The reaction of tris(trimethylsilyl)silyllithium with dibenzosuberenone

Tris(trimethylsilyl)silyllithium (1) reacts with dibenzosuberenone in ether to give, after carbonyl addition of the lithium silanide and lithium trimethylsilanolate elimination according to a modified Peterson mechanism, the transient silene 5 which is trapped by addition of excess 1 at the Si=C double bond to afford 2-[5H-dibenzo[a,d]cyclohepten-5-yl]-1,1,1,4,4,4-hexamethyl-2,3,3-tris(trimethylsilyl)tetrasilane (7), When the same reaction is carried out in dimethoxyethane, no silene is generated, but after carbonyl addition of 1 at dibenzosuberenone a 1,3-Si,O-trimethylsilyl migration occurs, producing the lithium silanide 8 which undergoes an intramolecular addition at the 10,11-C=C double bond of the dibenzocycloheptatriene system under formation of a bicyclic organolithium derivative which reacts with excess dibenzosuberenone to afford the alcohol 10. Compounds 7 and 10 were fully characterized by their IR, NMR and MS data, for 10 the results of an X-ray crystal structure analysis are also given.