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 sigma-bonds. When the reagent Ph3GeSnBu3 was employed in the Pd-0-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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheirn, Germany, 2004).