Silylmethyl allylic silanes

Scheme 7.21. Formation of silylmethyl allylic silanes from gem-disubstituted homoallylic ethers.

From these observations, Woerpel and Cleary proposed a mechanism to account for allylic silane formation (Scheme 7.23).85 Silacyclopropane 94 is formed from cyclohexene silacyclopropane 58 through silylene transfer. Coordination of the Lewis basic benzyl ether to the electrophilic silicon atom86-88 generates pentacoordinate siliconate 95 and increases the nucleophilicity of the apical Si-C bond.89 Electrophilic attack by silylsilver triflate 96 forms silyl anion 97. Intramolecular deprotonation and elimination then affords the silylmethyl allylic silane. 

Scheme 5.22 One-pot synthesis of 2,3,5-trisubstituted tetra-hydrofurans with a-silylmethyl allylic silane.

Allylsilanes result from allyl sulphides which have siloxy subsdtuents with regio and stereochemically using allyl-lithium, from alkenyl Fischer carbene complexes with silanes through addition of Si-H to the carbene, and opdcally active y-silylallylamines result frnn a n-allylPd intermediate obtained from the carbonate using amines or azide, while allyldichlorosilane can be prepared by the direct method at 220 - 320 C as the main product. The protodesilyladon of allylsilanes provides a route to vinyl sulphones while silylmethyl allyl sulphones result from silylmethyl cuprates and sulphonylalka-1,2-dienes, and are used in the... 

Monosubstituted diene systems have been employed for the synthesis of bicyclic systems as well as monocyclics [17]. The simplest way to accomplish this is to construct a second ring onto an existing structure (Eq. 54). This cyclization process is initiated at the alkene lacking allylic substitution. The formation of the six-membered ring necessitates the use of methylphenylsilane as the silylat-ing reagent. Because the silane itself comprises a new stereocenter, it must be removed by oxidation to assess accurately the diastereoselectivity of cyclization. Fluxionality of the five-membered ring results in a mixture of diastereomers at the silylmethyl-substituted stereo center. 

---