Reviews allylsilanes

Allylsilanes are widely used in organic synthesis1 4. They are stable with respect to 1,3-migra-tion of the silicon indeed high temperatures or catalysts are required for 1,3-equilibration5. The preparation of allylsilanes has been reviewed recently6-7. 

The Lewis acid-catalyzed reaction of 4-acetoxy-l,3-dioxanes with nucleophiles has been reviewed <2001TCC(216)51>. The principles of the reaction are displayed in (Equation 44). The combination of boron trifluoride and organozinc compounds was found to be very efficient <1997JOC6460, 1999JOC2026> but allylsilanes react as well <19%SL536, 1998TL6811>. 

Allyl- and vinylsilane chemistry was one of the first areas of reagent synthesis impacted by CM methodology. Allylsilanes are commonly employed in nucleophilic additions to carbonyl compounds, epoxides, and Michael acceptors (the Sakurai reaction) vinylsilanes are useful reagents for palladium-coupling reactions. As the ubiquitous application of CM to this substrate class has recently been described in several excellent reviews, this topic will not be discussed in detail, with the exception of the use of silane moieties to direct CM stereoselectivity (previously discussed in Section 11.06.3.2). 

Electrophilic substitution reactions of allylsilanes have been reviewed in detail by Fleming, Dunogues and Smithers118. 

The reactions of chiral allylsilanes with electrophiles to give diastereoselective products has recently been extensively reviewed by Masse and Panek166. An example is shown in equation 99. The reaction of the chiral allylsilanes 142 with phenylsulphenyl chloride (PSC) and chlorosulphonyl isocyanate (CSI) takes place with a diastereoselectivity which increases with the increasing steric bulk of the substituent R167. 

Allenylsilanes may behave as allyl or vinylsilanes. In general, allylsilane behaviour dominates over vinylsilane behaviour. The reactions of allenylsilanes with electrophiles have been comprehensively reviewed by Fleming, Dunogues and Smithers118. Electrophilic substitution of allenylsilanes gives alkynes (equation 106)173. 

There has been much interest in the chemistry of the trimethylsilyl group in the last few decades. This has led to many methodologies for the introduction of this group into organic compounds and a particularly good review on allylsilane chemistry has been published recently380. Probably the most important method of introducing a new carbon-silicon... 

In this sub chapter the most important synthetic aspect of the RCM of unsaturated organosilicon compounds will be discussed. For a general review on RCM see Refs. [59,122-124]. For a review on RCM of silyl dienes see Refs. [6,7]. A number of valuable synthetic applications have been proposed over the last few years. As follows from the data available, from the point of view of the application of RCM of vinyl and allylsilanes, the most important are silicon-tethered processes. For a general review on the silicon tethered processes see Refs. [125,126],... 

Catalytic asymmetric allylation of aldehydes and ketones with allylsilanes can be achieved by using chiral Lewis acids, transition metal complexes, and Lewis bases. In recent years, much attention has been paid for the chiral Lewis base-catalyzed system using allyltrichlorosilanes. Advances in catalytic asymmetric carbonyl allylation have been described in detail in recent reviews.116,117,117a... 

Other important feature of the allylsilane-TiC reagent system can be seen in 1,4-addition of an allyl group to a,/3-unsaturated ketones [248,249], illustrated in Eq. (94) [249]. This reaction has been reviewed [2,3,110,159-161,250] more examples can be seen in Table 9. 

Analogous to the allylation with allylsilanes and -stannanes, the transformations, vinylallylation, propargylation, allenylation, alkenylation, alkynylation, and arylation, are viable by the use of an appropriate reagent in the presence of a titanium Lewis acid these are surveyed in the review articles cited both in the Introduction and in this section. The stereochemistry of the reaction of a (vinylallyl)silane in the presence of TiCU has been reported [234]. Equation (113) shows that the major reaction of this silane and isobutyraldehyde occurred mainly in the anti sense with a ratio of anti to syn attack of 90 10 at the terminus remote from the silyl group. Essentially the same stereochemical outcome was observed for the same reaction with the corresponding trimethylsilyl derivative. The intramolecular reaction with an acetal, however, proceeded less selectively the anti syn ratio was 60 40 (Eq. 114) [234]. 

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. 

There is an extensive review of the electrophilic substitution reactions of allylsilanes and vinylsilanes in Organic Reactions and the reactions of allylstannanes have been reviewed briefly. The major books on synthetic organosilicon and organotin chemistry also cover the types of reaction discussed here. 

The reaction of propargyl alcohols with dicobalt octacarbonyl to give the complex salts 148 (X = BF4 or PF6) and synthetic uses of the latter have been reviewed. The salts react with electron-rich aromatic compounds ArH, such as anisole, phenol or N,N-dimethylaniline, to yield substitution products 149 after oxidative demetallation with an iron(III) or cerium(I V) salt with j5-diketones or j -keto esters the corresponding propargyl-substituted compounds 150 are obtained k Acetone reacts in an analogous fashion to give 151. The action of the cobalt complexes 148 on allylsilanes 152 leads to enynes 153. Indole reacts with the complex 148 (R = H R = R = Me) in the presence of boron trifluoride etherate to give 154, which was converted into 155 by the action of iron(III) nitrate " ... 

Although not driven by an external electrophile, two further methods of tetrahydrofuran synthesis are worthy of note in the context of this review. Firstly, Mohr has developed a neat approach to P-vinyltetrahydrofurans 223 in which an allylsilane function acts as the internal nucleophile in homoallylic alcohol 221 cyclizations, effectively by a 5-endo process involving an intermediate oxonium species 222 <93TL6251>... 

The 3-lactam 51 (Fig. 3), prepared either by CSI addition to 1,4-pentadiene [27a] or from a 4-acetoxyazetidin-2-one via displacement of the acetoxy group by an allylsilane, has also found application in the synthesis of carbapenems [27b]. Conversion of 51 to PS-5 has previously been reviewed [5c, f]. 

A soln. of allyltrimethylsilane in methylene chloride added dropwise to a pre-cooled soln. of dichlorobis(4-chlorophenoxy)methane and SnCl4 in the same solvent at — 78°, and worked up after 72 h - product. Y 78%. With subst. allylsilanes reaction proceeds mainly with double bond shift. F.e.s. H. Mayr et al.. Synthesis 1988, 962-3 review of electrophilic substitution of allylsilanes and vinylsilanes s. I. Fleming et al., Org. Reactions 37, 57-575 (1989). 

Annual surveys cover the Si-C bond for 1988 , with Organic Syntheses including Mc3SiCHN2, Me3SiCOMe, allylSnBu3, (Z)-4-Me3Si-3-buten-l-ol , and the use of Me3SiCH2MgCl to convert esters to allylsilanes. This review includes about 1660 references. 

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