The treatment of α,β-unsaturated ketones with divalent germanium salts cleanly generated C, O-chelated germyl enolates. The aldol reactions of the chelated enolates with the aldehydes achieved a high diastereoselectivity in the construction of the five-membered aldol adducts. Furthermore, the subsequent transformation of the Ge-C bond in the aldol adduct enabled the stereocontrolled synthesis of triols bearing four asymmetric centers.

The Group 14 enolates play an important part in many organic reactions. Herein, the reduction of an α-bromo ketone with germanium(II) salts cleanly afforded the corresponding germyl enolate as an isolatable species. This experimental reductive generation of a germyl enolate enabled us to characterize both C- and O-bound tautomers derived from an identical precursor and to unveil the tautomeric mechanisms, including the kinetic parameters and the relative stability of these tautomers, along with confirmation from DFT calculations. Moreover, the highly coordinated germyl enolates were isolated by a stabilization process induced by adding ligands. All products were characterized by NMR spectroscopy and X-ray crystallography.

The molecular precursor Ge(OtBu)2 was combined with soluble hydride sources to either yield metastable [GeH2]n materials (orange solids) or the deposition of nanoscale films of Ge from solution.

Allylgermanes with a 4-, 5-, and 6-coordinated germanium center were characterized by X-ray crystallography. Cationic 6-coordinated group 14 allylmetals, which were hitherto assumed to be a transition-state structure of allylations, were successfully isolated. Forming high coordination states significantly enhanced the reactivity of the allylgermanes. In contrast to the 4-coordinated allylgermanes with low reactivity, the highly coordinated species readily reacted with several aldehydes. Furthermore, the high coordination states exerted a significant effect on the E/Z selectivity of allylation depending on external additives. The coordination structure had a dramatic influence on the electronic and steric environments around the Ge center, enabling the geometrically controlled allylation of aldehydes. Allylic organometallic reagents are indispensable nucleophiles for carbon-carbon bond-forming reactions. [1] Many types of allylmetals, which include different metal centers, such as Mg, [2] Zn, [3] B, [4] In, [5] Si, [6] or Sn, [5b,7] have been utilized for the allylations of carbonyls or imines. The metal center of the allylmetal is the paramount factor that determines the transition-state structure. Control of the transition-state structure, either acyclic-or cyclic, has attracted considerable attention because the difference in the structure deeply reflects stereoselective bond formations. The group 14 allylmetals, allylsilanes or stannanes, have served as interesting subjects for this study. They possibly assume both of the acyclic and cyclic transition states depending on the reaction conditions [8] and substituents on the metal [9] or additive ligands. [10] The coordination of the ligands into the metal center dictates the reactivity of the allylsilanes and governs the nucleophilicity of the allylic moiety and/or the Lewis acidity of the metal center.

The synthesis of α-alkenyl α,β-unsaturated ketones using germanium­(II) salts is reported. Oxagermacycles derived from α,β-unsaturated ketones with germanium­(II) salts and aldehydes can be transformed into α-alkenyl α,β-unsaturated ketones. Ammonium salts promoted the elimination of Ge­(II) species to afford the two classes of α-alkenyl α,β-unsaturated ketones in good yields. The α-alkenyl α,β-unsaturated ketones are precursors for multisubstituted heterocycles.