Allyl bromide Allyltrimethylsilane

Jurczak and Kiegiel reported that additions of allylmagnesium chloride and allyl bromide in the presence of Zn to iV-methyl and W-phenylglyoxyloyl-(2R)-borane-10,2-sultam occurred in a diastereoselective manner. Similarly, the Lewis acid mediated addition of allyltrimethylsilane also gave good diastereoselectivity and in the case with TiCU a change of direction of asymmetric induction was observed <99TL1009>. 

Guindon investigated diastereoselective allylation reactions of alkyl halides and phenyl selenides using allylsilanes [68], For example, substrate 116 is allylated by allyltrimethylsilane in the presence of magnesium bromide diethyl etherate using triethylboranc as an initiator (Scheme 25). No tin is required in these reactions. 

The magnesium-mediated reductive trifluoromethylation also works for other structurally diverse chlorosilanes. Chlorotriethyl-silane, f-hutyldimethylsilyl chloride, and tris(trimethylsilyl)silyl chloride have been applied to prepare corresponding trifluoro-methyl-containing silanes. However, the reductive trifluoromethylation did not take place with other electrophiles such as aldehydes, ketones, allyl bromide, benzyl chloride, or tributyltin chloride. Even tributyltin hydride and allyltrimethylsilane showed no reactivity The reason for such behavior is not clear. Probably, chlorosilanes play an important role during the reductive trifluoromethylation both as a silylating agent and a single-electron transfer promoter. 

Reaction with Allylic and Benzylic Electrophiles. The acyl radicals can be trapped with halogen- and silicon-based electrophiles. a -Allylation of a, -unsaturated ketones is done while using Mn(OAc)3 dihydrate and allyl bromide in refluxing benzene (eq 29). Better yields are usually observed for cyclopen-tenones compared to cyclohexenones. a -Benzylation is also possible using benzyl bromide as the electrophilic partner (eq 30). Both methods tolerate a range of substitution, including 8-alkoxy-a, -unsaturated ketones. It is possible to perform a sequential allylation/cyclization with an excess of allyltrimethylsilane (eq 31). Mn(OAc)3 offers good conversions, but the use of ceric ammonium nitrate (CAN) as co-oxidant improves yields. 

The direct allylation of 2-phenylpropanal proceeds with much lower selectivity [2-propenylmagnesium bromide 73 27 allyltrimethylsilane/titanium(IV) chloride 67 33]27. 

Jung and Maderna have reported the microwave-assisted allylation of acetals with allyltrimethylsilane in the presence of copper(I) bromide as promoter (Scheme 6.77b) [162]. Stoichiometric amounts of copper(I) bromide are required and the reaction works best with aromatic acetals free from strongly electron-withdrawing substituents on the aromatic ring. 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

Treatment of enantiomerically pure cyclic sulfonimidates 6 and 7 with allyllithium or allylmagnesium bromide gives optically active allylic sulfoximines 8 and 9 (R = allyl) as described in Section II.A.13 The reactions of /V-phenyl-S-(methyl-phenyl)sulfoximidoyl chloride 109 with allyltrimethylsilane or allyltributylstan-... 

Reaction of 142 with trimethylsilyl cyanide and allyltrimethylsilane under SnCl4 catalysis yields the tris(cyanide) 147 and the tris(allyl)tribenzotri-quinacene 148 [98]. Substitution of the bromine atoms takes place very efficiently by treatment of 142,145 and 146 with trimethylaluminum, to give trime-thyltribenzotriquinacene 149 and the tetraalkyl-substituted analogues 150 and 151, respectively, in excellent yields (>90%) [100]. Whereas reaction of 142 with triethylaluminum gives rise to complete reduction to 7, use of ethylmagnesium bromide affords 152 in low (20%) yield. A variety of further carbon-bonded sub-... 

Trimethylsilyl iodide is known to convert alcohols into iodides but is very sensitive to hydrolysis, so some new mild methods have been developed for the in situ generation of this reagent under neutral conditions. The reaction of allyltrimethylsilane and iodine does generate MeaSil, but the allyl iodide byproduct is not compatible with the presence of nucleophilic groups. A better solution is to use the bisallylic silane (58) and iodine (Scheme 38), where the other product is benzene. Trimethylsilyl bromide, although much less electrophilic... 

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