Silene, elimination-addition reaction

SILENE-TYPE SPECIES IN ELIMINATION-ADDITION REACTIONS... 

But till now only methods involving an in situ formation of deprotonated 1 have been described. In this paper we present a procedure leading to pure, isolated 1-hydroxyalkyl-polysilanes 1. In presence of base fliey are easily converted into transient silenes, which were characterized by various dimerization and addition reactions. The availability of isolated 1 in the synthesis of silenes according to the Peterson concept offers the possibility of a free choice of the solvent and the base used to initiate the silanolate elimination. With respect to the significance of the reaction medium for the silene generation and its subsequent reactions, this is of particular importance. 

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 silene . Among many reactions, it has been shown that the transient silene adds to anthracene to afford stCTeoisomCTs, 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. 

The formation of the a-metalated species in the case of the Auner/Jones Type silenes (neopentylsilenes) 132 (which is deduced by formation of dimers 133 or by trapping) is achieved through addition of f-butyllithium to a vinylchlorosilane in an inert solvent79,80. The initially formed lithiated intermediate eliminates LiCl at ca 0°C (equation 31), the exact temperature depends on the substituents R. The multitude of transient silenes that are available through this method will be discussed in Section I.B.4.b on the reactivity of neopentylsilenes. The basic reactions of Cl3Si—CH=CH2 with t-BuLi have... 

Three different routes to the key compounds for the sila-Peterson elimination, the a-alkoxydisilanes 157, are described in the literature, namely A, reaction of silyllithium reagents with ketones or aldehydes B, addition of carbon nucleophiles to acylsilanes C, deprotonation of the polysilylcarbinols. In addition, method D, which already starts with the reaction of 2-siloxysilenes with organometallic reagents, leads to the same products. The silenes of the Apeloig-Ishikawa-Oehme type synthesized so far are summarized in Table 4. 

The mechanism of the formation of the silanol 9 (Scheme 3) is understood as the result of an acid-catalyzed formal elimination of dimethylaminotrimethylsilane generating the silene 7, followed by the addition of H2SO4 at the silene double bond and subsequent hydrolysis of the silylsulfate 8. To our best knowledge, this is the first case of an acid-induced sila-Peterson reaction. 

The reactions of bare Fe" " ions and related species in the gas phase continue to attract much interest. The remote functionalisation of 1,6-hexanediol by Fe occurs by C-H activation at C(3) and C(4).26 Functionalisation of 3-methyl-2-pentanone at C(4) is diastereoselective, probably because of the conformation of a chair-like intermediate. Reactions of Fe with anisoles and phenols have also been studied.28 Interaction of Fe with silanes gives both silene and silylene species, though the two are not interconvertible. The reactions of Fe(alkene)+ complexes with pentane were found to differ dramatically from those of bare Fe" , and C-H and C-C activation were also observed in reactions of Fe(C2H4) with oxygen. 0,31 interaction of Fe(benzyne)+ with alkyl halides led to C-X or C-C addition followed by p-elimination and loss of HX.32 The gas phase reaction of Fe(NH2)Me" with C2H4 is best explained by insertion into the Fe-C bond followed by P-elimination and loss of propene. The reaction of FeMe with 1-octyne also leads to C-C bond forming processes. 

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