Total Synthesis of the Angucylinone Antibiotic (+)-Rubiginone B2

A new chiral synthesis of (+)-rubiginone B2 is reported. The intramolecular cobalt-mediated [2+2+2]-cycloaddition of a triyne precursor, synthesized from (+)-citronellal, afforded a chiral anthracene, which led after a two-step oxidation to the angucycli­none antibiotic

Synthesis of the Benz[a]anthraquinone Core of Angucyclinone Antibiotics

A general method for the synthesis of benz[a]anthraquinones is reported. The key step is a catalytic cobalt-mediated [2+2+2]-cycloaddition of a triyne, which affords an angularly substituted tetracycle. Oxidation of this core gives the typical structure of angucyclinone antibiotics

Synthesis of (3S)-Hydroxyandrosta-5,7-diene-17-ones via Intramolecular Cobalt-Mediated [2+2+2] Cycloaddition

A new method for the synthesis of lumisterin-type steroids following the D→ABCD approach is reported. A key step is the cobalt-induced cyclization of a cyclopentanoid enediyne, which was prepared via thioalkylation of the zinc enolate of a 2,3-substituted cyclopentanone with α-chlorosulfides

[2+2+2]-Cycloaddition of 4-Hydroxy-Substituted Enediynes to 2-Hydroxy-Substituted Decahydrophenanthrenes

Enediynes rac-4 were prepared in seven steps with an overall yield of 31% starting from 4-pentyn-1-ol (5). A cobalt mediated [2+2+2]-cycloaddition of these enediynes and subsequent removal of the metal fragment afforded the decahydrophenanthrenes rac-3/13 in 37-56% yield

Cobalt-mediated regioselective synthesis of substituted tetrahydroquinolines

A regioselective synthesis of polycyclic substituted ­pyridines is reported. Key step is the cobalt-catalyzed intramole­cular cyclization of diynenitriles, tethered by a silicon oxygen bond. Subsequent opening of the Si-O ring led then to the related tetra­hydroquinolines

3-Substituted and 2,3-Disubstituted Cyclopentanones via an Asymmetric Tandem 1,4-Addition/Dieckmann Cyclization

A new stereoselective method for the synthesis of 3-substituted and 2,3-disubstituted cyclopentanones is described. The key step is the 1,4-addition of a cuprate to a chilar Michael-acceptor derived from (-)-8-phenylmenthol or the Helmchen auxiliary followed by Dieckmann cyclization of the obtained chiral enolates. The resultant 2,3-cyclopentanones can be transformed after methanolysis and demethoxycarbonylation to the related 3-substituted ­cyclopentanones