Addition allyl siliconates

By an analogous route, the cyclization of chiral (z-amino imines 197, bearing the proper tw-functionality in the o -alkyl chain, will lead to 3-substituted 1,2-diaminocycloalkanes 198. The intermolecular and intramolecular addition of allylic silicon and tin compounds to a-amino azomethine compounds should also be investigated. 

Allyl glyddyl ether is a monoglycidyl derivative, used as a reactive epoxy diluent for epoxy resins. As an impurity, it was considered as the sensitizing agent in a plastic industry worker allergic to 3-glycidyloxy-propyltrimethoxysilane, an epoxy silane compound used as a fixing additive in silicone and polyurethane. 

Allyl esters of saturated acids have been extensively studied because of the potential application as a silane coupling agent. The addition of silicon hydrides to allyl chloroformate, allyl carbonate, allyl formate, and allyl acetate occurs selectively at the C=C bond according to Farmer s (anti-Markownikov) rule, giving the appropriate /3-adducts although propene and acetoxysilane are also formed as by-products ... 

More recently, Majetich et al. have proposed pentacoordinate allylsilicate intermediates formed from fluoride ion addition to silicon as an ambient nucleophilic species. However, nothing had been known so far about pentacoordinate allylsilicates, before we have initiated the present study, whereas a number of pentacoordinate organosilicates have been well characterized. It is an interesting problem whether the fluoride-catalyzed reactions actually involve free allyl anions or not. The author will discuss this problem in the next section somewhat in detail. In this section the author will describe preparation of well-defined pentacoordinate allylsilanes and their reactions which have been published recently. ... 

Oestreich and co-workers elaborated the 1,2-addition of silicon nucleophiles to aldehyde-derived imines (Scheme 19) [49]. As in the case of the related procedure for allylic substitution (Sect. 4.2), preformed chiral 6-membered NHC-copper(I)... 

So far, there is no conclusive evidence that a free allyl carbanion is generated from allylsilanes under fluoride ion catalysis. A hypervalent silyl anion, with the silicon still bonded to the allylic moiety, accounts equally well for the results obtained. Based on a variety of experimental results, it is in fact more likely that a nonbasic hypervalent silyl anion is involved rather than the basic free allyl carbanion first postulated14-23. When allylsilanes are treated with fluoride in the presence of enones. 1,4-addition takes place along with some 1,2-addition13. 

Although the allylation reaction is formally analogous to the addition of allylic boranes to carbonyl derivatives, it does not normally occur through a cyclic TS. This is because, in contrast to the boranes, the silicon in allylic silanes has little Lewis acid character and does not coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic TS. The -stereoisomer of 2-butenyl(trimethyl)silane gives nearly exclusively the product in... 

Acetylenic acrylates have been used to reduce side reactions in the preparation of acrylic sil(ox)anes by hydrosilylation [13,14], Allylic acrylates are known to result in addition products with both types of double bonds. Elimination of propene under loss of the allylic group is a major concern, because this path yields acryloxy silicone compounds with SiOC linkages of low hydrolytic stability. 

Cyclization reactions of vinyl- and alkynylsilanes have been reviewed100. The course of the reaction of the cyclohexenone derivative 184 depends on the catalyst employed ethylaluminium dichloride gives solely the product 185 of 1,6-addition, whereas tetrabuty-lammonium fluoride yields a mixture containing 69% of the 1,4-adduct 186 and 31% of the bridged compound 187 (equation 89)101. Intramolecular addition reactions of allylic silanes102 may also be catalysed by Lewis acids (equation 90) or fluoride ions, and in this case an allyl anion or a pentavalent silicon intermediate may be involved (equation 91). Such reactions are exemplified by the formation of a 1 5 mixture of the diastereomers 189 and 190 when the cyclohexenone derivative 188 is treated with ethylaluminium dichloride (equation 92). In the presence of fluoride anion the ratio of the isomers is reversed103. 

Quite recently, it was established that the formation of the pentacoordinated germanium and tin compounds EF4(CH2CH=CH2) from EF3(CH2CH=CH2) (E = Ge, Sn) by the addition of F is exothermic148. The nucleophilicity of the allylic y-carbon is much enhanced when the pentacoordinated EF4(CH2CH=CH2) is formed. These results are qualitatively similar to those found for the reaction of the corresponding silicon compound. The pentacoordinated Ge and Sn complexes have a significant Lewis acidity which allows them to form stable hexacoordinated intermediates in the course of the reaction. 

It is postulated that the mechanism of the silane-mediated reaction involves silane oxidative addition to nickel(O) followed by diene hydrometallation to afford the nickel -jr-allyl complex A-16. Insertion of the appendant aldehyde provides the nickel alkoxide B-12, which upon oxygen-silicon reductive elimination affords the silyl protected product 71c along with nickel(O). Silane oxidative addition to nickel(O) closes the catalytic cycle. In contrast, the Bu 2Al(acac)-mediated reaction is believed to involve a pathway initiated by oxidative coupling of the diene and... 

The class of 3-silyl-substituted reagents provides, upon addition with aldehydes, allylic silanes that offer many options for further derivatization. Oxidative processes are described in previous sections (see the sections on Preparation of 1,2-Diols and 1,4-Diols). If the appropriate silicon substituents are chosen, formal [3+2] cycloadditions with aldehydes can be promoted under Lewis acid catalysis. For example, the mismatched addition of the Z-3-propyl-3-benzhydryldimethyl allylsilane 183 to an a-benzyloxy aldehyde proceeds with low diastereofacial selectivity in favor of product 184 however, after protection of the secondary alcohol, an efficient [3+2] annulation provides the polysubsubstituted furan 185 in good yield and acceptable stereoselectivity (Scheme 24). ° The latter is brought forward to a tricyclic unit found in the antitumor natural product angelmicin B. 

Triethylsilyl acrylate can be induced lo undergo hydrolysis of the ethoxyl radicals to a desired extent forming linear or cross linked polymers. Addition polymerization will also lake place on the double bond of the acrylate radical. More stable monomers result from the use of allyl or vinyl groups instead of acrylates. The latter contain a silicon-oxygen-carhon linkage which is always more or less susceptible to hydrolysis. 

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