Synthesis of a Novel Cyclic Germanium Enamine from Germylene and 2-Vinylpyridine and Its Stereoselective Aldol Type Reaction with Aldehydes

A novel cyclic germanium(IV) enamine 3 has been prepared by the reaction of a germylene, bis[bis(trimethylsilyl)aminato]germanium(II) (1), and 2-vinylpyridine (2). The aldol type reaction of the resulting enamine with various aldehydes 4 gave condensation products of 4,5-disubstituted l-oxa-2-germacyclopentane derivatives 5. The reaction proceeds in a stereoselective manner to give trans products when aliphatic aldehydes were used as electrophiles. In the case of using aromatic aldehydes, cis isomers predominate. The preferential formation of a cis or trans isomer was explained by assuming an acyclic transition state for the aldol type reaction.