Silacyclopropanes pyrolysis

The extrusion of silylenes by pyrolyzing silacyclopropanes provides one of their more interesting reactions. Silacyclobutanes generate equally novel pyrolysis products. 

A 1-methoxy-l-silacyclopropane intermediate 70 has been suggested in order to explain the formation of l-methoxy-3,4-dimethyl-l-silacyclopent-3-ene. Vacuum pyrolysis of l,2-diethyl-l,l,2,2-tetramethoxydisilane in the presence of 2,3-dimethyl-l,3-butadiene, at 400-500°C and 10 torr, in a vertical quartz tube, produces 1-ethyl-l-methoxy-, 1-ethyl-, and l-methoxy-3,4-dimethyl-l-silacyclopent-3-ene. The 1-methoxy-l-silacyclopro-pane intermediate has been suggested in order to explain the formation of l-methoxy-3,4-dimethyl-l-silacyclo-pent-3-ene along with ethyltrimethoxysilane. Product 71 was obtained via the proposed silacyclopropane intermediate 70 (Scheme 18), while the other products proceed via an oxasilacyclopropane intermediate <1997JOM219>. 

Pyrolysis of 1,2-dimethyltetramethoxydisilane at 350 ""C gave methoxymethyl-silane which reacts with cis,cis-cyclo-octa-l,3-diene to give the silacyclopropane (173) which rearranges under the reaction conditions to give 1-methoxy-1-methyl-1-silacyclonona-2,8-diene by a free-radical cleavage of the C-1—C-8 bond and trans-annular hydrogen transfer. ... 

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