SILAHETEROCYCLES .25. (ME3SIO)2SI=CHCH2TBU - A SILOXY-FUNCTIONALIZED SYNTHETIC EQUIVALENT FOR DICHLORONEOPENTYLSILENE

(Me3SiO)2Si=CHCH2tBu (4) is obtained by the reaction of (Me3SiO)2Si(CI)CH=CH, (2) with LitBu. The reaction proceeds via the alpha-lithiated species 3, which can be intercepted by trimethylsilyl triflate to give 5. Silaethane 4 dimerizes to the E/Z-isomers of disilacyclobutane 7 and adds to Me3SiOMe give 6. The reactivity of 4 resembles that of Cl2Si=CHCH2tBu (1): A [4 + 2] cycloadduct is obtained from the reaction with anthracene, and with 1,3-cyclohexadiene and 1,3-cycloheptadiene mixtures of monosilacyclobutanes (10 and 12) and bicyclic Diels-Alder adducts (9 and 11) are available. Exclusive [2 + 2] cycloaddition reactions take place with styrene (formation of 13), 2,3-dimethyl-1,3-butadiene (-->19), and 1,3-butadiene (-->21). With quadricyclane only the product (14) originating from a [2 + 2 + 2] cycloaddition is formed, while with 2,5-norbornadiene the [2 + 2] and [2 + 2 + 2] cycloadducts (14 and 15) are formed. In addition the ene products (16, 18, 20, 22) are isolated in some cases from side reactions. The tendency of 1 and 4 to preferably participate in [2 + 2] cycloaddition reactions is ascribed to the polarity of the Si=C bond and the additional influence of the pi donor ligands at silicon. These factors enable a stepwise [2 + 2] reaction in which the primary zwitterionic intermediates B are cyclized to yield the SiC four-membered ring compounds.