Synthese von (+)-Phyllanthocin über eine metallkatalysierte Cycloreduktion

Copper Catalyzed [3+2] Annulation Reaction of Exocyclic Sulfonyl Enamides for the Synthesis of N,O-Spiroketal and Spiroketal

A copper-catalyzed [3+2] annulation reaction of exocyclic enamines/enol ethers with 1,4-benzoquinone esters has been developed, providing facile access to N,O-spiroketals and spiroketals under mild conditions with broad substrate scope (26 examples, 71-94 % yields). Gram scale synthesis and chemical transformations demonstrated that this method is potentially useful in the synthesis of natural products and drugs containing a N,O- spiroketal moiety. The chiral N,O-spiroketal could be obtained with 98 % ee after recrystallization, when a chiral SaBOX ligand was employed.

Facile Stereoselective Approach to Diverse Spiroheterocyclic Tetrahydropyrans: Concise Synthesis of (+)-Broussonetine G and H

A highly diastereoselective copper-catalyzed multicomponent cyclization of exocyclic enol ethers/enamines with methylene malonate and aldehydes has been developed to furnish spiroheterocyclic tetrahydropyrans in high yields with greater than 95:5 d.r. This method is practical, in that 36 examples, including a range of aldehydes and exo-vinyl heterocycles, are presented. By applying the newly developed method, the total synthesis of (+)-broussonetine G and formal synthesis of (+)-broussonetine H were achieved in a concise way.

Synthesis of spirocyclic C-arylglycosides and -ribosides by ruthenium-catalyzed cycloaddition

Spirocyclic C-arylglycosides were synthesized from the appropriately protected delta-gluconolactones. Addition of lithium acetylide followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the delta-gluconolactones into silylated diynes. After desilylation, subsequent ruthenium-catalyzed cycloaddition of the resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylglycosides in good yields and selectivity. This strategy was also extended to the synthesis of spirocyclic C-arylribosides from the known gamma-ribonolactone derivative. Moreover, silver-catalyzed iodination of the sugar diynes followed by ruthenium-catalyzed cycloaddition with acetylene delivered spirocyclic C-iodophenylglycosides and -ribosides, which were subjected to palladium-catalyzed C-C bond-forming reactions and copper-catalyzed coupling with nitrogen heterocycles to lead to various derivatives.