The Electrophilic Substitution of Allylsilanes and Vinylsilanes

Abstract

Allylsilanes and vinylsilanes usually react with electrophiles to give substitution. These reactions are conveniently understood as the reactions of alkenes that have been significantly but only slightly modified by the presence of the silyl group. In both reactions, substitution is favored over addition, and both the site of attack and the site of the double bond in the product are usually determined by the site of the silyl group in the starting material. In this chapter only the electrophilic substitution reactions of allylsilanes, vinylsilanes, and allenylsilanes is discussed. It is further restricted to the reactions of tetraorganosilanes because they are synthetically the most interesting in the laboratory. However, although they are not included in the tables, allylsilanes and vinylsilanes that react by addition rather than substitution or that are not tetraorganosilanes are referred to occasionally in the text wherever their reactions illuminate the discussion. Many of the features of the reactions discussed here are shared by the reactions of arylsilanes, ethynylsilanes, propargylsilanes, cyclopropylsilanes, and cyclopropylmethylsilanes. The methods by which allylsilanes and vinylsilanes are synthesized have been summarized in several places. Stereochemsitry of reactions of allenylsilanes and vinylsilanes is discussed. Scope and limitations include discussions of protodesilylation and deuterodesilyation and the use of carbon, nitrogen, and oxygen as electrophiles. Other electrophiles include phosphorus, sulfur, metals, halogens, and selenium. All of these are covered in the extensive tabular material

Stereocontrolled Total Synthesis of Natural Products with Characteristic Molecular Structures and Biological Activities

“…Our strategy for its synthesis is illustrated in Chart 8. We reasoned that the complete carbon framework of 60 would be constructed by an intramolecular Hosomi-Sakurai reaction 49,50) of the substrate 61 possessing allylsilane and p-benzoquinone moieties. Since the conjugate addition cyclization leading to the formation of oxaspirocycles had never been reported, the potential conversion intrigued us.…”

Application of the tandem thionium/N-acyliminium ion cascade toward heterocyclic synthesis

“…Since the previous examples of our tandem Pummerer/iminium ion cyclization involve aromatic pbonds, we decided to study several systems which possess a simple olefinic tether. The well documented reactivity of allylsilanes towards electrophiles 31 suggested that the acid promoted reaction of sulfinylenamide 61 should provide access to a bicyclic lactam. Indeed, treatment of 61 with pTsOH afforded the cyclized product 62 in 61% yield (Scheme 13).…”

Allyldimethylsilyl triflate: a self-catalyzed silyl nucleophile

“…Changes in the reaction procedure (particularly solvent and temperature changes) could minimize but not completely suppress this. Any traces of water were manifested by the formation of isopropoxysilanes 6, which, after subsequent complete hydrolysis of the reaction mixture, gave 2-propanol and 7 …”

“…The normal mechanism for electrophilic attack at allylsilanes5 is anti-SE2' (7) in which case the silyl group does not directly interact with the electrophile.Lewis acid complex 8 (Fig. 1).…”

“…However, a more appealing combination is that of silyl en01 ethers, carbonyl compounds, and TMSOTf, in which case the Lewis acid is truly catalytic (6). The carbon analogue of a silyl en01 ether, an allylsilane, reacts much less efficiently with carbonyl compounds (acetals generally yield better results) and only in unusual cases may TMSOTf be successfully used catalytically (7).…”