Silenes neopentyl

Reactions favoring [2 + 2] cycloaddition tended to be those that had strongly electronegative groups on the sp2-hybridized silicon but only H and the neopentyl group on the sp2-hybridized carbon atom. Butadiene and cyclohexadiene generally favored [2 + 2] cycloaddition with these silenes. The [2 + 2] adducts with cyclohexadiene appear to be kinetic products, since they cleanly isomerized to the Diels-Alder adducts over time.182... 

Jones and coworkers developed a new method of generating silenes based on the addition-elimination reaction. Addition of t-BuLi to an appropriately substituted chloro(vinyl)silane produces a neopentyl-substituted silene67,68. Among many reactions, it has been shown that the transient silene adds to anthracene to afford stereoisomers, 40a and 40b, as isolable compounds (Scheme 11). Fractional crystallization of the adduct 40 from hexane gave pure 40a, leaving a 69/31 mixture of 40a and 40b. 

A stable neopentylsilene, 1,1-dimesity 1-2-neopentyl-1-silene 134, was synthesized by the Couret group from fluorodimesitylvinylsilane and t-BuLi82. It was characterized by NMR spectroscopy. 

In one series of experiments the a-lithiated silanes were produced by a nucleophilic addition of tert-butyllithium to the C=C double bond of a vinylhalosilane so that the 1,2-elimination led to a silene carrying a neopentyl substituent on the unsaturated carbon... 

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