Migration of silyl groups

We suggest that the ejected thiyl radical undergoes a fast 1,2-migration of silyl group from silicon to sulfur (Reaction 85), affording a new silyl radical that either reacts with (TMSlsSiH (Reaction 86) which completes the reaction cycle, or replaces the (TMSlsSi radical in the above described reaction sequence. 

The reaction of silylborane with 1-halo-l-lithio-l-alkenes yields 1-boryl-l-silyl-l-alkenes via borate formation followed by 1,2-migration of silyl group (Equation (90)).76,240 The mechanism seems to be closely related to that proposed for the silaboration of isocyanide (Figure 2). Vinyl-substituted carbenoids, l-chloro-l-lithio-2-alkenes, react with silylpinacolborane to give l-boryl-l-silyl-2-alkanes in good yield (Equation (91)).241 This methodology is applied to the synthesis of l-boryl-l-silyl-2-cyclobutene.2 2 Similar reactions are carried out with other carbenoid... 

Examples of 1,2 migration of silyl group from silicon to other atoms are also well documented. Reaction (6.21) that involves a transfer from silicon to carbon has been observed in the gas phase at elevated temperatures [35], From the measured Arrhenius parameters, i.e. logA/s = 12.3 and = 90kJ/mol, it is clear that the reaction is unimportant around room temperature. However, this type of reaction is probably the essential step in the formation of silicon-carbon fibres by pyrolysis of methylpolysilanes. 

Metal-promoted 1,2-migration of silyl groups in silylalkynes results in the formation of silylvinylidenes which are subsequently readily desilylated. " Alkynyl-substituted silylvinylidenes have been obtained from silylated diynes and the Fe(N2)(CO)2 P(OMe)3 2/ Fe(CO)2[P(OMe)3]2 2(/t-N2) reagent and similar species are implicated in the reactions of several Group 8 metal complexes with mono- and bis-trialkylsilyl diynes. " ... 

On the other hand, an intermolecular migration of silyl groups also takes place among 5-methyl-2-(trialkylsilyl)thiophenetricarbonylchromium(0) complexes under basic conditions45. Increased steric hindrance from the silyl groups (see entry 34 of Table 1) results in preferential deprotonation. 

Migration of silyl groups from a- to /3-oxygen in a sodium aldol reaction has been... 

Facile migration of silyl groups in 5-silylcyclopentadienes is usually referred to as fractional 1,2-silyl rearrangement or 1,5-suprafacial silatropic rearrangement (equation 39). The fundamentals of this migration have been well discussed in BB1. Several examples of this type of migration have also appeared in recent papers95-105. 

Migration of Silyl Groups, 166 Trimethylsilyl, 171 Triethylsilyl, 178 Triisopropylsilyl, 183 Dimethylisopropylsilyl, 187 Diethylisopropylsilyl, 187 Dimethylthexylsilyl, 188 2-Norbornyldimethylsilyl, 189 f-Butyldimethylsilyl, 189 f-Butyldiphenylsilyl, 211 Tribenzylsilyl, 215 Tri-p-xylylsilyl, 215 Triphenylsilyl, 215 Diphenylmethylsilyl, 216 Di-f-butylmethylsilyl, 217 Bis(f-butyl)-l-pyrenylmethoxysilyl, 218 Tris(trimethylsilyl)silyl Sisyl, 218 (2-Hydroxystyryl)dimethylsilyl, 219 (2-Hydroxystyryl)diisopropylsilyl, 219 f-Butylmethoxyphenylsilyl, 219 f-Butoxydiphenylsilyl, 220... 

Brook rearrangement in tandem bond formation strategies (formation of heterocycles as the result of C —> O or O — C migrations of silyl groups) 01T2065. 

B. Migrations of Silyl Groups to Electron-deficient Centres. 466... 

The interaction of 2-cyanomethyl-4,5-dimethyl-l,3,2-dioxaphospholan 2-oxide and hexamethyldisilazane produces a complex system of products which involves ring-chain tautomerism and migrations of silyl groups from N to O. In the solid phase the product has the structure (126) but, in solution, the pentaco-ordinate structure (125) predominates, although, depending on the actual solvent, structures (127) or (128) are discernible by means of i.r. spectroscopy. ... 

However, the chemical results alone indicate that migration of silyl groups from O to N is very rapid in hydroxylamine anions. The results of quenching experiments at -78°C show that the half-life for rearrangement cannot be more than a few minutes at this temperature. 

The reaction of acylsilanes with a-sulfinyl carbanions proceeds through the initial formation of an a-silyl alkoxide intermediates (5), followed by the cationotropic migration of silyl group to oxyanion and the elimination of sulfenate ion, to afford the corresponding silyl enol ethers (Scheme 3). ... 

The gold-catalyzed cyclization of (< -alkynylphenylthio)silanes 51 produced the corresponding 3-silylbenzo[b]thiophenes 52 in good to excellent yields (Scheme 27.20) [25]. It was proven that the migration of silyl group proceeds in an intermolec-ular manner by crossover experiments. 

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