Silaheterocyclen. XI. Erzeugung und Cycloadditionsverhalten des Diphenylneopentylsilaethens, Ph₂Si=CHCH₂^tBu

Diphenylneopentylsilene, Ph₂Si=CHCH₂^tBu (3), is prepared as a reactive intermediate by the reaction of diphenylvinylchlorosilane (1) with Li^tBu in nonpolar solvents via the α-lithioadduct Ph₂Si(Cl)CH(Li)CH₂^tBu (2). This lithiated species can be trapped by trimethylsilyltriflate and yields silene 3 by 1,2-LiCl-elimination. Without suitable Si=C-trapping agents, the E / Z-isomeric tetraphenyl-2,4-dineopentyl-1,3-disilacyclobutane (6) is formed by cyclodimerization. In the presence of dienes like 2,3-dimethyl (DMB)- and 2-methyl-1,3-butadiene (MBD) the Diels-Alder and ene-products are formed in competition, while the cycloaddition of 3 with norbornadiene, cyclohexa-1,3-diene, cyclopentadiene and anthracene yields the [2+2+2]- or the [4+2] products exclusively. Exo / endo-{2,2-diphenyl-3-(2′,2′-dimethylpropyl)-2-silabicyclo[2.2.2]oct-5-ene} (19) is a crystalline solid as well as compound E-6, whose structures are presented in this paper.