. Diastereoconvergent variants were studied and could be achieved either through remote stereocontrol or conformational restriction in bicyclic carbamate substrates. Two sets of metal-free photocatalytic conditions employing inexpensive eosin Y were disclosed and studied experimentally to highlight key mechanistic divergences.

Au-catalyzed stereodivergent synthesis of 2,5-disubstituted pyrrolidines: total synthesis of (+)-monomorine I and (+)-indolizidine 195B

Stereodivergent synthesis of 2,5-disubstituted pyrrolidines was achieved via a Au-catalyzed tandem intramolecular alkyne hydroamination/iminium formation/Et3SiH reduction. Importantly, the stereochemical outcome could be switched by choosing an appropriate nitrogen protecting group. Total synthesis of a diastereomeric pair of alkaloid natural products, monomorine I and indolizidine 195B, was achieved to showcase the synthetic utility of the tandem reaction.

Total Synthesis of Pyrrolidine and Piperidine Natural Products via TMSOTf-Mediated "5/6-endo-dig" Reductive Hydroamination of Enynyl Amines

Stereoselective syntheses of pyrrolidines and piperidines bearing hydrophobic chains have been achieved through a metal free, Lewis acid-mediated 5/6-endo-dig reductive hydroamination cascade of enynyl amines. The brevity of the developed strategy allowed for the collective stereoselective total synthesis of various alkaloids, including (±)-pyrrolidine cis-225H, (±)-epi-197B, (±)-epi-225C, the family of (+)-solenopsins and (+)-isosolenopsins, and the formal synthesis of (±)-bgugaine and (+)-azimic acid.

Collective Asymmetric Total Synthesis of Cylindricines

Collective asymmetric total synthesis of marine tricyclic alkaloids, cylindricines A-H, and the proposed structures of cylindricines I and J was achieved in a concise manner from a single common spirocyclic pyrrolidine intermediate. A tandem chemoselective oxidation/intramolecular aza-Michael addition/epimerization was exploited to complete the tricyclic skeleton. This work provides a versatile synthetic entry to the cylindricine family of marine tricyclic alkaloids.

t-BuOK-Catalyzed Regio- and Stereoselective Intramolecular Hydroamination Reaction Leading to Phthalazinoquinazolinone Derivatives

We report herein an efficient and practical strategy for the preparation of 5H-phthalazino[1,2-b]quinazolin-8(6H)-one derivatives through a t-BuOK-catalyzed intramolecular hydroamination reaction of functionalized quinazolinones under extremely mild reaction conditions. A variety of quinazolinone substrates are well tolerated to furnish the corresponding products in good to high yields via an exclusive 6-exo-dig cyclization process. The present protocol has the advantages of readily obtainable starting materials, broad substrate scope, and high regio- and stereoselectivity.