Allylation of a carbonyl ketone (compound containing a ketone group and two different functional groups) has been shown. In the given reaction, the electrophilic compound (carbon with a ketone group) is treated with titanium tetrachloride, a strong Lewis acid and allyltrimethylsilane. According to the general principle, the Lewis acid first activates the electrophilic carbon in presence of allyltrimethylsilane which then undergoes nucleophilic attack from electrons on the allylic silane.[5] The silicon plays the key role in stabilizing the carbocation of carbon at the β-position. Hosomi-Sakurai reaction is also applicable for other functional groups such as enones, where conjugate addition is usually seen. In figure 2, the Hosomi- Sakurai reaction has been shown using a cinnamoyl ketone. This reaction follows the same mechanism as the previous reaction shown here.
As displayed in the scheme, the Hosomi–Sakurai reaction is proposed to give a secondary carbocation intermediate. Secondary carbocations are high in energy, however it is stabilized by the silicon substituent ("β-silicon effect", a form of silicon-hyperconjugation).
Literature of historic interest
Sakurai, Hideki; Hosomi, Akira; Kumada, Makoto (1969). "Addition of trichloromethyl radicals to alkenylsilanes". The Journal of Organic Chemistry. 36 (4): 1764–1768. doi:10.1021/jo01258a052.
Hosomi, Akíra; Sakurai, Hideki (1976). "Syntheses of γ,δ-unsaturated alcohols from allylsilanes and carbonyl compounds in the presence of titanium tetrachloride". Tetrahedron Letters. 17 (16): 1295–1298. doi:10.1016/S0040-4039(00)78044-0. ISSN0040-4039.
Hosomi, Akira; Sakurai, Hideki (1 March 1977). "Chemistry of organosilicon compounds. 99. Conjugate addition of allylsilanes to .alpha.,.beta.-enones. A New method of stereoselective introduction of the angular allyl group in fused cyclic .alpha.,.beta.-enones". Journal of the American Chemical Society. 99 (5): 1673–1675. doi:10.1021/ja00447a080. ISSN0002-7863.
References
^Hosomi, Akira (1 May 1988). "Characteristics in the reactions of allylsilanes and their applications to versatile synthetic equivalents". Accounts of Chemical Research. 21 (5): 200–206. doi:10.1021/ar00149a004. ISSN0001-4842.
^Fleming, Ian; Dunoguès, Jacques; Smithers, Roger (2004), "The Electrophilic Substitution of Allylsilanes and Vinylsilanes", Organic Reactions, American Chemical Society, pp. 57–575, doi:10.1002/0471264180.or037.02, ISBN9780471264187
^Yamasaki, Shingo; Fujii, Kunihiko; Wada, Reiko; Kanai, Motomu; Shibasaki, Masakatsu (1 June 2002). "A General Catalytic Allylation Using Allyltrimethoxysilane". Journal of the American Chemical Society. 124 (23): 6536–6537. doi:10.1021/ja0262582. ISSN0002-7863. PMID12047165.