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Thermolysis of hexamesitylcyclotrigermane in the presence of various derivatives of pbenzoquinone are described. A surprising 1,3-cycloadduct was isolated in the case of pbenzoquinone; it is the first example of a 1,3-cycloaddition of a digermene to a quinone followed by a 1,4-H shift. The X-ray crystal structure of the adduct reveals a planar configuration of fused fiveand six-membered rings and a deformation of the heterocycle because of the germanium atoms. Two other p-quinones substituted in ortho positions by aromatic cycles (naphthoquinone and anthraquinonej were used to decrease the fraction of the rearranged cycloadduct and thereby to increase the oligomeric forms. Introduction Recently we described the reactions of hexamesitylcyclotrigermane with various adiketones and showed that they proceed by a pathway involving radicals to give cyclic and polymeric compounds. The mechanism of the addition of carbonyl compounds such as aldehydes or ketones to disilene or germasilene (generated by photolysis of the corresponding trimetalla compounds) has been determined. These authors also proposed the formation of biradical intermediates which gave disproportionation or ring closure. On the other hand, it has been reported that the photolysis of cyclic organosilanes with phenantraquinone gave silylene insertion products by a process involving radicals. We now report reactions of cyclotrigermane with pbenzoquinone, p-naphthoquinone and p-anthraquinone with the objective of determining whether or not they proceed by a similar pathway. Results and discussion When 1,4-benzoquinone was allowed to react with hexamesitylcyclotrigermane, we obtained a mixture of a linear oligomer 2 having one organogermylene unit, a cyclic oligomer 3 and a surprising 1,3-cycloadduct 4, the formation of which was mentioned but that w a s no t identified. (Mes2Ge)3· CSH6 100°C — ο Ω Mes^ ι Gei Mes + Mes2Ge (1) m 2 : m = 1 3 : m = 2, η = 2 Compound 4.could be extracted from the reaction mixture after several recrystallizations from hexane, petroleum ether and ether, and was obtained pure in a 17% yield. In its H and 1 C NMR spectra, the two mesityl groups are not equivalent, as expected from the different environments of the germanium atoms, one attached to an oxygen atom and the other to a carbon atom of the aromatic ring. The H NMR spectrum of the aromatic system showed the expected coupling interactions of the three non-equivalent protons. An X-ray crystal structure study of compound 4 confirmed its 1,3-cycloadduct structure as shown by the ORTEP diagram in Figure 1. The two fiveand six-membered rings are in the same plane, but the heterocycle is highly distorted.

REACTIONS OF CYCLOTRIGERMANE WITH p-BENZOQUINONES: OLIGOMERS AND A NOVEL 1,3-CYCLOADDUCT