Chun-An Fan

Semipinacol Rearrangement in Natural Product Synthesis

[Song, Zhen-Lei] Sichuan Univ, Key Lab Drug Targeting, Educ Minist, Dept Med Chem,W China Sch Pharm, Chengdu 610041, Peoples R China

Organocatalytic Asymmetric Vinylogous α-Ketol Rearrangement: Enantioselective Construction of Chiral All-Carbon Quaternary Stereocenters in Spirocyclic Diketones via Semipinacol-Type 1,2-Carbon Migration

The catalytic enantioselective synthesis of all-carbon quaternary stereogenic centers in spirocyclic diketones has been achieved for the first time by an unprecedented asymmetric vinylogous alpha-ketol rearrangement in which an enantiocontrolled semipinacol-type 1,2-carbon migration was realized using multifunctional cinchona-modified primary amine catalysis.

Iron(III)‐Catalyzed and Air‐Mediated Tandem Reaction of Aldehydes, Alkynes and Amines: An Efficient Approach to Substituted Quinolines

Economic and practical advantages are offered by the iron(III)-catalyzed and air-mediated tandem coupling/hydroarylation/dehydrogenation of simple readily available aldehydes, alkynes, and amines for the synthesis of 2, 4-disubstituted quinolines (see scheme).

Au(I)-catalyzed rearrangement reaction of propargylic aziridine: synthesis of trisubstituted and cycloalkene-fused pyrroles.

A rearrangement reaction of propargylic aziridine, catalyzed by PPh(3)AuCl/AgOTf, forming trisubstituted and cycloalkene-fused pyrroles is described which involves an unusual tandem cyclization/ring-opening/Wagner-Meerwein process. The unique structures of the products demonstrated its potential applications for synthesizing structurally diverse alkaloids.

Spirocyclopropanation Reaction of para-Quinone Methides with Sulfonium Salts: The Synthesis of Spirocyclopropanyl para-Dienones

A novel DBU-mediated stereoselective spirocyclopropanation of para-quinone methides with sulfonium salts has been developed on the basis of the mode involving a 1,6-conjugate addition/intramolecular dearomatizing cyclization cascade. This reaction provides a mild and effective method for the assembly of synthetically and structurally interesting spirocyclopropanyl para-dienones. The feasibility for the enantioselective access to such functionalized para-dienones has also been explored by using the axially chiral sulfonium salt. Importantly, the regioselective ring openings of the related spirocyclopropanyl para-dienones have been achieved divergently.

An Efficient Total Synthesis of (±)-Stemonamine

An efficient first approach to the Stemona alkaloid (+/-)-Stemonamine has been developed on the basis of a key TiCl4 promoted tandem Semipinacol rearrangement/Schmidt reaction and a Dieckmann condensation reaction.

Asymmetric Total Synthesis of Apocynaceae Hydrocarbazole Alkaloids (+)-Deethylibophyllidine and (+)-Limaspermidine

An unprecedented asymmetric catalytic tandem aminolysis/aza-Michael addition reaction of spirocyclic para-dienoneimides has been designed and developed through organocatalytic enantioselective desymmetrization. A unified strategy based on this key tandem methodology has been divergently explored for the asymmetric total synthesis of two natural Apocynaceae alkaloids, (+)-deethylibophyllidine and (+)-limaspermidine. The present studies not only enrich the tandem reaction design concerning the asymmetric catalytic assembly of a chiral all-carbon quaternary stereocenter contained in the densely functionalized hydrocarbazole synthons but also manifest the potential for the application of the asymmetric catalysis based on the para-dienone chemistry in asymmetric synthesis of natural products.

Asymmetric synthesis of bioactive hydrodibenzofuran alkaloids: (-)-lycoramine, (-)-galanthamine, and (+)-lunarine.

Divergent route: a direct C-C bond-forming approach to the key aryl-substituted all-carbon quaternary stereogenic center present in bioactive hydrodibenzofuran alkaloids has been discovered. This approach involves an unprecedented organocatalytic enantioselective Michael addition of α-cyanoketones with acrylates and was used in a novel and divergent synthetic strategy for the title compounds in asymmetric fashion.

Diastereoselective and Enantioselective Synthesis of Unsymmetric β,β-Diaryl-α-Amino Acid Esters via Organocatalytic 1,6-Conjugate Addition of para-Quinone Methides

A novel strategy based on phase transfer catalysis for the diastereoselective and enantioselective direct assembly of unsymmetric β,β-diaryl-α-amino acid esters via 1,6-conjugate addition of para-quinone methides and glycine derivatives is described. This protocol also provides an alternative route to the synthetically interesting functionalized chiral tetrahydroisoquinoline and its analogues.

Formal syntheses of (+/-)-stemonamine and (+/-)-cephalotaxine.

A short and efficient approach to aza-quaternary pyrrolo[1,2-a]azepine 8 and aza-quaternary indolizine 23, as the crucial intermediates for syntheses of stemonamine (1a) and cephalotaxine (1b), has been developed on the basis of the key intramolecular Schmidt reaction of symmetric azido-diones 5 and 18, respectively.