A Stereoselective Carbocyclization of Bis(allenes) with Germylstannane Catalyzed by Palladium Complexes

Diastereoselective germastannylation of bis(allenes) with germylstannanes, catalyzed by palladium complexes, for the construction of cis or trans five‐membered cyclic systems has been investigated. We observed that the relative stereochemical arrangements of the reaction products depends on the substituents in the reagents containing Ge−Sn σ‐bonds. When the reagent Ph3GeSnBu3 was employed in the Pd0‐catalyzed carbocyclization of bis(allenes), trans‐cyclized products and/or cis‐fused bicyclic dienes were produced. In contrast, cis cyclic compounds were obtained, again along with cis‐fused bicyclic dienes, from the reaction with Bu3GeSnBu3. NMR experiments to establish the stereochemical relationships and a mechanistic speculation for this transformation as a possible explanation for the different stereochemical outcomes are also described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)