Sakurai reaction

The Sakurai reaction (also known as the Hosomi-Sakurai reaction) is the chemical reaction of carbon electrophiles (such as a ketone shown here) with allylic silanes catalyzed by strong Lewis acids. [Hosomi, A.; Sakurai, H. "Tetrahedron Lett." 1976, 1295.] [Hosomi, A. "et al." "Chem. Letters" 1976, 941.] [Hosomi, A. "et al." "J. Am. Chem. Soc." 1977, 1977, "99", 1673.] [Hosomi, A. "Acc. Chem. Res." 1988, "21", 200-206. (Review)] [Fleming, I. "et al." "Org. React." 1989, "37", 57-575. (Review)] [Fleming, I. "Comp. Org. Syn." 1991, "2", 563-593. (Review)] It is named after the chemists Akira Hosomi and Hideki Sakurai. However this reaction should be renamed to be the Hosomi reaction. Because the chemist Akira Hosomi originally anticipates that the allylsilane indicates high nucleophilicity because of its low ionization potential during the investigation of photoelectron spectra of allysilanes and all of the reaction have been substantially carried out by Akira Hosomi.

Lewis acid activation is essential for complete reaction. Strong Lewis acids such as titanium tetrachloride, boron trifluoride, tin tetrachloride, and AlCl(Et)₂ are all effective in promoting the Hosomi reaction. The reaction is a type of electrophilic allyl shift with formation of an intermediate beta-silyl carbocation. Driving force is the stabilization of said carbocation by the beta-silicon effect.

The reaction has been applied in a Hosomi-Prins-Ritter multicomponent reaction with in step two a Prins reaction and in step three a Ritter reaction ["A Hosomi-Prins-Ritter Sequence for the Three-Component Diastereoselective Synthesis of 4-Amino Tetrahydropyrans" Oleg L. Epstein and Tomislav Rovis J. Am. Chem. Soc.; 2006; 128(51) pp 16480 - 16481; (Communication) DOI|10.1021/ja066794k] [In this sequence the dioxane 1 is activated by Lewis acid trimethylsilyl triflate as the reactive intermediate 2. This oxonium ion reacts in a Hosomi-Sakurai reaction with allyltrimethylsilane forming intermediate product 3 which is again activated this time by triflic acid to shortlived oxonium intermediate 4 and a Prins reaction follows to 5 whereby the transient carbocation is captured first by acetonitrile and then by water in a Ritter reaction. In this sketch R is a cyclohexyl group and t-Bu a tert-butyl group ] :

External links

* Hosomi-Sakurai reaction @ www.organic-chemistry.org [http://www.organic-chemistry.org/namedreactions/hosomi-sakurai-reaction.shtm Link]
* [http://www.geocities.jp/ksntsuku70/ Akira Hosomi HP]

References

ee also

* Grignard reaction