Synthesis of Spirocyclosiloxanes by Flash Vacuum Pyrolysis of 2,7-Dimethyl-2,3:7,8-Diepoxy-5-Silaspiro(4.4)Nonane and Cyclosiloxanes

摘要

Flash vacuum pyrolysis (FVP) of 2,7-dimethyl-2,3:7,8-diepoxy-5-silaspiro4-nonane with cyclotetra- or cyclopenta-siloxanes (D sub 4 or D sub 5) leads to products which apparently result from transannular insertion of (0=Si=0) or an equivalent synthon into Si-O single bonds of D sub 4 or D sub 5: 2,4,6,8,10-pentasila-1,3,5,7,9,11-hexaoxa-spiro(5.5)undecane (D sub 2 QD sub 2) and 2,4,6,8,10,12-hexasila-1,3,5,7,11,13-heptaoxa-spiro(5.7)tridecane (D sub 3 QD sub 2) respectively. The scope of this reaction has been explored with substituted cyclotetrasiloxanes such as heptamethylcyclotetrasiloxane, vinylheptamethylcyclotetrasiloxane, phenylthepthamethylcyclotetrasiloxane, and chloromethylheptamethylcyclotetrasiloxane. In all cases substituted spirocyclosiloxane products (D sub 2 QDD supercript x) were obtained. Silicon 29 NMR has proved particularly useful for the assignment of structure of these spirocyclosiloxanes.