1.4- Disilyl-2-butenes

Reaction of 1 and related silyl anions with 1,3-dienes gives 1,4-disilyl-2-butenes. The (E)-isomer is the exclusive or major product. HMPT or 1,3-dimethyl-2-imidazolidinone (DMI) is essential. 1,3-Dienes substituted at C, and/or C4 do not undergo this reductive disilylation. 

Unsymmetrically substituted 1,4-disilyl-2-butenes undergo selective acylation, with the trimethylsilyl group being replaced in preference to triphenylsilyl (equation 20)7 ... 

A similar procedure has been employed to silylate the dianion of 3-methyl-3-buten-2-ol (67% yield).In systems where such internal activation is not possible (e.g. 2-raethyl-2-cyclohexen-l-o1), dianion formation can be performed in hexane to give a 75% yield of the corresponding disilyl compound. 

A dimerization reaction of alkenylmagnesium reagents in the presence of chlorosilanes, catalyzed by Cp2TiCl2, furnishing l,4-disilyl-2-butenes has been reported. Transition-metal-catalyzed carbon-carbon bond formation, promoted by Mn, Cr, Fe and Co, has been reviewed. ... 

The 1,2-dihydrodisilane (66) reacts with 2,3-dimethylbutadiene, in the presence of a Ni catalyst, to give both the normal hydrosilylation product and (Z)-l,4-disilyl-2-butene (Scheme 10). The nickel catalyst is assumed to be reduced to nickel(O), which oxidatively adds to the Si—Si bond of (66) in competition with addition to the Si—H bond. ... 

Titanocene dichloride catalyzes the reduction of alkyl, aryl, and vinyl bromides, aryl chlorides, alkoxy- and halosilanes ketones, esters, and carboxylic acids with alkyl Grignard reagents. This Cp2TiCl2/RMgX system can also be used for the hydromagnesation of alkynes, dienes, and alkenes (Section 3.2.5). Kambe et al. have reported a new type of titanocene-catalyzed transformation with vinyl Grignard reagents and chlorosilanes to furnish l,4-disilyl-2-butenes, as shown in Scheme 3.43 [31]. 

Reachons of 1,3-dienes with disilanes have been known to yield either 1 1 or 1 2 addihon products, depending on the choice of catalysts and disilanes. For example, NiCl2(PEt3)2 catalyzes 1,4-addihon of the Si-Si bond to 1,3-diene to produce l,4-disilyl-2,3-butenes [180], while the use of Pd(dba)2 as catalysts afford bis-silylahve dimerizahon products with high regio- and stereoselectivity (Eq. 2.77) [181]. 

E)-l-Phenyl-2-buten-l-one added to a little dichloro[( + )-2,2 -bis(diphenylphos-phino)-l,r-binaphthyl]palladium(II) and 2 eqs. 1,1-dichloro-l-phenyl-2,2,2-tri-methyldisilane in benzene at room temp, under N2, the mixture refluxed for 2 h, cooled to —70°, treated with 1.9 M methyllithium in ether, stirred for 10 min then quenched with dil. HCl (S)-l-phenyl-3-(phenyldimethylsilyl)butan-l-one. Y 72% (87% e.e.). F.e. and conversion to p-hydroxyketones, also z //-a-alkyl-j3-hydroxy-derivs. by asym. 1,4-disilylation-alkylation, s. T. Hayashi et al., J. Am. Chem. Soc. 110, 5579-81 (1988) without asym. induction using Pd(PPh3)4 s. Tetrahedron Letters 29, 4147-50 (1988). 

Trimethylsilyl Anion. Treatment of hexamethyldisilane (1) with an alkyllithium, metal alcoholate, or fluoride ion generates the trimethylsilyl anion (2) (eq 1). Reaction of (2) with aryl halides gives trimethylsilylarenes in 63-80% yields along with reduced products (ArH, 4-27%). tetra-w-butylammonium Fluoride (TBAF) catalyzed reaction of MegSi2 with butadienes gives l,4-disilyl-2-butenes (15-81% yield) with high ( ) selectivity. ... 

---