The chemistry of three-and four-membered ring systems consisting of Group 14 elements heavier than carbon is a subject of considerable interest. [1] The thermal and photochemical conversion of cyclotrigermanes into digermenes and germylenes is well established and has been used for the synthesis of a variety of novel germanium compounds. [2] However, cyclotrigermane derivatives incorporating a bicyclic system are completely unknown for synthetic reasons. [3, 4] Most of the cyclotrigermane derivatives were synthesized by the simple reductive coupling reaction of the corresponding diorganodihalogermane with the appropriate reducing agents. [1, 2] Recently, we succeeded in synthesizing a variety of cyclotrigermene analogues of cyclopropene by reaction of the cyclotrigermenium ion with nucleophiles. [5] The reactivity of the cyclotrigermenes is of special interest, since cycloaddition to the endocyclic Ge Ge bond could provide access to new bicyclic compounds. We now report the synthesis of the first bicyclic cyclotrigermane derivatives by the reaction of a mesityl-substituted cyclotrigermene with isoprene, 2,3-dimethyl-1,3-butadiene, and phenylacetylene.
After the successful synthesis of tetrakis(tri-tert-butylsilyl)cyclotrigermene (tBu 3 Si) 4 Ge 3 (1 a) [6] and tetrakis(tri-tert-butylgermyl)cyclotrigermene (tBu 3 Ge) 4 Ge 3 (1 b) [6] by reaction of GeCl 2 (dioxane) with tBu 3 SiNa or tBu 3 GeLi, we presumed that the cyclotrigermenes should be suitable as precursors of reaction mixture was stirred for 1 h before it was allowed to warm to ambient temperature. After the mixture had been stirred for a further 24 h, a cloudy yellow/brown solution was produced. The mixture was filtered through Celite, cooled to Γ 20 8C, and left to stand for 12 h, resulting in the precipitation of small, colorless crystals of 1.