Xialenons, New Pentalenons fromStreptomyces

Diastereoselective Synthesis of Bicyclo[3.3.0]octenones by Copper-Catalyzed Transannular Ring-Closing Reaction

A novel and efficient copper-catalyzed transannular ring-closing reaction of eight-membered rings has been developed that provides a straightforward way to synthesize bicyclo[3.3.0]octane derivatives in good yields. Mechanistic studies revealed that the reaction pathway might involve chlorination followed by the Kornblum reaction. Readily accessible starting materials and good functional group tolerance make this procedure attractive.

Rh(I)-catalyzed cyclocarbonylation of allenol esters to prepare acetoxy 4-alkylidenecyclopent-3-en-2-ones

A Rh(I)-catalyzed cyclocarbonylation reaction of allenol esters has been examined and its synthetic viability established for the conversion of trisubstituted allenes to bicyclo[4.3.0] and -[5.3.0] skeletons possessing an alpha-acetoxy cyclopentadienone. Tetrasubstituted allenol acetates gave elimination products, providing examples of a cyclocarbonylation reaction between an alkyne and a latent cumulene or cumulene equivalent. Cleavage of the acetate affords a free hydroxyl group illustrating the utility of this method for accessing alpha-hydroxy carbonyls from allenol esters.

Enantioselective total synthesis of (-)-xialenon A

The first total synthesis of (-)-xialenon A (1) via conjugate allylation of a 1,5-cyclooctadiene-derived bicyclo[3.3.0]octenone 3 and an alpha'-hydroxylation on the more hinderd face of enone 9 using hypervalent iodine chemistry, is described.