Allyl tris silane

Allyl tris(trimethylsilyl)silanes are obtained in high yields from the reactions of unsubstituted and 2-substituted allyl phenyl sulfides with (TMS)3SiH... 

Reaction 7.74) [84], That is, (TMS)3Si radical added to the double bond of allyl sulfides, giving rise to a radical intermediate that undergoes (3-scission with the ejection of the thiyl radical. Hydrogen abstraction from the silane completes the cycle of these chain reactions. 2-Functionalized allyl tris(trimethylsilyl)si-lanes (71) have been employed in the radical-based allylation reactions. 

The radical source must have some functional group X that can be abstracted by trialkylstannyl radicals. In addition to halides, both thiono esters and selenides are reactive. Allyl tris(trimethylsilyl)silane can also react similarly.232 Scheme 10.11 illustrates allylation by reaction of radical intermediates with allylstannanes. 

Reactions of unsubstituted and 2-substituted allyl phenyl sulphides with (TMS SiH provided the corresponding allyl tris(trimethylsilyl)silanes (112) in high yields... 

Chatgilialoglu and Curran synthesized a variety of allyl tris(trimethylsilyl)silanes bearing substituents at the 2-position (Scheme 26) [70], These allylsilanes underwent reaction with alkyl halides when heated with a radical initiator to give very good yields of allylated products. The reactions were relatively sensitive to electronic effects electrophilic radicals reacted well only with electron-rich allyl silanes and vice versa. One potential drawback of this methodology is that the reactions reported were all carried out at 80 °C or above, suggesting that relatively high temperatures are necessary for efficient reaction. 

Allyl[tris(trimethylsilyl)]silanes. These valuable synthetic reagents are prepared by free-radical substitution of allyl phenyl sulfides with (MejSiljSiH. They can be used as radical-based allylating agents. 

A recent example of this reaction has been reported which allows for the preparation of 2-functionalized allyl tris(trimethylsilyl)silanes (equation (38)) [83], a new class of radical-based allylating agents [84]. 

Ueno has devised a general synthetic method for the preparation of allyltin from allyl sulfones via an Sh2 process [131]. The key steps for these transformations which consist of addition of stannyl radical to appropriate allyl sulfone and the -elimination of sulfonyl radical are depicted in Scheme 17 (see Scheme 11 for detailed propagation steps). Since both steps are reversible, the equilibrium can be driven to the left or right depending on the experimental conditions [132]. However, the extension of this methodology to the synthesis of homoal-lylic alcohols or to 2-substituted-1,3-butadiene have been achieved starting from the appropriate sulfone (Scheme 17) [133]. This approach has also been applied to the preparation of 2-functionalized allyl tris(trimethylsilyl)silanes (cf. equation (38)) [83]. 

Diastereoselective syntheses of dihydrobenzo[f>]furans have been accomplished by a rhodium-catalyzed regioselective and enantiospecific intermolecular allylic etherification of o-iodophenols as a key step, providing the corresponding aryl ally ether 122, which leads to a dihydrobenzo[b]furan by treatment of the intermediate aryl iodide with tris(trimethylsilyl)silane and triethylborane at room temperature in the presence of air <00JA5012>. 

The combination of allylic amination, ring-closing metathesis, and a free radical cyclization provides a convenient approach to the dihydrobenzo[b]indoline skeleton, as illustrated in Scheme 10.10. The rhodium-catalyzed aUylic amination of 43 with the lithium anion of 2-iodo-(N-4-methoxybenzenesulfonyl)arrihne furnished the corresponding N-(arylsulfonyl)aniline 44. The diene 44 was then subjected to ring-closing metathesis and subsequently treated with tris(trimethylsilyl)silane and triethylborane to afford the dihydrobenzojhjindole derivative 46a in 85% yield [14, 43]. 

This methodology was applied to a two-step sequence for the preparation of enantio-merically enriched dihydrobenzo[h]furans (Scheme 10.11) [46]. Rhodium-catalyzed allylic etherification of (S)-47 (>99% ee), with the sodium anion of 2-iodo-6-methyl-phenol, furnished the corresponding aryl allyl ethers (S)-48/49 as a 28 1 mixture of regioisomers favoring (S)-48 (92% cee). Treatment of the aryl iodide (S)-48 with tris(trimethylsilyl)silane and triethylborane furnished the dihydrobenzo[h]furan derivatives 50a/50b as a 29 1 mixture of diastereomers [43]. 

Reaction with nitrogen tettoxide produced very unstable nitro-nitrates. On two occasions violent explosions took place in USRubberCo Laboratory at Passaic, NJ Note [n view of remarkable instability of nitrated derlvs of silanes and obvious force of detonation, it. is suggested to use mono-, di-, tri-, and tetra-allylic silanes and nitrogen tetroxide in liquid rocket propellants. It is also likely that vinylsilanes will exhibit similar behavior... 

Tris(trimethylsilyl)silyl radical is relatively stable and can therefore serve as a radical leaving group. This reaction has been extended to the radical-initiated allylation of organic halides202 203. Thus, thermolyses of bromides a to a carbonyl substituent 144 or of simple iodides with allyltris(silyl)silane in the presence of a radical initiator gives the corresponding allylation products (equation 112). 

The radical-initiated allylation of alkyl halides with allyltris(trimethylsilyl)silanes proceeds via an SH2 process mediated by a tris(trimethylsilyl)silyl radical.225 The radical-allylating agents react with alkenes, alkynes, and aldehydes via a radical chain process to give the corresponding allylsilylation products.226... 

Allyl silanes react with a wide variety of electrophiles, rather like the ones that react with silyl enol ethers, provided they are activated, usually by a Lewis acid. Titanium tetrachloride is widely used but other successful Lewis acids include boron trifluoride, aluminium chloride, and trim ethyls ilyl tri-flate. Electrophiles include the humble proton generated from acetic add. The regiocontrol is complete. No reaction is observed at the other end of the allylic system. All our examples are on the allyl silane we prepared earlier in the chapter. 

In the reaction using cadmium promoter, the selectivity for tris(chloro-silyl)methane 8b was the highest among the four tris(chlorosilyl)methanes 7b-10b and about 73% in the distribution of their four compounds. These are consistent with the results observed for the direct reactions of silicon with (chloromethyl)silanes,20,21 allyl chloride,27 methylene chloride,22 and chloroform.23... 

Ti-F bond [182.5(5) pm], which as expected is shorter than the Ti-Cl bond of 17 [228.4(3) pm] [12]. We were of course interested in the catalytic properties of 24 in comparison with triflate 23. In the presence of 23, allylsilane 5 adds smoothly to benzaldehyde the product is, however, racemic. Most probably the catalyst is tri-methylsilyl triflate, which is formed according to pathway B (Scheme 2, cf. [4a]). On the contrary, no reaction between benzaldehyde and allyl silane 5 is observed in the presence of fluoride 24. As we observed earlier, all cyclopentadienyltitanium TADDOLates studied catalyzed the conversion of benzaldehyde 25 with salt-free (i-PrO),TiCH3 26 to 2-phenylethanol 27 [11]. In this case the titanium fluoride effect was indeed very pronounced, as at -78 °C 0,5 % of 24 afforded 60 % of product 27 in 17 h with 78 % ee with 2 % of 24 the induction is 93 % ee. 

An early study of the allylation reactions of oxocarbenium systems has been described by Danishefsky for synthesis efforts directed towards indanomycin. The reactions of ( )-and (Z)-2-butenylsilanes silanes are the focus for this report. However, the study also examined reactions of the (E,Z)-mixture of 2-butenyl-tri-n-butylstannanes with tri-o-acetyl-o-galactal 132 at -30 °C, in the presence of BF3 OEt2... 

Chatgilialoglu and Curran have found that allyltris(triniethylsilyl)silanes react with a variety of alkyl halides to provide allylation products via an Sh2 process mediated by the tris(trimethylsilyl)silyl (TTMSS) radical (Scheme 10.199) [523]. In this system the allylsilanes work as radical-allylating agents and TTMSS radical sources. We have used the reactivity of allyltris(trimefhylsilyl)silanes for allylsilyla-tion of alkenes and alkynes via a radical chain mechanism (Scheme 10.199) [524]. 

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