SYNTHESIS OF SPIROCYCLOSILOXANES BY FLASH VACUUM PYROLYSIS OF 2,7-DIMETHYL-2,3:7,8-DIEPOXY-5-SILASPIRONONANE AND CYCLOSILOXANES

Article abstract of DOI:10.1016/S0022-328X(00)99534-2

Flash vacuum pyrolysis (FVP) of 2,7-dimethyl-2,3:7,8-diepoxy-5-silaspiro<4.4>nonane with cyclotetra- or cyclopenta-siloxanes (D₄ or D₅) leads to products which apparently result from transannular insertion of or an equivalent synthon into Si-O single bonds of D₄ or D₅: 2,4,6,8,10-pentasila-1,3,5,7,9,11-hexaoxaspiro<5.5>undecane (D₂QD₂) and 2,4,6,8,10,12-hexasila-1,3,5,7,9,11,13-heptaoxaspiro<5.7>tridecane (D₃QD₂) respectively.The scope of this reaction has been explored with substituted cyclotetrasiloxanes such as heptamethylcyclotetrasiloxane, vinylheptamethylcyclotetrasiloxane, phenylheptamethylcyclotetrasiloxane, and chloromethylheptamethylcycloterasiloxane.In all cases, substituted spirocyclosiloxane products (D₂QDD^x) were obtained. 29Si NMR has proved particularly useful for the assignment of structure of these spirocyclosiloxanes.