Vinylsilane intermediates

Ketones can be isomerized by a 1,2-carbonyl shift throu a vinylsilane intermediate (Scheme 12). The main products of ozonolysis of vinylsilanes are a-... 

The ability to promote /S elimination and the electron-donor capacity of the /3-metalloid substituents can be exploited in a very useful way in synthetic chemistry. Vinylstannanes and vinylsilanes react readily with electrophiles. The resulting intermediates then undergo elimination of the stannyl or silyl substituent, so that the net effect is replacement of the stannyl or silyl group by the electrophile. An example is the replacement of a trimethylsilyl substituent by an acetyl group by reaction with acetyl chloride. 

As a result of the excellent precedent from the Takeda and Smith groups, we targeted vinylsilane 136 as a key intermediate in a Brook rearrangement/conjugate... 

The use of tri-tert-butylphosphine has produced still higher selectivities, allowing near total control in the synthesis of (A)-vinylsilanes, including alkoxysilanes and disiloxanes.38,39 In the context of a total synthesis of an HMG-CoA reductase inhibitor, hydrosilylation with a chlorosilane catalyzed by a platinum(O) olefin complex, Pt2 [(CH2=CH)Me2Si]20 3 (also known as Karstadt s catalyst), followed by coupling with a 2,6-disubstituted aryl iodide forged a key intermediate shown in Scheme 6.38... 

Efforts to tune the reactivity of rhodium catalysts by altering structure, solvent, and other factors have been pursued.49,493 50 Although there is (justifiably) much attention given to catalysts which provide /raor-addition processes, it is probably underappreciated that appropriate rhodium complexes, especially cationic phosphine complexes, can be very good and reliable catalysts for the formation of ( )-/3-silane products from a air-addition process. The possibilities and range of substrate tolerance are demonstrated by the two examples in Scheme 9. A very bulky tertiary propargylic alcohol as well as a simple linear alkyne provide excellent access to the CE)-/3-vinylsilane products.4 a 1 In order to achieve clean air-addition, cationic complexes have provided consistent results, since vinylmetal isomerization becomes less competitive for a cationic intermediate. Thus, halide-free systems with... 

The preference for the /3-silyl isomer product complements methods available for hydrostannation of alkynes, for which the a-stannyl regioisomer is formed preferentially.70 7011 70c In addition, the /3-silyl products serve as the platform for a tertiary alcohol synthesis (Scheme 15). Upon treatment of vinylsilanes such as B with tetrabutylam-monium fluoride (TBAF) in DMF at 0 °C, a 1,2 carbon-to-silicon migration occurs, affording the tertiary heterosilane E. Oxidation of the C-Si bond then provides the tertiary alcohol. Good 1,2-diastereocontrol has been demonstrated for y-alkoxy substrates, as in the example shown. The studies suggest that the oxidation of the sterically demanding silane intermediate is facilitated by the intramolecular formation of a silyl hemiketal or silyllactone for ketone or ester substrates, respectively.71... 

Burke et al. [84] synthetised nagilactone F (55) by a polyenic cyclization initiated with acetal and concluded with vinylsilane, giving an overall yield of 6%. The key steps in this synthesis were the coupling of substrates 166 and 167 with control of the absolute and relative stereochemistry, the cationic biscyclization to form the intermediate tricyclic trans-anti-trans 169 and the formation of the D ring by regio-selective intramolecular remote functionalization. 

The silirane intermediate could also account for the formation of vinylsilane 89 when (trimethylsilyl)carbene is generated from dichloromethyl(trimethyl)silane and Na—K in a gas-phase reaction53. The transformations of (trialkylsilyl)carbenes, generated from (a-halomethyl)silanes by a-elimination with a strong base, may involve transient siliranes as well (equation 23 and Section III.E.l.b). 

The photolysis of the rigid l-silabicyclo[2.2.1]heptene 250, which may be regarded as a cyclic vinylsilane, induces a 1,3-carbon shift to produce a cyclic silene intermediate 251, which is trapped by alcohols to give 252 (equation 62)141 142. 

Disproportionation between vinylsilanes and monosubstituted alkenes catalyzed by ruthenium complex (equation 104) has been suggested to occur via a /1-silyl group elimination. The intermediate silylruthenium complex, RuCl(CO)(PPh3)2(SiMe2R1), has been characterized by spectroscopic means194. 

In the case of the (Z)-vinylsilane (Z)-146, the observed syn selectivity results from the cyclization of intermediate 149 in which the TMS group is already axially orientated due to the Z-double bond geometry of the precursor. 

Vinylsilanes are proper compounds which have won great appreciation as facile intermediates for many sorts of application. They are prepared either by addition reactions of acetylenes (vide supra) or by elimination reactions of saturated organosilanes. The main reactions, carried out with vinylsilanes, are addition reactions to obtain saturated organosilanes or electrophilic substitutions of the silyl group under Friedel-Crafts conditions where a rapid cleavage of the silyl moiety occurs (Scheme 8). 

As shown in Scheme 17,180 was available from the common, totally synthetic, intermediate 17. Using reported methodology for the introduction of vinylsilanes,57 17 was reacted smoothly with (methoxy dimethylsilyl) trimethylsilyl methyl-lithium in pentane to afford (EIZ) vinyl silane 220 in 54% yield. The main by-product in this reaction was ketone 17, which could be recycled thus, based on recovered 17, the yield of 220 was 93%. Hydrolysis of ketal 220 occurred without protodesilylation upon exposure to aqueous oxalic acid absorbed onto silica gel to give ketone 221 in 80% yield. Upon low-temperature ozonolysis of 221 in methanol, a remarkably stable dioxetane 223 was produced, as evidenced in the H NMR... 

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