Oxasilacyclopropane. Isolation and characterization

Versatile Reactivity of a Zwitterionic Isolable Silylene toward Ketones: Silicon‐Mediated, Regio‐ and Stereoselective CH Activation

“…Related intermediates of 2 with a non-aromatic siloxindane ring system have been previously proposed but could not be detected for similar reactions of transient silylenes [17,18] and a stable silylene [16] with benzophenone, respectively. A close example shows decamethylsilicocene which reacts slowly with benzophenone in toluene to give the corresponding analogue of 2.…”

“…[17] Its generation can be rationalized by a reaction pathway involving prior formation of donor-acceptor adduct C followed by intramolecular proton abstraction and enolization through the divalent Si atom (Scheme 5, pathway i). An alternative pathway to 5 is the formation of a 1,4-addition intermediate based on reaction of silylene 1 with the enol form of the acetophenone (Scheme 5, pathway ii).…”

“…In the latter case, merely one isolable Nheterocyclic silylene, [16] transient silylenes generated in situ either by thermolysis [17] or photolysis of the corresponding precursors, [18] and decamethylsilocene [19,20] were employed to study the reactivity of divalent silicon toward ketones. The conversions led to unexpected new SiÀC-and SiÀO-functionalized products, including siloxindanes [17][18][19][20] and silyl enol ethers, [17] depending on the electronic nature of the applied silylenes and the ketones. The mechanism is unknown and intermediates could not be observed but it has been proAbstract: Reactions of the isolable, ylide-like silylene LSi: 2 , Ar= 2,6-iPr 2 C 6 H 3 ) with different ketones (benzophenone, benzylideneaceton, acetophenone) have been investigated.…”

Structure of 2-(1-adamantyl)-2-trimethylsiloxy-1,1-bis(trimethylsily)-1-silaethylene

“…The O atom of the THF molecule is further from the Si atom, 1.878 (4) A, than the 1.58-1.67 A commonly found when Si is bonded to three C atoms and one O atom. (See, for example, Ando, Hamada, Sekiguchi & Ueno, 1982;Glidewell & Liles, 1978;Stensland & Kierkegaard, 1970). However such a long Si-to-O distance is not without precedence, a bond of the same length being present in a dibenzosilepin (Paton, Cody, Corey & Glick, 1976 …”

The Reactivity of a Silacyclopentadienylidene towards Aldehydes: Silole Ring Expansion and the Formation of Base‐Stabilized Silacyclohexadienones

“…It is well-known that silolyl anions have some degree of aromaticity because of the delocalization of the negative charge in the C 4 Si ring. [16] We assumed that the initially formed NHC-stabilized SiCO three-membered ring, originally proposed by Ando et al [17] and recently structurally authenticated by Roesky et al and Kira et al,[4a,b] is subject to CÀO bond cleavage of the strained SiCO ring to form a silolyl anion and an oxocarbocation. Electrophilic addition of the cation to the adjacent C=C bond, followed by complete C À O bond cleavage gives the bicyclic intermediate.…”