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UV photolysis of diazo(pentamethyldisilany1)methyl ketones 1 b -d generates acylsilenes (3-0x0-1-sila-1-propenes) 3 as reactive intermediates, which can be trapped by enolizable carbony1 compounds in an ene-type reaction. With non-enolizable carbonyl compounds or ethyl acetate, they undergo a [4 + 21 cycloaddition. In contrast to the photolysis in the absence of these carbonyl compounds, a Wolff rearrangement of 1 b -d (or the derived carbenes) to silyl ketenes 5b-d is observed as a competitive reaction.Acylsilenes (3-0x0-1-sila-1-propenes) 3 are reactive intermediates, which can be generated from pentamethyldisilanyl-substituted diazocarbonyl compounds 1 on the carbene route. In the absence of trapping reagents, subsequent reactions of 3 take place. Thus, photolysis of 3a -d in benzene yields cyclic isomers (of 3a,b) of [4 + 41 cyclodimers (of 3c,d) as the major products's2). An acylsilene-silylketene rearrangement is the exclusive reaction pathway in both gasphase thermolysis and solution photolysis of ethyl diazo-(pentamethyldisilany1)acetate (1 e)3). In general, silaethenes readily react with various kinds of carbonyl compounds4'. 3-Silaacrylate 3e is no exception since it can be trapped by enolizable (ene reaction ' 3 ' ) ) and non-enolizable ketones ([4 + 21 cycloaddition6), [2 + 21 cycloaddition followed by fragmentation of the 1,2-silaoxetanes thus f~r m e d~.~) ) ; however, the rearrangement to a silylketene remains the dominant reaction pathway. On the other hand, the fast cyclization of adamantyl-substituted acylsilene 3a prevents any intermolecular reaction with carbonyl compounds such as acetone and benzophenone lbJ.In this paper, we show that the behavior of 3a is an exception, since acylsilenes 3b-d can be trapped by both enolizable and non-enolizable carbonyl compounds.

Eine neuartige Bis(diazo)verbindung, ein stabiles elektronenreiches [4] Radialen und ein ungewöhnliches pentacyclisches Polyketal, das ist die Ausbeute dieser Arbeit. Das Silan 1 liefert bei der katalytischen Zersetzung den Tricyclus 2 mit einem Faltungswinkel des Vierrings von 35.0°, und aus 2 geht bei saurer Hydrolyse das Tetra(oxahomo)cuban 3 hervor.