Silyl-substituted germenes. The reactions of germenes generated thermally from acyltris(trimethylsilyl)germane with conjugated enones

The cothermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)germane (1 and 2) with methyl vinyl ketone and acrolein at 120 degrees C gave the respective six-membered ring compounds, 2-tri-methylsiloxy-3,3-bis(trimethylsilyl)-3-germa-1-oxacyclohex-5-ene derivatives, arising from formal [2 + 4] cycloaddition of germenes with enones, along with appreciable amounts of the unchanged starting compounds. Similar thermolysis of 1 and 2 with methyl vinyl ketone and acroleinat 130 degrees C afforded two types of the products, [2 + 4] cycloadducts and acylbis(trimethylsilyl)germanes arising from the ring-opening reaction of the resulting cycloadducts, respectively. When 1 and 2 were heated in the presence of the same enones at 140 degrees C, acylbis(trimethylsilyl)germanes were obtained as the main products. The thermolysis of acylbis(trimethylsilyl)germane (3) with 2,3-dimethylbutadiene produced two stereoisomers of [2 + 4] cycloadducts. The results of theoretical calculations for the formation of germenes and [2 + 4] cycloaddition of the germenes to enones, and also isomerization of the resulting [2 + 4] cycloadducts, leading to the ring-opened products have also been reported. (C) 2010 Elsevier B.V. All rights reserved.