Allylsilanes with alkenes

The cross-coupling of allylsilanes with alkenes [50] and styrene [58] also occurs via their preliminary isomerization followed by the reaction of 1-propenylsilane with exemplary olefin-l-decene resulting in l-(triethoxysilyl)-1-decene as a product (Eq. 31). If the cross-coupling takes place, an expected product of this reaction is l-silyl-2-undecene, which is not detected. 

Scheme 3-64. Cross-metathesis of allylsilanes with alkenes.

The use of ill-defined catalysts for the cross-metathesis of allyl- and vinylsi-lanes has also received considerable attention, particularly within the past decade. Using certain ruthenium catalysts, allylsilanes were found to isomerise to the corresponding propenylsilanes prior to metathesis [5]. Using rhenium- or tungsten-based catalysts, however, successful cross-metathesis of allylsilanes with a variety of simple alkenes was achieved [6,7] (an example typical of the results reported is shown in Eq. 3). 

The Mo-catalysed cross-metathesis of acrylonitrile (59) [17,18] and allylsilane (60) [19] with alkenes 61 and 62 produced cross-products 63 and 64 with high selectivity. Reaction of 1-octene with 2 equivalents of styrene (65) afforded 66 in 89% yield. Only small amounts of stilbene (68) and 67 as the homoproducts were formed [23]. 

The Lewis acid-catalyzed reactions of allylsilanes with simple alkenes and alkynes introduce both allyl and silyl groups into the unsaturated bonds (Equations (53) and (54)).209 210b These allylsilylations are 7-regiospecific with respect to allylsilanes. The /raor-addition of allylsilanes occurs in the reaction with alkynes. There are two possible mechanisms for the Lewis acid-promoted allylsilylations, that is, trimethylsilyl cation- and Lewis acid-mediated pathways. 

N-Acyliminium ion pools react with various carbon nucleophiles as summarized in Scheme 5.16. For example, allylsilanes, silyl enol ethers, Grignard reagents, and 1,3-dicarbonyl compounds serve as good nucleophiles. Aromatic and heteroaromatic compounds also react as nucleophiles with N-acyliminium ion pools to give Friedel-Crafts-type alkylation products.N-Acyliminium ions are known to serve as electron-deficient 4n components and undergo [4 -F 2] cycloaddition with alkenes and alkynes. Usually these reactions take place very quickly, and therefore N-acyliminium ion pools serve as effective reagents for flash chemistry. 

The ene and Prins reactions are not mechanistically distinct. Coverage will therefore be organized by the nature of the carbonyl compound, with intermolecular reactions presented first, followed by intramolecular reactions. The emphasis will be on material published since the field has been reviewed " and on examples demonstrating the stereo-, regio- and chemo-selectivity of these reactions. Coverage is restricted to the addition of carbonyl and thiocarbonyl compounds to simple alkenes. Addition of carbonyl compounds to vinylsilanes, allylsilanes and enol ethers is covered in the following chapters. Addition of imines and iminium compounds to alkenes is presented in Part 4 of this volume. Ene reactions with alkenes and alkynes as enophiles are covered in Volume 5, Chapter 1.1. Use of aldehydes and acetals as initiators for polyene cyclizations is covered in Volume 3, Chapter 1.6. 

Mayr, H., Gorath, G. 1995. Kinetics of the reactions of carboxonium ions and aldehyde boron trihahde complexes with alkenes and allylsilanes. 7. Am. Chem. Soc. 117 7862-7868. 

Allenes react with arylmagnesium halides and trialkylsilyl chlorides in the presence of a Pd(0)-catalyst, giving substituted allylsilanes with good (Z)-steieoselectivity (Scheme 2-55, eq. (a)). Alkyl fluorides in these reactions lead to mixtures of regioisomers of trisubstituted alkenes (Scheme 2-55, eq. (b)). ... 

The titanium species derived from sequential treatment of a-alkoxy-substituted allylsilanes with s-Butyllithium then Ti(0-i-Pr)4 engages in a Peterson alkenation reaction with aldehydes to give, via electrophilic attack at the a-terminus of the allyl anion, 2-oxygenated 1,3-butadienes which can be hydrolyzed to the corresponding vinyl ketone (eq 19). ... 

The 5 -zincate could not react directly with alkenes [89]. However, in the presence of TM catalyst, the silylzincation could also take place at terminal alkenes. The first such example was reported in 2005 by our group (Table 11) [90]. Catalyzed by Cp2TiCl2, SiSiNOL-zincate and terminal alkenes could be regio- and chemoselectively transformed into allylsilanes. It seemed that in the metalation, the silyl group was specifically introduced at the 1-position and the elimination at the 3-position was favored to form E- or Z-alkenes. Many active groups could be compatible with these reactions. 

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

A one-pot reaction between a tryptophan ester, benzotriazole, and 2,5-dimethoxytetrahydrofuran in acetic acid gives the diastereomeric benzotriazolyl tetracycles, 349, in good yield. Substitution of the benzotriazole by reaction with silyl enol ethers and boron trifluoride etherate gives the corresponding ketones 350 and 351, and reaction with allylsilanes gives the corresponding alkenes 352 and 353. If the boron trifluoride etherate is added to the mixture before the silane, elimination of benzotriazole from 349 is also observed (Scheme 83) <1999T3489>. 

In a second report by Blechert on the cross-metathesis of polymer-bound alkenes, an immobilised allylsilane 19 was reacted with a variety of highly func-... 

A subsequent publication by Blechert and co-workers demonstrated that the molybdenum alkylidene 3 and the ruthenium benzylidene 17 were also active catalysts for ring-opening cross-metathesis reactions [50]. Norbornene and 7-oxanorbornene derivatives underwent selective ring-opening cross-metathesis with a variety of terminal acyclic alkenes including acrylonitrile, an allylsilane, an allyl stannane and allyl cyanide (for example Eq. 34). 

Only recently a selective crossed metathesis between terminal alkenes and terminal alkynes has been described using the same catalyst.6 Allyltrimethylsilane proved to be a suitable alkene component for this reaction. Therefore, the concept of immobilizing terminal olefins onto polymer-supported allylsilane was extended to the binding of terminal alkynes. A series of structurally diverse terminal alkynes was reacted with 1 in the presence of catalytic amounts of Ru.7 The resulting polymer-bound dienes 3 are subject to protodesilylation (1.5% TFA) via a conjugate mechanism resulting in the formation of products of type 6 (Table 13.3). Mixtures of E- and Z-isomers (E/Z = 8 1 -1 1) are formed. The identity of the dominating E-isomer was established by NOE analysis. 

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