A-germylation

Addition of a silylgermane to phenylacetylene is catalyzed by Pd(PPh3)4 at 120 °C to give (Z)-a-germyl-/ -silylstyrene in 48% yield (Equation (105)).250... 

Transient digermene 86 was postulated as possible intermediate in the reaction of 1,2-dichlorodigermacyclobutane 87 with Mg/MgBr2 in the presence of an alkene, leading to the bicyclic compound 8878 [Eq. (17)]. However, an electron transfer reaction with the intermediate formation of a germyl radical is also a possibility.78 Similarly, transient 1,2-digermacyclobu-... 

Yates, K. Agolini, F. The importance of inductive effects in a-silyl and a-germyl ketones. Can.]. Chem. 1966, 44, 2229-2231. 

A. Reaction Mechanisms of the Photolyses of a-Germyl Ketones in Various Media... 

In the frame of the proposed mechanism, the primary act of the photolysis of a-germyl... 

Earlier suggestions of the involvement of free radical intermediates have stimulated the application of spin chemistry methods to the investigation of the detailed mechanism of the photolysis of a-germyl ketones in either polar or nonpolar solvents, in the presence or in the absence of traps of element-centered free radicals. Of special interest are problems of the multiplicity of the reactive state, and the transformations of the element-centered free radicals in the bulk. 

The question of the multiplicity of the reactive state in the photolysis of a-germyl ketones is rather controversial. An attempt to apply laser pulse photolysis techniques... 

The silyl and germyl groups are (x-donors and 7I -acceptors Calculated CC distances in silyl- and germyl cyclopropane suggest that the Ti-acceptor character is significantly more pronounced for a silyl than a germyl substituent. 

These reactions seldom offer advantages over hydride reductions, except if GeD bond formation in a complex molecule, such as a germyl-metal species, is involved ... 

Yamamoto reported that trapping of a hthium enolate, derived from 3-methyl-2-butenoate, wifh MesGeX selectively gave a-germylated derivative (2) (Scheme 11.5) [17]. Trapping with Mf. SifJ or BujSnGl afforded O-silylated product (3) or y-stan-nylated compound (4) respectively. 

The a-germylation is a reflection of kinetic control, whereas y-stannylation is thermodynamic controlled. The C-Ge bond is stronger than the C-Sn bond. D(Ge-Et) = 237 kJ mok, D(Sn-Et) = 193 kJ mok. a-Germyl ester (2) played the role of a Ge-masked dienolate equivalent. Thus, Lewis acid-mediated addition of the a-germyl ester (2) to an acetal (Scheme 11.6) [17, 18], diefhylazodicarboxylate... 

Addition of a germyl copper(I) reagent to acyl halides has afforded acylgermanes in excellent yield (Scheme 11.57) [83]. 

---