Addition of Aldehydes to Germenes: The Influence of Solvent

The addition of trans-(2-phenylcyclopropyl)carboxaldehyde to dimesitylfluorenylidenegermane produced four diastereomers of a 1,2-oxagermin, 7a-d, 2,2,4,4-tetramesityl-1,3-dioxadigermetane (8), and fluorenylidene-(trans-2-phenylcyclopropyl)methane (9). The ratio of the products showed a strong dependence on the solvent: 7a-d were formed almost exclusively when ether or benzene was used as the solvent for the reaction, whereas 1,3-dioxadigermetane 8 and alkene 9 were the major products formed in THF. A mechanism is proposed to account for the observations.