A New Spirocyclic System:  Synthesis of a Silaspirotropylidene

A silaspirotropylidene, 5, has been obtained from the reaction of the lithium salt of tetramethylsilole dianion (3) with 2 equiv of diphenylcyclopropenone, followed by quenching with Me₃SiCl. The X-ray crystal structure of 5 indicates that the five-membered ring is planar and the silepine ring adopts a boat conformation.