Our specific aim is to develop synthetic organic transformations based on divalent germanium chemistry by: 1. The synthesis of beta-ketoesters and beta-diketones from aldehydes or olefins and diazoketones catalysed by MCl2 (M=Ge, Sn). 2. The preparation of a new class of compounds, germanium (II) epoxides. These compounds would serve as precursors for insertion reactions with unsaturated organic substrates, yielding diols and amino alcohols. 3. Generating germacyclopropanes and germahydroperoxides by the addition of GeX2 (X=Cl, OR NR2,...) to olefinic substrates or oxygen, followed by a trapping reaction. 4. The generation of 1,3-dipoles, by the addition of germanium (II) to unsaturated substrates which contain heteroatoms (e.g. aldehyde, nitrile), followed by intramolecular cycloaddition reactions. 5. The addition of germanium (II) to acetals to form ylide type intermediates which may undergo nucleophilic addition reactions followed by a selective intramolecular ligand transfer. 6. The utilization of divalent germanium for intramolecular insertion reactions to perform stereocontrolled rearrangements. The group IV elements, especially silicon and tin have received considerable attention in organic synthesis. Applications of germanium in organic chemistry however, remain exceedingly sparse. This seems somewhat unusual since germanium is sandwiched between silicon and tin, which are versatile synthetic tools. The methods which have been developed with group IV elements are extensive, but predominantly revolve around the highest oxidation states. One of the fundamental advantages of starting with a low valent species is that it will be able to perform several types of chemistry on an organic substrate as a function of its oxidation state, or change in oxidation state. In most cases the low valent species will be incorporated into a molecule while being oxidized to its higher oxidation state. As is will documented in the literature the high oxidation state of group IV elements already have a tremendous applicability in organic synthesis. Thus by starting with low valent germanium we can amplify its synthetic organic applicability by invoking selective chemistry associated with each oxidation state (the low valent aspects which are described in this proposal and the higher valent aspects derived from the literature). Germanium particularly lends itself particularly well to this task because it is the first divalent element in group IV (going down the column) which can be put in a bottle. Furthermore, a great number of these compounds are easily obtained in one or two steps from readily available starting materials. What remains is to determine the applicability of generating and trapping reactive germanium intermediates in a stereoselective manner.
| Specht, K M; Nam, J; Ho, D M et al. (2001) Determining absolute configuration in flexible molecules: a case study. J Am Chem Soc 123:8961-6 |
